At a glance
Quick answer
The refund calculator compares named federal payments with a wage-only Form 1040 total tax estimate. Form W-2 box 1 wages enter federal income tax, while box 5 Medicare wages enter Additional Medicare Tax. The basic standard deduction is assumed. Payments include federal income tax withholding, Additional Medicare Tax withholding, Form 1040 line 26, and a Schedule 3 line 10 extension payment. Positive payments minus tax produce line 34 overpayment. Line 36 is subtracted to estimate the line 35a refund requested. Negative net produces line 37 amount owed, and zero is an exact balance.
How the calculation works
Keep Form W-2 box 1 and box 5 on separate paths
Enter taxpayer and valid joint spouse Form W-2 box 1 federal taxable wages for ordinary income. Enter box 5 Medicare wages separately for Additional Medicare Tax. The values can differ, so reusing one for both paths can change the result. For 2025, the IRS Tax Table applies below $100,000 of taxable income and the Tax Computation Worksheet applies at $100,000 or more. The 2026 selection uses planning brackets.
Apply only the basic standard deduction
The route uses the selected filing status's basic standard deduction. It excludes age and blindness amounts, dependent taxpayer limits, qualified business income, Schedule 1-A deductions, and itemized deductions. The result is labeled Basic standard deduction assumed.
Enter each supported federal payment once
Federal income tax withheld means Form W-2 box 2 plus federal income tax withheld on Forms 1099 and other records. Additional Medicare Tax withheld belongs in its separate Form 8959 line 24 field. Form 1040 line 26 contains confirmed estimated tax payments for the selected year plus a prior-year overpayment formally applied forward. A Form 4868 extension payment belongs only in the dedicated Schedule 3, line 10 field. Do not repeat it in line 26 or enter a Form 1040 line 31, 32, or 33 total.
Calculate overpayment before requested refund
The four supported payment amounts are added, then modeled Form 1040 total tax is subtracted. A positive signed result is Form 1040 line 34 overpayment. The entered Form 1040 line 36 amount applied to next year's estimated tax is subtracted from that overpayment to estimate the line 35a refund requested. Leaving line 36 blank assumes the full overpayment is requested as a refund. A negative signed result maps to line 37 amount owed, and zero is an exact balance. The 2025 instructions say an overpayment under $1 is refunded only on written request and a line 37 amount under $1 does not have to be paid.
Keep payment timing, penalties, and offsets separate
An amount owed does not prove an estimated tax penalty applies. Form 2210 compares timely payments with required installments. An overpayment does not prove every installment was timely. Treasury offsets can reduce the amount issued after the line 35a request. Penalties, interest, collection action, and safe harbor remain outside this arithmetic.
Move to the broader liability estimate when needed
Use records from every employer and payer. Joint filers should enter each spouse's box 1 and box 5 wages separately and combine federal withholding and payments. Use the broader federal income tax estimate when this wage-only scope is too narrow. That route estimates more liability components but does not reconcile payments, including withholding, line 26, an extension payment, or line 36.
2025 and 2026 values
Tax year 2025
2025 final return reconciliation
The final 2025 calculation uses the IRS Tax Table or Tax Computation Worksheet, a $15,750 single basic standard deduction assumed, and a $31,500 joint basic standard deduction assumed. Enter only payments credited to the 2025 federal return.
Tax year 2026
2026 planning return reconciliation
The 2026 planning calculation uses Revenue Procedure 2025-32 brackets, a $16,100 single basic standard deduction assumed, and a $32,200 joint basic standard deduction assumed. Payment entries and the line 36 allocation remain user-provided planning amounts.
Recalculate it yourself
Worked example
$40,090 of payments against $39,557 of total tax
A single filer has $210,000 in Form W-2 box 1 federal taxable wages, $210,000 in box 5 Medicare wages, $40,000 in box 2 federal income tax withholding, $90 of Additional Medicare Tax withheld from Form 8959, and no line 26 or extension payments for 2025.
- Ordinary taxable income = $210,000 box 1 wages − $15,750 basic standard deduction assumed = $194,250.
- Federal income tax after modeled credits = $194,250 × 24% − $7,153 Tax Computation Worksheet subtraction = $39,467.
- Additional Medicare Tax liability = ($210,000 box 5 Medicare wages − $200,000 single threshold) × 0.9% = $90, so modeled Form 1040 total tax = $39,467 + $90 = $39,557.
- Total entered federal payments = $40,000 federal income tax withholding + $90 Additional Medicare Tax withholding + $0 Form 1040 line 26 payments + $0 Schedule 3 line 10 extension payment = $40,090.
- Form 1040 line 34 overpayment = $40,090 total payments − $39,557 modeled total tax = $533.
