Your tax return calculation comes down to a simple comparison: how much tax you owe for the year versus how much you already paid through withholding or estimated payments. If you paid more than you owe, you get a refund. If you paid less, you owe the difference. The real work is figuring out that “how much you owe” number, and it follows a straightforward sequence of steps.
Start With Your Total Income
Gather every source of income you received during the year. For most people, this means the wages on your W-2, but it also includes freelance or gig income (reported on 1099 forms), interest from bank accounts, dividends from investments, rental income, retirement distributions, and unemployment benefits. Add all of these together to get your gross income.
From gross income, you may subtract certain “above-the-line” adjustments to arrive at your adjusted gross income, commonly called AGI. These adjustments include contributions to a traditional IRA, student loan interest you paid (up to $2,500), and health savings account contributions. AGI matters because it determines your eligibility for many credits and deductions down the line.
Subtract Your Deductions
Once you have your AGI, you reduce it further by choosing either the standard deduction or itemized deductions, whichever is larger. Most taxpayers take the standard deduction because it requires no receipts or record-keeping. For tax year 2026, the standard deduction amounts are:
- Single or married filing separately: $16,100
- Married filing jointly: $32,200
- Head of household: $24,150
Itemizing makes sense only if your combined deductible expenses, such as mortgage interest, state and local taxes (capped at $10,000), charitable donations, and medical expenses above a certain threshold, exceed your standard deduction. If they don’t, take the standard deduction and move on.
The number you’re left with after subtracting deductions is your taxable income. This is the figure the IRS actually applies tax rates to.
Apply the Tax Brackets
Federal income tax uses a marginal system, meaning different portions of your income are taxed at different rates. You don’t pay a single flat rate on everything. Instead, your taxable income fills up each bracket in order, and only the income within that bracket is taxed at that bracket’s rate.
For example, here are the 2025 tax brackets for a single filer (2026 brackets had not been released at the time of writing):
- 10%: on the first $11,925
- 12%: on $11,926 to $48,475
- 22%: on $48,476 to $103,350
- 24%: on $103,351 to $197,300
- 32%: on $197,301 to $250,525
- 35%: on $250,526 to $626,350
- 37%: on $626,351 and above
Suppose you’re single with $65,000 in taxable income. You wouldn’t pay 22% on the entire $65,000. Instead, you’d pay 10% on the first $11,925 ($1,192.50), then 12% on the next chunk up to $48,475 ($4,386), then 22% only on the remaining amount from $48,476 to $65,000 ($3,635.50). Your total federal tax would be about $9,214, giving you an effective tax rate around 14.2%, well below the 22% bracket you technically fall into.
Subtract Credits From Your Tax Bill
This is where many people confuse credits and deductions. A deduction reduces your taxable income before the tax is calculated. A credit reduces the actual tax you owe, dollar for dollar, after the calculation. Credits are more valuable because $1,000 in credits saves you exactly $1,000, while $1,000 in deductions saves you only $1,000 times your tax rate (so $220 if you’re in the 22% bracket).
Common credits include the Child Tax Credit (up to $2,000 per qualifying child), the Earned Income Tax Credit for lower and moderate-income workers, the American Opportunity Credit for college expenses, and the Child and Dependent Care Credit. Some credits are “refundable,” meaning they can push your tax liability below zero and result in a payment to you even if you owe no tax. Others are “nonrefundable” and can only reduce your bill to zero.
After subtracting all eligible credits, you have your final tax liability for the year.
Compare What You Owe to What You Paid
This last step determines whether you get a refund or write a check. Look at Box 2 of your W-2, which shows how much federal income tax your employer withheld from your paychecks throughout the year. If you made estimated tax payments (common for freelancers and self-employed workers), add those in too.
If your total payments exceed your final tax liability, the difference is your refund. If your payments fall short, you owe the balance. That’s the entire calculation:
- Gross income minus adjustments equals AGI
- AGI minus deductions equals taxable income
- Taxable income run through the brackets equals your tax
- Tax minus credits equals your final tax liability
- Payments already made minus final tax liability equals your refund (or balance due)
A Worked Example
Say you’re a single filer who earned $55,000 in wages, contributed $2,000 to a traditional IRA, and has one qualifying child. Your employer withheld $4,800 in federal taxes over the year.
Your AGI is $53,000 ($55,000 minus the $2,000 IRA contribution). Subtract the 2026 standard deduction of $16,100, and your taxable income is $36,900. Running that through the brackets: 10% on the first $11,925 ($1,192.50) plus 12% on the remaining $24,975 ($2,997). Your tax before credits is $4,189.50.
Now apply the $2,000 Child Tax Credit, bringing your tax liability down to $2,189.50. You already paid $4,800 through withholding. Your refund would be $4,800 minus $2,189.50, or about $2,610.50.
Free Tools to Run the Numbers
You don’t have to do this math by hand. The IRS offers free filing options that handle the calculations automatically. If your adjusted gross income is $89,000 or less, you can use IRS Free File, which gives you access to guided tax preparation software at no cost. If you’re comfortable preparing your own return and want a bare-bones option, IRS Free File Fillable Forms are available to anyone regardless of income.
Commercial tax software walks you through each step with interview-style questions, filling in the brackets, deductions, and credits for you. Even if you plan to use software, understanding the math behind the calculation helps you spot errors and make smarter decisions about withholding, retirement contributions, and deductions throughout the year.