Quick answer: if you have a W-2 job, you can cover the tax on your side hustle profit by having more federal income tax withheld from your paycheck instead of (or in addition to) making quarterly estimated payments. Submit a new Form W-4 to your employer and either list expected side income in Step 4(a) or enter a flat extra amount per pay period in Step 4(c). The IRS Tax Withholding Estimator can calculate the amount. Withholding counts toward both income tax and self-employment tax, and the IRS generally treats it as paid evenly through the year, which can help you avoid underpayment penalties.
Side hustle income does not come with automatic tax withholding. That is why the IRS expects many self-employed people to make quarterly estimated payments. But if you also have a W-2 job, there is often a simpler option: let your paycheck do the work.
This guide explains how to use Form W-4 to cover side hustle taxes, how to calculate the extra amount, and when this approach works better or worse than estimated payments. For choosing and starting a hustle, see our guide to side hustle ideas.
Sources: Internal Revenue Service, Form W-4 (2026) and instructions, Tax Withholding Estimator page, Publication 505 (Tax Withholding and Estimated Tax), Form 2210 instructions (underpayment of estimated tax), Self-Employment Tax page, Estimated Taxes page. General information, not tax advice. Checked October 2026.
Why Side Hustlers Owe Tax During the Year
The U.S. tax system is pay-as-you-go. IRS Publication 505 explains that you must pay tax as you earn income, either through withholding or estimated tax payments. Employers withhold from wages, but no one withholds from freelance, gig or small business income.
Side hustle profit is subject to two taxes:
- Income tax at your regular rate.
- Self-employment tax of 15.3% on 92.35% of net earnings, covering Social Security and Medicare, once net earnings reach $400.
If too little is paid during the year, you may owe an underpayment penalty on top of the tax itself. The general rule is that you may need to make estimated payments if you expect to owe $1,000 or more when you file, after subtracting withholding and refundable credits.
How Withholding Can Replace Estimated Payments
Federal income tax withheld from your wages is applied to your total tax bill, not just the tax on wages. That total includes self-employment tax. So extra withholding from your day job can cover what you owe on hustle profit.
There is a timing advantage, too. According to the Form 2210 instructions, withholding is generally treated as paid evenly throughout the year, regardless of when it actually came out of your paycheck. Estimated payments, in contrast, count on the date you make them. That means increasing withholding in October can still help cover an underpayment from earlier in the year, while a late estimated payment cannot fix earlier quarters.
Two Ways to Use Form W-4
The current Form W-4 offers two lines that work for side income.
Step 4(a): Other income
Step 4(a) is for other income not from jobs, such as interest, dividends or retirement income. The instructions say you can include other income here if you want tax withheld on it rather than making estimated payments. Your employer’s payroll system then calculates extra income tax withholding as if that income were part of your pay.
The limitation is that Step 4(a) only reflects income tax. It does not account for self-employment tax, so side hustlers usually need to add more on top.
Step 4(c): Extra withholding
Step 4(c) lets you enter a flat additional amount to withhold each pay period. This is usually the simplest choice for side hustlers, because you can calculate one number that covers both income tax and self-employment tax and spread it across your remaining paychecks.
How to Calculate the Extra Amount
The most accurate option is the IRS Tax Withholding Estimator. The IRS says it takes about 25 minutes and asks about your household, income and deductions. You will need recent pay stubs and payment records for self-employment or gig work. The estimator can produce a pre-filled W-4 that you give to your employer. It does not ask for your name or Social Security number and does not save your answers.
To estimate by hand, follow these steps:
- Estimate your side hustle net profit for the year (income minus business expenses).
- Estimate self-employment tax: profit x 0.9235 x 0.153.
- Estimate income tax on the profit: subtract half of the SE tax, and any QBI deduction you expect, then multiply by your marginal tax bracket.
- Add the two figures for your total extra tax.
- Subtract anything you have already paid through estimated payments.
- Divide by the number of paychecks left in the year.
A Worked Example
Here is a hypothetical case. Suppose you expect $10,000 in side hustle profit for the year and are in the 22% federal bracket. You have 10 paychecks left.
| Step | Calculation | Result |
|---|---|---|
| Self-employment tax | $10,000 x 0.9235 x 0.153 | About $1,413 |
| Half of SE tax deduction | $1,413 / 2 | About $706 |
| Income tax on profit | ($10,000 – $706) x 22% | About $2,045 |
| Total extra tax | $1,413 + $2,045 | About $3,458 |
| Extra withholding per paycheck | $3,458 / 10 | About $346 |
This simplified example ignores the QBI deduction, state taxes and other factors, which could lower the federal figure. It is meant to show the method. Your own numbers will differ, which is why the IRS estimator is the better tool.
When Withholding Works Best
Using your W-4 tends to make the most sense when:
- Your side hustle profit is fairly steady and predictable.
- You have a regular W-2 paycheck large enough to absorb the extra withholding.
- You prefer not to track four estimated payment deadlines.
- You fell behind earlier in the year and want to catch up without a penalty for earlier quarters.
When Estimated Payments Are Better
Quarterly estimated payments may suit you better when:
- Hustle income is irregular, with big months and slow months.
