Enter your annual income, filing status, what's already been withheld, your deductions, and credits — and get an estimate of your federal refund or tax owed before you file.
The worst time to find out you owe $3,400 in federal taxes is when you open your tax software in February. The best time is now, with enough months left in the year to adjust your W-4 withholding or make a Q4 estimated tax payment. This estimator takes your Annual Gross Income, Filing Status, Federal Tax Already Withheld, deductions choice, tax credits, and any additional income to run the calculation before it matters.
The results show your estimated federal tax liability, what has already been withheld, and whether the difference is a refund coming to you or an amount you will owe. The What This Means section explains the gap in plain terms. The Simulated Income panel lets you test a different income scenario — useful if you had a freelance project, a job change, or investment income that changed your tax situation mid-year.
How withholding works — and why mismatches happen
Your employer withholds federal income tax from each paycheck based on the W-4 you filed when you were hired, using IRS withholding tables that estimate your annual tax. When your actual tax situation differs from what the W-4 assumed — more income from a side gig, a change in filing status after marriage or divorce, investment distributions, or a second job — withholding falls short of what you actually owe.
The reverse also happens: too much withholding throughout the year means a large refund, which feels good but is economically equivalent to giving the government an interest-free loan. The estimator helps you find the right level — close enough that you do not owe a penalty, but not so over-withheld that your take-home pay is being suppressed unnecessarily.
Standard versus itemized deductions: which reduces your liability more
The Standard or Itemized Deductions field lets you choose the basis for your deductions. The 2026 standard deduction is $15,000 for single filers and $30,000 for married filing jointly. Most filers take the standard deduction because itemized deductions — mortgage interest, state and local taxes up to $10,000, charitable contributions, and major medical expenses — do not exceed that threshold.
If your mortgage interest, state taxes, and charitable giving sum to $32,000 and you are married filing jointly, itemizing adds $2,000 to your deduction. On a 22% marginal rate, that saves $440 in federal tax. Worth claiming, but not dramatic. Use the Itemized Amount field if you choose itemized and enter your realistic total. The estimator applies whichever deduction basis you select.
Tax credits: the deductions that actually reduce the check you write
Tax credits reduce your tax liability dollar for dollar — a $2,000 child tax credit cuts your tax bill by $2,000, not your taxable income by $2,000 at your marginal rate. The Tax Credits field captures credits including the Child Tax Credit ($2,000 per qualifying child in 2026), Child and Dependent Care Credit, education credits, and earned income credit. These are worth entering accurately because they directly change the refund-versus-owe calculation.
Do not confuse credits with deductions. A deduction reduces taxable income; if you are in the 22% bracket, a $1,000 deduction saves $220. A $1,000 credit saves $1,000. Credits are the more powerful tax variable, particularly for families with dependent children. Enter the total credit amount you expect to claim, not the number of children or the care expenses themselves.
Additional income: freelance, investments, and other non-W-2 sources
The Additional Income field captures earnings for which no federal tax has been withheld — freelance or self-employment income, consulting fees, rental income, capital gain distributions, and other 1099 sources. These are fully taxable at your marginal rate (plus 15.3% self-employment tax for freelance income above $400), and the gap between what you owe on them and what has been withheld is the most common source of unexpected tax bills.
If you earned $18,000 in freelance income this year on top of a $65,000 salary, your marginal federal tax on the freelance portion is 22%, plus self-employment tax — adding roughly $4,000–$7,000 to your liability depending on deductions. None of that was withheld from your W-2 paycheck. Enter it in Additional Income and the estimator will show you what it costs so you can plan accordingly before filing.
Using the simulation panel to test a changed income scenario
The Simulated Income panel lets you run a second scenario without losing your original inputs. If you are considering a Roth conversion, a large bonus, or a freelance contract that would close this calendar year, enter the incremental income and see how it shifts your refund or liability. This is particularly useful for decisions that are time-sensitive before December 31.
