2026 Self-Employment Tax Rate Explained: A Complete Guide for Freelancers & Independent Contractors

Updated for 2026: This guide uses current IRS source boundaries for self-employment tax and estimated-tax planning. It is educational; a current Schedule SE, Form 1040-ES worksheet, wages, other income, state facts, and qualified review can change a taxpayer’s result.

Introduction

If you earn income from freelancing, consulting, gig work, or operating your own business, you may owe self-employment (SE) tax in addition to federal income tax. SE tax is how the Social Security and Medicare systems collect contributions from people in business for themselves. For 2026, the underlying mechanics remain consistent with prior years: SE tax is computed on your net earnings from self-employment, using Schedule SE, and paid throughout the year under the federal pay‑as‑you‑go system by withholding, estimated tax, or a blend of both.

This guide explains the 2026 self-employment tax rate, how the Social Security and Medicare portions interact, the 92.35% net‑earnings calculation rule, the annual Social Security wage‑base boundary, the Additional Medicare Tax thresholds, and the deduction for one‑half of your SE tax. It also ties SE tax directly to estimated‑tax planning and withholding decisions so you can align cash flow, penalty avoidance, and recordkeeping with current IRS instructions.

Important boundaries to keep in mind as you read:

• A person in business for themselves (for example, a sole proprietor, independent contractor, certain single‑member LLC owners, and partners) usually owes SE tax on net earnings of $400 or more.
• Net earnings for SE tax purposes are generally 92.35% of your net self‑employment income after ordinary and necessary business expenses.
• The statutory SE tax rate contains two parts: 12.4% for Social Security and 2.9% for Medicare.
• The Social Security portion applies only up to the annual Social Security wage base, which changes every year; the Medicare portion applies to all net earnings.
• An Additional Medicare Tax may apply at higher income levels based on filing status.
• You may deduct one‑half of SE tax when computing your adjusted gross income (AGI); the computation occurs on Schedule SE.
• Under the federal pay‑as‑you‑go system, withholding and estimated tax are the two payment paths you can use to cover SE tax and income tax during the year.

Throughout, we use qualified language—because results depend on your exact facts and current IRS instructions. Always verify with the 2026 Schedule SE and Publication 505 worksheets before you file or adjust payments.

Who owes self-employment tax and what income triggers it

Self-employment tax applies to individuals who are in business for themselves and have net earnings from self-employment of $400 or more for the year. Common categories include:

• Sole proprietors filing Schedule C
• Independent contractors who receive Forms 1099-NEC (and others paid without information returns)
• Qualifying single‑member LLC owners treated as disregarded entities for federal tax purposes
• Partners with self-employment income from a partnership
• Members of a qualifying joint venture who elect to be treated as sole proprietors for federal tax purposes

Key points to set your scope:

• It is your net earnings from self-employment—not gross receipts—that drive SE tax. You first subtract your ordinary and necessary business expenses to arrive at net profit or loss.
• The SE tax computation uses 92.35% of your net self‑employment income as the “net earnings” base. This factor is built into the Schedule SE calculation.
• If your year ends with a net loss from self-employment, you generally don’t owe SE tax for that business activity. However, keep separate records because a loss may still matter for your income tax calculation and for planning estimated‑tax payments across multiple income sources.
• Employees do not pay SE tax on wage income; wages are subject to FICA withholding by an employer. If you have both wage income and self-employment income, the SE tax applies to the self-employment portion and coordinates, through Schedule SE, with wage‑based Social Security limits. Confirm the coordination steps with current Schedule SE instructions.

The “$400 or more” net‑earnings threshold generally triggers the need to compute and report SE tax. This filing boundary is low on purpose—Congress designed Social Security and Medicare coverage to apply broadly to self‑employment activity. If you’re close to the threshold, keep especially careful records so you can confirm whether you crossed it.

The 2026 self-employment tax rate, the 92.35% rule, and how Schedule SE works

Two building blocks define the 2026 self-employment tax rate:

• Social Security portion: 12.4%, up to the annual Social Security wage‑base limit
• Medicare portion: 2.9%, with no wage‑base limit

Schedule SE (Form 1040) assembles your net earnings base and applies these rates. Three essentials guide most calculations:

1) Net earnings base uses 92.35% of net income

• You do not apply the SE tax rate to your business’s gross or even your unadjusted net profit figure from Schedule C. Instead, you multiply your net self‑employment income by 92.35%. This is the “net earnings from self‑employment.”
• This percentage reflects how the law treats the “employer-equivalent” portion of Social Security and Medicare within the self-employment system.

