Tax Extension Calculator
Calculate balance due and penalties when filing a tax extension (Form 4868).
By Konstantin Iakovlev · Updated April 2026 · Source: IRS — Forms, Instructions & Publications
Balance Due
$0.00
Penalty if Unpaid by Oct 15
$0.00
Total Owed by Oct 15
$0.00
Extension Details
| Estimated Tax | $0.00 |
| Already Paid / Withheld | $0.00 |
| Balance Due Now | $0.00 |
| Late Payment Penalty (6 mo) | $0.00 |
| Interest (6 mo) | $0.00 |
File Form 4868 by April 15 for automatic extension to October 15. Extension is to file, not to pay — interest and penalties accrue on unpaid balances.
Use the Tax Extension Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.
Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.
How It Works
Filing an extension pushes back the date your return is due, but the payment deadline does not move with it. Estimating what you are likely to owe before that original date passes is the key to staying clear of penalties and interest, and that is exactly the figure this tool helps you project.
The estimate starts from your reported income, then factors in your deductions and credits to arrive at an expected tax liability. From there it nets out what you have already paid in, whether through paycheck withholding or estimated tax installments, leaving either a remaining balance due or a projected refund.
The trap worth avoiding is treating an extension as permission to delay payment as well; paying your best estimate by the deadline keeps penalties at bay. When the exact number is uncertain, leaning toward a higher estimate is the safer side to err on, since paying slightly too much costs far less than coming up short.
Example: Samantha's Extension Estimate
- 1 Samantha estimates her total income for the year is $70,000. She anticipates $10,000 in deductions and $2,000 in tax credits. She has already had $8,000 withheld from her paychecks.
- 2 Inputting these figures: Estimated Income: $70,000. Estimated Deductions: $10,000. Estimated Credits: $2,000. Payments Made: $8,000. The calculator would then apply the relevant tax brackets to determine her estimated tax liability.
- 3 Based on her inputs and a hypothetical 15% estimated tax rate (after deductions), her estimated tax liability is $9,000. Subtracting her $8,000 in payments, she has an estimated tax due of $1,000.
- 4 Samantha should pay at least $1,000 by the original tax deadline to avoid penalties, even though she is filing an extension. She can then file her full return later.
Source: IRS — Forms, Instructions & Publications · Last updated: April 2026
Frequently Asked Questions
Does a tax extension give me more time to pay?
How do I file a tax extension?
Will filing an extension increase my chances of an audit?
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