A tax extension gives you more time to file your return, but not more time to pay
When you file Form 4868 (Application for Automatic Extension of Time To File U.S. Individual Income Tax Return), the IRS gives you six additional months to submit your tax return. That extension applies only to filing, not to payment. If you owe taxes, the deadline to pay remains April 15 of the year you file, regardless of whether you have an extension.
The consequence is straightforward: if you do not pay by April 15, the IRS charges interest on the unpaid balance starting the day after the original deadline passes. You also face a failure-to-pay penalty, which accrues monthly. Neither interest nor penalties stop just because your return is not yet filed. Filing an extension actually makes this worse, because you have six more months to owe money while interest compounds.
The only way to avoid interest and penalties is to pay what you estimate you owe by April 15, even if you have not finished your return. You can adjust the payment later when you file, but the clock on interest starts April 16 if you do not pay on time.
Key Takeaways
- Filing Form 4868 extends your filing deadline to October 15, but your payment deadline stays April 15 unless you have a valid reason for delay.
- Interest accrues at the federal rate (currently around 8 percent annually, but this changes quarterly) on any unpaid balance from April 16 onward.
- The failure-to-pay penalty is typically 0.5 percent of unpaid taxes per month, capped at 25 percent total, and runs separately from interest.
- If you cannot pay the full amount by April 15, you can set up a payment plan with the IRS, which stops the failure-to-pay penalty from growing but does not eliminate interest.
- Paying even a partial amount by April 15 reduces the balance that accrues interest, so paying something is better than paying nothing.
How interest and penalties stack when you file late but pay on time
If you file your return after April 15 but have already paid what you owe, you avoid both interest and the failure-to-pay penalty. You may still face a failure-to-file penalty if your return is more than 60 days late, but that penalty is smaller than the failure-to-pay penalty and applies only if you owe taxes.
This is why filing an extension and paying by April 15 is the standard move for people who need more time to gather documents or work with a tax professional. You get the time you need without the cost of interest and penalties. The failure-to-file penalty is 5 percent per month (up to 25 percent) for returns filed more than 60 days late, but it does not apply if you are due a refund.
What happens if you cannot pay by April 15
If you file an extension and cannot pay the full amount by April 15, you have options that reduce the damage. The IRS allows you to set up a payment plan (called an installment agreement) either before or after April 15. Short-term plans (120 days or fewer) have no setup fee. Long-term plans cost $31 to $225 depending on how you set it up.
Once you are on a payment plan, the failure-to-pay penalty drops from 0.5 percent per month to 0.25 percent per month. Interest still accrues on the unpaid balance, but the penalty slows. You can set up a plan online through IRS.gov, by phone at 1-800-829-1040, or through a tax professional.
If you pay part of what you owe by April 15 and set up a plan for the rest, interest applies only to the remaining balance. This is why paying anything before the deadline, even if it is not the full amount, reduces your total cost.
The difference between filing late and paying late
The IRS treats these as separate violations, and the penalties are different. A late filing (failure-to-file) penalty is 5 percent per month up to 25 percent. A late payment (failure-to-pay) penalty is 0.5 percent per month up to 25 percent. If you owe taxes and file late and pay late, both penalties apply, but the failure-to-pay penalty is the larger one.
If you file on time (using your extension) but pay late, you only face the failure-to-pay penalty and interest. If you pay on time but file late, you only face the failure-to-file penalty (and only if you file more than 60 days late). This is why the extension-plus-payment strategy works: you avoid the larger penalty by paying on time, even though you file later.
Interest rates and how they change
The IRS sets the interest rate quarterly based on the federal short-term rate plus 3 percent. As of early 2024, the rate is approximately 8 percent per year, but this changes every three months. The IRS publishes the current rate on IRS.gov under "Interest Rates."
Interest compounds daily. If you owe $5,000 and do not pay until October 15 (six months after the April 15 deadline), you will owe roughly $200 in interest alone, plus the failure-to-pay penalty. The longer you wait, the more interest accumulates. This is why paying as soon as possible, even if you have not filed yet, saves money.
How to estimate what you owe before filing
To pay by April 15, you need to know roughly what you owe. If you have already received a wage statement (W-2) or 1099 forms from your employer or clients, you can use those to estimate. Subtract your expected deductions from your income, multiply by your tax bracket, and compare to what you have already paid through withholding or estimated tax payments.
If you are unsure, it is better to overpay than underpay. Any overpayment becomes a refund when you file your return later. If you underpay, you owe interest on the shortfall. A tax professional can help you estimate in an hour or two, which is often worth the cost if you have a complex return.
When an extension might actually delay payment
In rare cases, the IRS may grant a delay in the payment deadline itself. This happens only if you request it separately from your filing extension and show financial hardship. You file Form 4868 for the filing extension, then contact the IRS to request a payment delay. The IRS rarely grants this, and it requires documented proof that you cannot pay.
If the IRS approves a payment delay, it may reduce or suspend the failure-to-pay penalty for the period of the delay, but interest still accrues. This is not automatic and should not be assumed. Most people who file an extension should plan to pay by April 15 regardless.
Frequently Asked Questions
If I file an extension, do I have until October 15 to pay?
No. Your payment deadline is still April 15. The extension gives you until October 15 to file your return, but if you owe taxes, you must pay by April 15 or face interest and penalties starting April 16. You can adjust your payment when you file in October if you overpaid or underpaid.
Can I avoid interest by filing an extension?
No. Interest is based on when you pay, not when you file. If you owe taxes and do not pay by April 15, interest starts accruing on April 16, even if you have an extension to file. Filing an extension does not stop interest from running.
What is the current interest rate on unpaid taxes?
The IRS sets the rate quarterly. As of early 2024, it is approximately 8 percent per year, but it changes every three months. Check IRS.gov for the current rate, which is published under "Interest Rates" and applies to the quarter in which your payment is due.
If I set up a payment plan, does interest stop?
No. Interest continues to accrue on the unpaid balance even after you set up a payment plan. However, the failure-to-pay penalty drops from 0.5 percent per month to 0.25 percent per month once you are on a plan, which reduces your total cost.
What happens if I pay part of what I owe by April 15?
Interest and penalties apply only to the unpaid portion. If you owe $10,000 and pay $6,000 by April 15, interest and the failure-to-pay penalty accrue only on the remaining $4,000. This is why paying anything before the deadline, even if incomplete, saves money.