2) Social Security is capped at the annual wage base; Medicare is not

• Apply the 12.4% Social Security rate only to combined amounts up to the annual Social Security wage base, which changes each calendar year.
• The 2.9% Medicare rate applies to all net earnings from self‑employment.

3) Additional Medicare Tax may apply at higher income levels

• A separate Additional Medicare Tax may apply when your income exceeds a filing‑status‑based threshold. The thresholds are $250,000 for married filing jointly, $125,000 for married filing separately, and $200,000 for other filers.
• This additional tax is separate from the 2.9% Medicare portion and is computed considering your overall circumstances. For planning, consult current IRS guidance to determine whether and how it applies to your year.

Illustrative example (below the Social Security wage base):

• A freelance designer has $100,000 in net Schedule C income after expenses. For SE tax, multiply $100,000 by 92.35% to get $92,350 in net earnings. Assuming the Social Security wage base is not exceeded by wages or this self‑employment amount, the Social Security portion is 12.4% of $92,350, and the Medicare portion is 2.9% of $92,350. The sum is the SE tax before considering any Additional Medicare Tax. The designer would also compute the deduction for one‑half of SE tax as part of AGI.

This example is illustrative only. Your wage situation, wage‑base interaction, and any Additional Medicare Tax may change the outcome. Always run the exact Schedule SE worksheet in your software or by following the current IRS instructions.

A practical workflow for 2026: From records to Schedule SE to pay‑as‑you‑go

A reliable, repeatable workflow helps you avoid year‑end surprises and estimated‑tax penalties. Use this operational sequence during 2026:

1) Capture gross receipts and expenses as you go

• Track all business receipts (invoices, platform payouts, direct deposits, checks) and contemporaneously classify ordinary and necessary expenses. Keep support like receipts, mileage logs, and invoices.

2) Confirm net profit or loss each month or quarter

• Run a simple profit‑and‑loss report. This gives you a current net self‑employment figure after expenses and helps you decide whether you’re trending above the $400 annual net‑earnings threshold.

3) Estimate net earnings for SE tax

• Multiply your year‑to‑date net self‑employment income by 92.35% to approximate net earnings for SE tax. If your income is volatile, consider the annualized‑income approach described in Publication 505 when planning installments.

4) Check the Social Security wage‑base boundary

• Determine whether your self‑employment net earnings, combined as applicable with any Social Security‑covered wages, may exceed the annual wage base. You do not need the exact dollar limit to plan mid‑year; you just need to recognize whether you are likely below, near, or above it. Confirm the actual wage‑base figure as you prepare Schedule SE.

5) Consider Additional Medicare Tax thresholds

• Compare expected income to the Additional Medicare Tax thresholds: $250,000 (married filing jointly), $125,000 (married filing separately), and $200,000 (other filers). If you are near a threshold, Publication 505’s worksheets and annualized methods can help you time payments appropriately.

6) Compute a preliminary SE tax and the one‑half deduction

• Apply the 12.4% Social Security and 2.9% Medicare rates to the appropriate base, respecting the wage‑base boundary for Social Security. Derive the deduction for one‑half of SE tax, which reduces AGI. This deduction is part of federal income tax, not a reduction to business profit.

7) Decide your pay‑as‑you‑go mix

• Withholding and estimated tax are the two payment paths. If you have wages, you may be able to increase withholding enough to cover your SE tax and income tax on your business income. If you do not have wages, use estimated tax installments. Publication 505 provides current 2026 worksheets, required‑annual‑payment rules, and payment methods.

8) Make payments and document them

• When you pay, retain confirmations. If you adjust withholding through your employer, keep a record of the change and your rationale. If you pay estimated tax, retain the amounts, dates, and the calculation that supported each payment.

9) Update projections and rinse‑and‑repeat

• Revisit the process each month or quarter, especially if your income or deductions change materially, you add a new income stream, or you approach the wage‑base boundary or Additional Medicare thresholds.

Following this cycle improves accuracy on Schedule SE, helps you claim the deduction for one‑half of SE tax correctly, and aligns your pay‑as‑you‑go payments with current Publication 505 mechanics.