A $20,000 Roth conversion on top of $75,000 in W-2 income pushes the top $15,000 of that conversion into a higher bracket. The simulation shows you the tax cost in real dollars so you can weigh it against the long-term Roth benefit. Year-end income planning is most valuable when you know the tax cost before you commit — run the simulation now, while you still have time to act before December 31.
How to use it
- Enter Annual Gross Income (your W-2 box 1 equivalent, or projected annual if mid-year) and select your Filing Status.
- Enter Federal Tax Already Withheld — find this on your most recent pay stub in the YTD federal income tax box, or multiply your latest period withholding by the number of pay periods in the year.
- Choose Standard or Itemized Deductions and enter the Itemized Amount if itemizing.
- Enter your expected Tax Credits and any Additional Income with no withholding.
- Read the estimated federal tax liability, refund, or amount owed in the results, then use the Simulated Income section to test a different income scenario.
Who it's for
- W-2 employee who started a side business mid-year — Earns $72,000 from a salary job with $8,900 withheld. Adds $22,000 in freelance consulting income in Additional Income. Estimator shows $6,100 owed at filing — enough to prompt a Q4 estimated tax payment to avoid an underpayment penalty.
- Married couple who had a second child during the year — Combined W-2 income of $114,000 with two Child Tax Credits ($4,000 total). The credits offset most of their liability; the estimator shows a $1,250 refund — confirming their current withholding is reasonably calibrated after the family change.
- Retiree managing distributions and Social Security — Has $28,000 in Social Security (85% taxable = $23,800) and $32,000 in IRA distributions. Enters both as income with minimal withholding. Estimator shows $4,200 owed — prompting either IRA withholding adjustments or quarterly estimated payments.
- Individual planning a year-end Roth conversion — Has $88,000 in W-2 income. Uses the Simulated Income panel to test adding $15,000 in Roth conversion income. The simulation shows marginal tax cost of $3,300 on the conversion — useful data for deciding whether to convert now or wait.
Key terms
- Federal tax withholding
- The amount of federal income tax an employer deducts from an employee's paycheck throughout the year and remits to the IRS. The W-4 form determines the withholding amount based on income, filing status, and claimed adjustments.
- Standard deduction
- A fixed reduction to taxable income available to all filers without itemizing. In 2026, $15,000 for single filers and $30,000 for married filing jointly. Over 90% of filers take the standard deduction.
- Tax credit
- A dollar-for-dollar reduction in tax liability. A $2,000 tax credit reduces what you owe by $2,000, regardless of your marginal tax rate. More valuable than deductions of equivalent dollar value.
- Marginal tax rate
- The tax rate applied to the last dollar of income in a given bracket. Withholding accuracy depends on knowing your marginal rate because additional income (freelance, bonuses, conversions) is taxed at the marginal rate, not an average rate.
Frequently asked questions
Where do I find my federal tax already withheld mid-year?
Check your most recent pay stub — look for Federal Income Tax in the year-to-date (YTD) column. That number is the total withheld so far this year. If you want a full-year estimate, take your per-period withholding and multiply by total pay periods in the year (26 for biweekly, 24 for semi-monthly, 12 for monthly).
Does this include state income taxes?
No — this estimator calculates federal income tax only. State tax rates and rules vary significantly by state. Your state's department of revenue may offer a similar estimator for state liability. The federal and state calculations are independent; run each separately for a full picture.
What if my income varied a lot during the year?
Use your best estimate of full-year income across all sources. If you had a high-income first half and expect a slow second half, estimate the full-year total based on what you know. The estimator works on annual figures, so the most accurate result comes from the most accurate full-year income estimate you can make at the time.
How do I handle self-employment tax in the calculation?
Self-employment tax (15.3% on the first $168,600 of net self-employment income in 2026, 2.9% above that) is separate from income tax. The calculator estimates federal income tax; SE tax is an additional liability for freelancers and self-employed individuals that adds to the amount owed beyond income tax. Add roughly 14% of net self-employment income (after the SE deduction) to your estimated liability for a full picture.