- You want to pay based on actual results rather than an annual guess.
- Your day job paycheck is too small to cover the extra amount.
- You plan to leave your job during the year.
- You want to keep more of your paycheck flexible and set money aside yourself.
Many side hustlers use a mix: a modest Step 4(c) amount as a baseline plus an estimated payment after a strong quarter.
How the Safe Harbor Rules Apply
Whether you use withholding, estimated payments or both, the IRS safe harbor rules determine whether you owe an underpayment penalty. You generally avoid the penalty if your withholding and timely estimated payments total at least the smaller of 90% of this year’s tax or 100% of last year’s tax. That second figure rises to 110% if last year’s adjusted gross income was over $150,000 ($75,000 if married filing separately).
The prior-year option is useful for side hustlers whose income is growing. If your withholding alone covers 100% (or 110%) of last year’s total tax, you are generally protected from the penalty even if you owe more at filing time. You would still need to pay the balance by the April deadline.
Step-by-Step: Submitting a New W-4
- Download the current Form W-4 from IRS.gov, or use your employer’s payroll portal, which often has an online version.
- Complete Step 1 with your filing status. Complete Steps 2 and 3 only if they apply, such as multiple jobs in the household or dependents.
- Enter your extra per-paycheck amount in Step 4(c), or other income in Step 4(a) if you prefer that method.
- Sign and date the form, then submit it to your employer or payroll department.
- Check your next pay stub to confirm the higher federal withholding took effect.
- Track the extra withholding on each stub through the year, so you know how much has been paid toward the hustle’s tax.
Employers generally put a new W-4 into effect within a pay period or two, so give yourself time before year-end if you are catching up.
Other Sources of Withholding
Withholding does not have to come from a job. Retirees with side income can increase withholding from a pension or annuity with Form W-4P. People receiving Social Security benefits or unemployment compensation can request voluntary federal withholding on those payments with Form W-4V, according to the IRS. Any of these can help cover side hustle tax, because all federal withholding counts toward your total bill.
Updating Your W-4 Through the Year
You can submit a new W-4 to your employer at any time. The IRS recommends checking withholding every January and after major changes, such as new paid work or a major income change. If you raise withholding during the year, you may need to update it again in late December so next year’s withholding is right.
Keep notes of what you changed and why. A simple log with the date, the Step 4(c) amount and the profit estimate behind it makes the next adjustment much faster, and it helps if you ever need to explain the change to a tax professional. When you file, compare total withholding on your W-2 with your actual tax to fine-tune next year’s amount.
Married Couples and Two Jobs
If you file jointly, extra withholding can come from either spouse’s paycheck, because the tax is figured on the joint return. Couples sometimes add the Step 4(c) amount to whichever paycheck is larger or more stable. The IRS estimator handles two-earner households when you enter both sets of pay stubs.
What Withholding Does Not Cover
- State taxes. Federal W-4 changes do not affect state income tax withholding. Many states have their own withholding forms.
- Business recordkeeping. You still need to track income and expenses and file Schedule C and Schedule SE.
- Other income-related obligations, such as sales tax collected from customers.
Our guides to tracking side hustle income and expenses and side hustle taxes for beginners cover the filing side. Moving a set percentage of every payment into a separate bank account is still a good habit, even if withholding covers the tax.
Common Mistakes
A few errors come up again and again with this approach. Watch for these:
- Using only Step 4(a) and forgetting that it does not include self-employment tax.
- Guessing once and never checking as hustle income changes.
- Forgetting state tax when you only update the federal W-4.
- Leaving the extra withholding in place after the hustle ends, which ties up money until your refund arrives.
- Assuming no 1099 means no tax. All side hustle income is taxable whether or not you get a form.
Frequently Asked Questions
Frequently Asked Questions
Can I pay side hustle taxes through my W-2 job? Yes. You can increase federal income tax withholding with a new Form W-4. Withholding is applied to your total federal tax, including self-employment tax.
Should I use Step 4(a) or Step 4(c) for side hustle income? Step 4(c) is usually simpler because you can enter one amount covering both income tax and self-employment tax. Step 4(a) only adjusts income tax withholding.
Does extra withholding count as paid evenly during the year? Generally yes. Under the Form 2210 rules, withholding is treated as paid evenly throughout the year unless you choose otherwise, which can reduce or remove underpayment penalties.
Do I still need to make quarterly estimated payments? Not if your withholding is enough to meet the safe harbor rules. Many people combine withholding with an occasional estimated payment.
How do I figure out how much extra to withhold? Use the IRS Tax Withholding Estimator, or estimate your side hustle profit, calculate self-employment tax and income tax on it, and divide by your remaining paychecks.
Will my employer know about my side hustle? Your employer only sees the W-4 amounts. A Step 4(c) figure does not explain what it is for.
The Bottom Line
For side hustlers with a steady paycheck, Form W-4 withholding can be an easier way to stay current on taxes than four estimated payments a year. Use the IRS estimator or the step-by-step math above, enter the extra amount in Step 4(c), and revisit it whenever your side income changes. Withholding counts toward self-employment tax too, and its even-timing treatment can help you catch up late in the year.