Social Security wage‑base boundary, Medicare portion, and the Additional Medicare Tax

Three separate layers govern Medicare and Social Security for self‑employed taxpayers:

1) Social Security wage‑base boundary

• The 12.4% Social Security component applies only up to the annual wage‑base limit, which changes each year. Earnings above the wage‑base amount are not subject to the Social Security part of SE tax.
• If you have wages with Social Security tax withheld and also have self‑employment income, the law prevents double‑collection above the wage base; Schedule SE coordinates the Social Security calculation with wage withholding. Confirm the coordination steps with current Schedule SE instructions when you file.

2) Standard Medicare portion

• The 2.9% Medicare component applies to all net earnings from self‑employment—there is no wage‑base limit on this portion.
• Because there is no cap, growth in your net earnings continues to increase the Medicare portion throughout the year.

3) Additional Medicare Tax

• At higher income levels, you may owe a separate Additional Medicare Tax. The thresholds are $250,000 for married filing jointly, $125,000 for married filing separately, and $200,000 for all other filing statuses.
• This additional tax is not part of the 2.9% standard Medicare portion. It is determined by your overall income and filing status under current IRS rules.
• Publication 505 covers pay‑as‑you‑go mechanics that can be used to plan for this additional liability, including adjusting wage withholding or making estimated payments timed to your income pattern.

Illustrative example (approaching the wage base and considering thresholds):

• A consultant expects a strong year, plus a spouse’s wages in a married filing jointly household. Early in the year, they project combined earnings that may cross the Social Security wage‑base boundary. For planning, they model SE tax assuming the Social Security portion stops at the boundary while the Medicare portion continues. They then review whether their joint income may also approach the $250,000 threshold for Additional Medicare Tax. To stay aligned with pay‑as‑you‑go rules, they use Publication 505 worksheets and consider increasing wage withholding rather than relying solely on estimates. This helps them manage mid‑year cash flow while avoiding surprises.

Because wage‑base amounts change annually and every household’s mix of wages and self‑employment is different, verify with current 2026 instructions before finalizing your return or adjusting payments.

The one‑half self‑employment tax deduction: Where it goes and why it matters

The tax law allows you to deduct one‑half of your self‑employment tax when computing adjusted gross income. This deduction:

• Is taken “above the line” in computing AGI, generally on Schedule 1 (Form 1040).
• Does not reduce your net self‑employment income or change the computation of SE tax itself. You first compute SE tax on Schedule SE, then you claim the deduction for one‑half of that computed tax in arriving at AGI.
• Can influence estimated‑tax planning. Publication 505 includes a 2026 estimated SE tax/deduction worksheet to help you integrate both the SE tax amount and the one‑half deduction into your year‑round calculations.

Practical implications for planning:

• If you only use gross receipts or unadjusted net profit to forecast income tax, you may overstate your AGI and therefore your projected income tax and estimated payments. Incorporating the deduction for one‑half of SE tax in your projections can produce a closer estimate under pay‑as‑you‑go rules.
• If you are adjusting withholding to cover SE tax, include the deduction’s impact on AGI in your internal model so the additional withholding targets are not overstated or understated.

Common pitfalls to avoid:

• Reducing Schedule C expenses by “half of SE tax” (that is not how the law works).
• Applying the deduction to net earnings before computing SE tax.
• Forgetting to include the deduction in your estimated‑tax worksheet, which can lead to conservative overpayments or, in other instances, understated installments.

Always complete the current Schedule SE computation or its equivalent in your software before you carry the one‑half deduction to your AGI worksheet.

Pay‑as‑you‑go mechanics: Estimated taxes, withholding, and annualization

Federal income tax is pay‑as‑you‑go. For 2026, you generally use one or both of the following to meet your obligations as the year unfolds:

• Withholding: Taxes withheld from wages and certain other payments
• Estimated tax: Your own direct quarterly payments to the IRS

Publication 505 explains how withholding and estimated tax work together to cover income tax, self‑employment tax, and certain other taxes. It also includes:

• The estimated‑tax worksheet and the 2026 estimated SE tax/deduction worksheet
• Required‑annual‑payment rules and high‑income rules
• Regular, equal‑installment methods and an annualized‑income method for uneven income
• Payment methods and instructions

Planning with withholding

• If you or your spouse have wage income, you may be able to adjust withholding amounts so that the total withholding covers both the tax on wages and the taxes on your self-employment income. This can be useful if you prefer to avoid separate estimated tax payments.
• Withholding is treated as paid ratably throughout the year under IRS rules, which may help with timing when your self‑employment income is uneven. Publication 505 explains how to evaluate this option.

