Tax Extension Calculator

Calculate balance due and penalties when filing a tax extension (Form 4868).
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$

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

This calculator helps you estimate the amount of tax you might owe when filing an extension. It's crucial because filing an extension only grants you more time to file your return, not more time to pay your taxes, preventing potential penalties and interest.

The calculator estimates your tax liability based on your reported income, deductions, and credits. It then subtracts any payments already made (e.g., withholding, estimated taxes) to determine your remaining tax due or potential refund.

A common mistake is assuming an extension means you don't have to pay anything. Always pay what you estimate you owe to avoid penalties. Overestimating your tax due is generally safer than underestimating.

Example: Samantha's Extension Estimate

  1. 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. 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. 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. 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?
No. Form 4868 extends only the filing deadline by 6 months (to October 15). You must still estimate and pay any tax owed by April 15 to avoid penalties and interest. An extension to file is not an extension to pay.
How do I file a tax extension?
File Form 4868 by April 15 electronically through IRS Free File, tax software, or a tax professional. You can also pay any estimated tax owed and mark it as an extension payment. The IRS automatically grants the extension upon receiving the form.
Will filing an extension increase my chances of an audit?
No. The IRS has stated that filing an extension does not increase audit risk. About 10-15 million taxpayers file extensions each year. It is better to file an extension than to rush and file an inaccurate return.

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