- With $0 entered on Form 1040 line 36, the full $533 overpayment is assumed requested as the line 35a refund.
Result
The estimated Form 1040 line 35a refund requested is $533 before Treasury offsets. The result excludes age and blindness additions, dependent taxpayer limits, qualified business income, Schedule 1-A deductions, itemized deductions, omitted income, credits, penalties, interest, and state returns.
What is included
- Taxpayer and joint spouse Form W-2 box 1 federal taxable wages, separate box 5 Medicare wages, filing status, the basic standard deduction assumed, federal income tax, and supported Additional Medicare Tax liability.
- Federal income tax withholding, Additional Medicare Tax withholding, Form 1040 line 26 payments, Schedule 3 line 10 extension payment, line 34 overpayment, line 36 allocation, estimated line 35a refund requested, line 37 amount owed, and exact balance.
What is not included
- Regular Social Security and regular Medicare withholding, age and blindness additions, dependent taxpayer limits, itemized deductions, adjustments, qualified business income, Schedule 1-A deductions, nonwage and self-employment income, self-employment tax, qualified dividends, capital gains, Net Investment Income Tax (NIIT), AMT, and state or local returns.
- Refundable credits, unentered nonrefundable credits, other Schedule 3 payments, Form 2210 penalty computation, payment timing, late-payment penalties, interest, amended-return allocation, collection action, and Treasury refund offsets.
Common mistakes
Reusing box 1 as box 5
Form W-2 box 1 enters federal taxable wages and box 5 enters Medicare wages. The values can differ, so enter both from the form for each spouse.
Combining every payroll deduction as federal withholding
W-2 box 2 federal income tax withholding belongs in its field. Regular Social Security and regular Medicare withholding do not. Additional Medicare Tax withheld belongs in the separate Form 8959 field.
Counting an extension payment twice
Form 1040 line 26 is for estimated payments and a prior-year overpayment applied forward. Enter a Form 4868 extension payment only in the Schedule 3 line 10 field.
Calling line 34 the refund
Payments above tax produce Form 1040 line 34 overpayment. The line 36 amount applied to next year's estimated tax reduces the line 35a refund requested.
Treating the result as a penalty calculation
A year-end balance is not a Form 2210 result. Safe harbor amounts, installment dates, withholding timing, and special rules must be reviewed separately.
Assuming the requested refund is the issued refund
Credits, deductions, omitted income, penalties, interest, and Treasury offsets can change the amount filed or issued. A state refund is a separate calculation.
Frequently asked questions
What does the Tax refund calculator compare?
It compares supported Form 1040 total tax with federal income tax withholding, Additional Medicare Tax withholding, Form 1040 line 26 payments, and a Schedule 3 line 10 extension payment. Positive net payments produce a line 34 overpayment. The entered line 36 amount is then subtracted to estimate the line 35a refund requested.
What belongs in federal income tax withheld?
Enter W-2 box 2 amounts and federal income tax withheld on Forms 1099 or other records. Enter Additional Medicare Tax withheld from Form 8959, line 24, in its separate field.
Why does the calculator ask for both W-2 box 1 and box 5?
Form W-2 box 1 enters the wage-only federal income tax estimate. Box 5 enters the Additional Medicare Tax wage calculation. The amounts can differ, so the calculator does not reuse one for both.
Is the projected refund guaranteed?
No. The route assumes the basic standard deduction and excludes age and blindness additions, dependent taxpayer limits, qualified business income, Schedule 1-A deductions, itemized deductions, nonwage income, credits, penalties, interest, and Treasury offsets.
Does this calculate a state tax refund too?
No. The result is limited to the modeled federal return. State and local returns use separate rules, payments, credits, and filing systems.
Primary sources
- 2025 Instructions for Form 1040, opens in a new tab
Reviewed 2026-07-25
- 2025 Schedule 3 (Form 1040), Additional Credits and Payments, opens in a new tab
Reviewed 2026-07-25
- 2025 Form 8959, Additional Medicare Tax, opens in a new tab
Reviewed 2026-07-25
- 2025 General Instructions for Forms W-2 and W-3, opens in a new tab
Reviewed 2026-07-25
- IRS Revenue Procedure 2024-40, opens in a new tab
Reviewed 2026-07-25
- IRS Revenue Procedure 2025-32, opens in a new tab
Reviewed 2026-07-25
- IRS Questions and answers for the Additional Medicare Tax, opens in a new tab
Reviewed 2026-07-25
- IRS Topic 751, Social Security and Medicare withholding rates, opens in a new tab
Reviewed 2026-07-25
- 2025 Instructions for Form 2210, opens in a new tab
Reviewed 2026-07-24
- IRS Publication 505, Tax Withholding and Estimated Tax for 2025, opens in a new tab
Reviewed 2026-07-25