Planning with estimated tax

• If you do not have wage withholding, or if withholding is insufficient or unavailable, you generally use estimated tax installments to meet your pay‑as‑you‑go obligations. Publication 505 provides the current rules for calculating required payments and for using the annualized‑income method when your income fluctuates.
• The annualized‑income method can be particularly helpful for freelancers whose revenue spikes in certain months. Using it may align your installments more closely with your actual cash flow and the timing of your income.

Blending methods

• Many self‑employed households use a blended approach—some increased wage withholding plus some estimated payments—to smooth cash flow and stay compliant.
• Keep documentation of how you derived each withholding change or estimate, especially if you use the annualized‑income method. Publication 505’s worksheets can serve as your calculation backbone.

Avoiding underpayment penalties

• The IRS can assess an underpayment penalty if you do not pay enough tax during the year through withholding and estimated tax. Publication 505 explains the required‑annual‑payment rules and methods to compute and, where eligible, avoid or reduce penalties.
• Rather than adopting a flat percentage of “every dollar earned,” base your installments on your actual facts using the current worksheets. This is especially important when Social Security wage‑base coordination or the Additional Medicare Tax may change the mid‑year math.

Common error patterns and decision paths that trip up filers

Even experienced freelancers encounter avoidable errors. Here are patterns to watch for and practical decision paths to stay on track:

Frequent errors

• Skipping the $400 net‑earnings threshold test and failing to compute SE tax on a profitable side gig
• Applying the 15.3% combined rate to gross receipts instead of net earnings after expenses
• Forgetting to multiply by 92.35% to arrive at “net earnings from self‑employment”
• Misapplying the Social Security wage‑base boundary or overlooking wage‑base coordination with W‑2 wages
• Ignoring the possibility of Additional Medicare Tax at higher income levels
• Omitting the deduction for one‑half of SE tax when computing AGI
• Using a single “rule of thumb” percentage for estimates instead of the Publication 505 worksheets, causing mismatches and potential penalties
• Paying estimates but not retaining payment confirmations, complicating reconciliation at filing

A straightforward decision path

• Do I expect net self‑employment income after expenses this year? If no or a net loss, you may not owe SE tax, but continue recordkeeping. If yes, proceed.
• Will annual net earnings from self‑employment be $400 or more? If yes, expect to complete Schedule SE and compute SE tax. If no, continue tracking in case later months change the outcome.
• Do I also have wage income? If yes, consider using withholding adjustments to cover some or all of your self‑employment and income tax. Confirm Social Security wage‑base coordination in the current Schedule SE instructions.
• Is my total income stable or uneven? If uneven, review Publication 505’s annualized‑income method for installment planning.
• Am I near the annual Social Security wage‑base amount or an Additional Medicare threshold? If yes, be cautious about mid‑year assumptions and verify with the current worksheets.
• Do I have documentation to support my Schedule C expenses and my SE tax computation? If not, tighten your recordkeeping now to prevent filing delays.

A single misstep—such as forgetting the 92.35% factor or not integrating the one‑half SE tax deduction into your AGI—can snowball into inaccurate estimates and unexpected balances due. Use the current IRS worksheets and capture each assumption you make so you can revisit it if your income changes.

Choosing your payment path: A one‑page decision table

The right payment setup depends on your income mix, volatility, and comfort with setting aside cash. Use this quick reference to decide how to cover self‑employment tax and income tax during 2026.

