If you don’t file a tax extension and don’t file your return by April 15, 2026, the IRS starts charging a failure-to-file penalty of 5% of your unpaid tax the day after the deadline, and it keeps adding 5% every month until it reaches 25%. Interest starts running the same day. Filing Form 4868 by April 15 would have given you six more months to submit paperwork, but even an extension never extends the time to pay. The single most useful thing you can do now is file the return, even if you can’t pay the balance.
The Failure-to-File Penalty
The IRS charges 5% of your unpaid tax for every month, or partial month, your return is late. One day past the deadline triggers the first 5%. The penalty caps at 25% of the unpaid balance, which it reaches after five months.1Office of the Law Revision Counsel. 26 U.S.C. 6651 – Failure to File Tax Return or to Pay Tax
Once your return is more than 60 days late, a minimum penalty kicks in. It’s the lesser of $535 or 100% of the unpaid tax. That floor is adjusted for inflation.2Internal Revenue Service. Rev. Proc. 2025-32 – Inflation Adjusted Items On a small balance, that minimum can equal the whole tax bill.
The penalty is calculated against tax still owed at the filing deadline. If withholding or estimated payments already covered your liability, there’s no failure-to-file penalty even if the return shows up late. The IRS won’t know that, though, until you file.
The Failure-to-Pay Penalty
A second penalty runs on any balance unpaid after April 15. It accrues at 0.5% per month, or partial month, and also caps at 25%.1Office of the Law Revision Counsel. 26 U.S.C. 6651 – Failure to File Tax Return or to Pay Tax At that pace, hitting the ceiling takes roughly four years.
One discount is worth knowing. If you filed the return on time and set up an IRS payment plan, the failure-to-pay rate drops to 0.25% per month while that plan is active.3Internal Revenue Service. Failure to Pay Penalty Missing the filing deadline forfeits that half-rate.
How the Penalties Combine
When both penalties apply in the same month, the IRS doesn’t simply add them. The failure-to-file penalty is reduced by the failure-to-pay amount for overlapping months, so the combined charge works out to 4.5% for not filing plus 0.5% for not paying, or 5% per month.3Internal Revenue Service. Failure to Pay Penalty
After five months, the failure-to-file portion hits its 25% ceiling and stops. The failure-to-pay penalty keeps growing at 0.5% per month until it reaches its own 25% cap or the balance is paid. Total exposure from the two penalties combined tops out at 47.5% of the original unpaid tax, before interest.1Office of the Law Revision Counsel. 26 U.S.C. 6651 – Failure to File Tax Return or to Pay Tax
The failure-to-file penalty is ten times the failure-to-pay rate. If you can’t pay the whole balance, file the return anyway. Skipping it entirely is the most expensive option.
Interest Runs Separately
On top of the penalties, the IRS charges interest on unpaid tax starting the day after April 15. Interest compounds daily.4Office of the Law Revision Counsel. 26 U.S. Code 6622 – Interest Compounded Daily
The rate is set quarterly and equals the federal short-term rate plus three percentage points.5Office of the Law Revision Counsel. 26 U.S. Code 6621 – Determination of Rate of Interest For the first quarter of 2026, the rate is 7%.6Internal Revenue Service. Rev. Rul. 2025-22 – Quarterly Interest Rates
Interest cannot be waived. The IRS has no discretion to reduce or remove it, even with a good reason for paying late. And interest accrues on the penalties themselves, not just the tax, which is how a modest bill can quietly double over a few years.7Office of the Law Revision Counsel. 26 U.S.C. 6601 – Interest on Underpayment, Nonpayment, or Extensions of Time for Payment, of Tax
If You Simply Never File
Ignoring the return doesn’t stop the process. The IRS can prepare a substitute return using income reported by employers, banks, and brokerages. That substitute will almost always overstate what you owe, because the IRS applies only the standard deduction. No itemized deductions, no child tax credit, no business expenses.8Internal Revenue Service. 4.12.1 Nonfiled Returns
Then comes a Notice of Deficiency, also called a 90-day letter. You have 90 days from its mailing date to petition the U.S. Tax Court without paying first. Miss that window and the tax is assessed as proposed.9Internal Revenue Service. Filing Past Due Tax Returns
You can still replace a substitute return by filing your own, even years later, and usually reduce the balance by claiming the deductions and credits the IRS left out. The penalties and interest already accumulated don’t disappear.
Civil penalties are the usual consequence. Willfully refusing to file is also a federal misdemeanor carrying a fine of up to $25,000 and up to one year in prison.10Office of the Law Revision Counsel. 26 U.S. Code 7203 – Willful Failure to File Return, Supply Information, or Pay Tax Willfully means a deliberate choice to skip filing, not an oversight. Prosecution is rare and generally reserved for high-income taxpayers who ignore the obligation year after year.
If You’re Owed a Refund
If the IRS owes you money, none of the penalties above apply. There’s still a deadline, though. You have three years from the original filing date to submit the return and collect the refund.11Office of the Law Revision Counsel. 26 U.S.C. 6511 – Limitations on Credit or Refund
After three years, the overpayment goes to the U.S. Treasury permanently. No appeal, no extension. Someone who skips filing on the assumption they’re getting a refund, and then lets a few years go by, can lose the money entirely.
Getting the Penalties Reduced
Interest is fixed, but both penalties can be reduced or removed through two channels.
First-Time Abatement
If you filed all required returns for the prior three tax years and had no penalties assessed during that period, you can request a one-time waiver of the failure-to-file or failure-to-pay penalty. The IRS calls this First Time Abate and treats it as an administrative courtesy.12Internal Revenue Service. Administrative Penalty Relief Calling the number on your penalty notice is often enough; a representative may approve it on the call. If denied by phone, you can submit Form 843 in writing.13Internal Revenue Service. Penalty Relief
Reasonable Cause
If first-time abatement isn’t available, you can ask for relief by showing a valid reason for filing or paying late. The IRS considers natural disasters, serious illness or death in the immediate family, inability to obtain records, and electronic-filing system failures.14Internal Revenue Service. Penalty Relief for Reasonable Cause Forgetting or being busy won’t work. You’ll need a written explanation and, where possible, supporting documents like hospital or insurance records.
File Now, Even If You Can’t Pay
The IRS would rather work with a filer on payments than chase someone who hasn’t filed. If your balance is under $50,000 combined, you can apply online for a long-term monthly installment plan. Balances under $100,000 qualify for a short-term plan giving up to 180 days to pay in full.15Internal Revenue Service. Payment Plans; Installment Agreements Filing on time and setting up a plan cuts the failure-to-pay rate in half; filing late gives that up but still puts the plan machinery within reach.
You can submit a late return through the IRS e-file system or by mail. Electronic filing gives you instant confirmation, which matters because timing affects the penalty calculation. If a notice has already arrived, send the return to the address on that notice rather than the standard processing center.9Internal Revenue Service. Filing Past Due Tax Returns The IRS will then send a notice showing the penalties and interest assessed, with instructions for paying or requesting a plan. If the assessment rests on a substitute return that overstated your income, filing your own complete return is the first step toward correcting it.