Situation	Recommended path to consider	Why it may help	What to confirm before acting
You have a W‑2 job plus a growing side business	Increase wage withholding to cover both wage and self‑employment taxes; revisit each quarter	Withholding counts as paid evenly during the year, which can smooth uneven side‑gig income	Publication 505 withholding guidance; current Schedule SE interaction with Social Security wage‑base limits
You rely entirely on 1099 income with steady monthly receipts	Use the regular equal‑installment method for estimated tax	Predictable receipts fit equal installments; easy to automate	Publication 505 estimated‑tax worksheet (including SE tax and the one‑half SE tax deduction)
Your income is highly seasonal or lumpy	Use the annualized‑income method described in Publication 505	Aligns installments with when you actually earn income; can reduce underpayment risk in off‑months	Proper period‑by‑period records and the current annualization worksheet
You expect to approach the Social Security wage base	Run projections that stop the Social Security portion at the boundary; continue Medicare without a cap	Prevents overestimating the Social Security share of SE tax	The actual 2026 wage‑base amount and the current Schedule SE instructions
You may cross an Additional Medicare Tax threshold	Plan for the possible additional tax; consider increasing withholding or adjusting installments	Addresses an extra layer of tax tied to filing status and total income	Thresholds: $250,000 MFJ, $125,000 MFS, $200,000 others; Publication 505 mechanics
You prefer fewer transactions	Rely more on withholding, if available, and schedule fewer, larger estimated payments if needed	Reduces administrative burden while staying pay‑as‑you‑go compliant	Employer capability to adjust withholding; Publication 505 timing rules

This table is a starting point. Your mix of deductions, credits, and outside income can change outcomes. Verify with the current worksheets before moving cash.

Recordkeeping that supports Schedule SE, estimated tax, and year‑end accuracy

Robust records make Schedule SE straightforward and keep your estimated‑tax calculations defensible. In practice, that means documenting both your business activity and your pay‑as‑you‑go payments.

Capture income systematically

• Retain copies of all invoices, client contracts, payout statements from platforms, bank deposit records, and any Forms 1099‑NEC you receive.
• Track non‑1099 income as carefully as 1099 income; SE tax applies to your net self‑employment income, whether or not a form is issued.

Document expenses contemporaneously

• Maintain receipts, bills, and proof of payment for ordinary and necessary business expenses. Keep logs for items that require ongoing substantiation, such as mileage.
• Categorize expenses consistently to speed up the Schedule C process, because accurate Schedule C figures flow directly into Schedule SE via your net profit.

Preserve SE tax computations

• Keep copies of your interim SE tax projections showing net earnings (92.35% of net income), Social Security/Medicare splits, and any assumptions about the wage‑base boundary.
• Retain the computation behind the deduction for one‑half of SE tax so you can reconcile to AGI projections and Publication 505 worksheets.

Track pay‑as‑you‑go activity

• For wage withholding changes, save the date, the change request, and subsequent paystubs to verify that withholding updated as intended.
• For estimated tax, save confirmations for each payment, the amount, the date, and the specific quarter or period to which it applies. If you use the annualized‑income method, preserve the period calculations.

Coordinate across multiple income sources

• If your household has both wages and self‑employment income, keep a consolidated summary. This makes it easier to check Social Security wage‑base interactions and to assess whether Additional Medicare Tax may apply.
• Maintain a running AGI estimate that includes the deduction for one‑half of SE tax. This helps align your pay‑as‑you‑go decisions with your evolving income picture.

Good records reduce the time it takes to complete the 2026 Schedule SE, support the accuracy of your AGI and deductions, and make it simpler to choose between withholding and estimated payments as your income changes.

Frequently Asked Questions

What is the 2026 self-employment tax rate and how do the Social Security and Medicare portions work?

The 2026 self-employment tax rate is composed of two parts: 12.4% for Social Security and 2.9% for Medicare. You apply these rates to your “net earnings from self-employment,” which are generally 92.35% of your net self-employment income after ordinary and necessary business expenses. The Social Security portion applies only up to the annual Social Security wage-base limit, which changes every year. The Medicare portion applies to all of your net earnings from self-employment. If your overall income is high, a separate Additional Medicare Tax may also apply based on filing status. You compute the SE tax on Schedule SE and then claim a deduction for one-half of the SE tax in arriving at adjusted gross income.

Who has to file Schedule SE and what is the $400 net earnings threshold for self-employment tax?

If you are in business for yourself—as a sole proprietor, independent contractor, qualifying single-member LLC owner, or partner—you generally must compute self-employment tax when your net earnings from self-employment are $400 or more for the year. Net earnings are not your gross receipts; they’re typically 92.35% of your net self-employment income after ordinary and necessary business expenses. When you meet or exceed the $400 threshold, you complete Schedule SE to calculate the Social Security and Medicare components of SE tax. If you also have W-2 wages, your wage withholding covers the employee FICA portion on those wages, and Schedule SE addresses the self-employment portion. Always confirm your filing need against current Schedule SE instructions for the year.

Why does Schedule SE use 92.35% of my net self-employment income, and which expenses reduce that base?

The 92.35% factor reflects how the law treats the “employer-equivalent” side of Social Security and Medicare in the self-employment system. Instead of applying rates to your gross receipts, you first subtract ordinary and necessary business expenses to arrive at net profit or loss (for example, on Schedule C). Then you multiply that net by 92.35% to determine “net earnings from self-employment,” which is the base for applying the 12.4% Social Security and 2.9% Medicare portions. Typical business expenses—those that are ordinary and necessary for your trade—reduce the base before the 92.35% factor applies. The exact categories and any limitations depend on your facts; use current IRS instructions when classifying expenses.

How does the Social Security wage base affect my self-employment tax if I also have wages from a job?

The Social Security portion of self-employment tax (12.4%) applies only up to the annual Social Security wage base, which changes each year. If you have W-2 wages with Social Security tax withheld, Schedule SE generally coordinates your self-employment Social Security calculation so you do not pay the Social Security portion above the annual limit. Your Medicare portion (2.9%) still applies to all net earnings from self-employment, regardless of wages. Because coordination depends on your total wages and your net earnings from self-employment for the year, verify the treatment with the current Schedule SE instructions and make sure your records reflect year-to-date wages and withholding when you prepare your return.

What is the Additional Medicare Tax and when might it apply to self-employment income?

The Additional Medicare Tax is a separate tax that can apply at higher income levels based on filing status. The thresholds are $250,000 for married filing jointly, $125,000 for married filing separately, and $200,000 for all other filers. It is distinct from the standard 2.9% Medicare portion of self-employment tax. Whether it applies depends on your overall income picture, including wages and self-employment income. If you expect to be near a threshold, Publication 505’s pay‑as‑you‑go rules and worksheets can help you project any Additional Medicare Tax and decide whether to increase wage withholding or adjust estimated tax payments during the year. Confirm applicability with current IRS guidance before you file.

Where do I deduct one-half of my self-employment tax and does it change how much I pay during the year?

After you compute your self-employment tax on Schedule SE, you may deduct one-half of that amount in arriving at adjusted gross income, typically on Schedule 1 (Form 1040). This is an “above-the-line” deduction. It does not reduce your net self-employment income or change the way SE tax itself is calculated. However, the deduction can affect your income tax computation and therefore your pay‑as‑you‑go strategy. Publication 505 includes a 2026 estimated SE tax/deduction worksheet so you can reflect both the SE tax and the related deduction when projecting quarterly installments or deciding how much withholding to add at work. Always base your adjustments on the current worksheets.

If I have a W-2 job and a side gig, do I still need to make quarterly estimated tax payments?

Maybe. Federal tax is pay-as-you-go, and there are two ways to pay during the year: withholding and estimated tax. If your W-2 withholding is high enough to cover the income tax and self-employment tax attributable to your side gig (as well as tax on your wages), you may not need separate estimated payments. Many people in this situation increase wage withholding to stay compliant. If withholding falls short, estimated tax installments can make up the difference. Publication 505 explains required-annual-payment rules, the regular and annualized methods for computing installments, and payment options. Revisit your numbers during the year, especially if income becomes more volatile than expected.

How should I keep records for Schedule SE and to support my 2026 estimated tax calculations?

Good records start with accurate income tracking—retain invoices, payout statements, and bank records, including any Forms 1099-NEC. For expenses, keep receipts, bills, and contemporaneous logs (such as mileage). Organize expenses by category so that your Schedule C net profit flows cleanly into Schedule SE. Preserve your interim self-employment tax projections, including the 92.35% net-earnings calculation, Social Security and Medicare portions, and any assumption about the Social Security wage-base boundary. If you adjust wage withholding, keep documentation of the change and paystubs showing the updated amounts. For estimated tax, save confirmations with dates and amounts. Strong records make it easier to use Publication 505’s worksheets accurately and to reconcile payments at filing.

Sources

• IRS Topic No. 554 — Self-Employment Tax: https://www.irs.gov/taxtopics/tc554
• IRS Publication 505 — Tax Withholding and Estimated Tax: https://www.irs.gov/publications/p505