The IRS charges interest on unpaid taxes, and that interest keeps running while you're on a payment plan

If you set up an IRS payment plan (also called an installment agreement), you still owe interest on the full amount of tax you didn't pay on time. The IRS doesn't reduce the interest rate because you're paying in installments — you pay the same interest rate whether you settle the bill in one payment or spread it over months or years.

The interest rate itself changes quarterly. The IRS sets it based on the federal short-term rate plus 3 percentage points. This means the rate you're charged depends on when you set up your plan. As of early 2024, the rate has ranged between roughly 8% and 10% annually, but you should check the current rate on the IRS website or ask when you contact them about a plan.

Beyond interest, the IRS also charges a failure-to-pay penalty — usually 0.5% of your unpaid tax per month, up to 25% total. This penalty also continues while you're on a payment plan. Together, interest and penalties can add thousands of dollars to what you originally owed.

Key Takeaways

  • Interest accrues on the full unpaid tax balance at a rate set quarterly by the IRS, currently in the 8–10% range annually.
  • The interest rate does not change based on your payment plan — you pay the same rate whether you pay in full or over time.
  • A failure-to-pay penalty of 0.5% per month (up to 25% total) also applies and continues while you're on a plan.
  • The longer your payment plan, the more interest and penalties you will owe in total, even though your monthly payment stays the same.
  • You can check the current interest rate on the IRS website or ask the IRS when you set up your plan.

How the interest rate is set and when it changes

The IRS publishes a new interest rate every three months, on the 1st of January, April, July, and October. The rate is the federal short-term rate (set by the U.S. Treasury) plus 3 percentage points. Because the federal rate moves with economic conditions, the IRS rate moves too — it goes up when the economy heats up and down when it cools.

If you're already on a payment plan, your rate does not automatically change when the IRS announces a new quarterly rate. The rate you locked in when you set up your plan stays the same for the life of that plan. If you set up a new plan later, you'll get whatever the current rate is at that time.

The IRS publishes current and historical rates on its website under "Interest Rates." You can also call the IRS at 800-829-1040 and ask what the current rate is before you commit to a plan.

Interest versus penalties: what you're actually paying

Your total cost on a payment plan includes two separate charges: interest and penalties. Many people focus on the interest rate and miss the penalty, which can be just as expensive.

The failure-to-pay penalty is 0.5% of your unpaid tax per month, starting the day after your tax return was due. It maxes out at 25% of the unpaid tax. So if you owed $10,000 and didn't pay it, you'd owe an additional $5,000 in penalties alone (25% of $10,000) by the time the penalty stops accruing. That happens 50 months after the due date — roughly four years.

Interest is separate and continues indefinitely until you pay. It compounds daily on the unpaid tax plus any penalties. On a $10,000 debt at 9% annual interest, you'd owe roughly $900 in interest in the first year alone, and more each year after that if you're still paying.

How much longer a payment plan costs you

The longer you stretch out your payments, the more interest you pay overall. Your monthly payment might be lower, but the total cost climbs.

Here's a concrete example: if you owe $5,000 in tax and the current interest rate is 9%, paying it off in 12 months costs roughly $225 in interest. Stretching it to 36 months costs roughly $700 in interest — nearly three times as much. The monthly payment drops from about $427 to about $155, but you're paying an extra $475 in interest for that convenience.

The IRS offers several plan lengths: short-term plans (120 days or less), standard plans (up to 72 months), and long-term plans (up to 84 months for larger debts). The longer the plan, the lower your monthly payment — but the higher your total interest cost.

Payment plan types and their interest charges

The IRS offers different kinds of payment plans, and interest applies to all of them the same way. The plan type affects your monthly payment and setup fees, not the interest rate.

A short-term plan (120 days or less) has no setup fee and lets you pay in a few installments. Interest still accrues daily. A standard installment agreement (the most common type) lets you pay over up to 72 months and costs $225 to set up. A direct debit installment agreement (where the IRS automatically withdraws from your bank account each month) costs $31 to set up and often qualifies you for a slightly lower interest rate — but the difference is small, usually a quarter-point or less.

No matter which plan you choose, interest runs at the same quarterly rate. The only way to reduce interest is to pay off the debt faster.

What happens if you can't afford the monthly payment

If your payment plan payment becomes unaffordable, you can ask the IRS to modify it — usually by extending the timeline to lower the monthly amount. Extending the plan means more interest accrues, but it keeps you in compliance and stops the IRS from taking collection action like wage garnishment or bank levy.

You can also ask for a temporary pause on payments if you're in financial hardship. The IRS calls this "currently not collectible" status. Interest and penalties still accrue during the pause, but you're not required to make monthly payments. Once your situation improves, the IRS will contact you to restart the plan.

If you think you might not be able to stick to a plan, be honest about it when you set it up. The IRS would rather work with you on a realistic payment schedule than have you default and face collection action.

How to find out the exact interest you'll owe

The IRS doesn't publish a simple calculator for total interest on a payment plan, but you can estimate it yourself or ask the IRS directly. When you contact the IRS to set up a plan, they'll tell you the current interest rate and can calculate roughly how much interest you'll owe over the life of the plan you're considering.

You can also use a basic loan calculator (search "loan interest calculator") and plug in your tax debt as the principal, the current IRS rate as the interest rate, and your proposed plan length as the loan term. The result won't be exact — the IRS compounds interest daily, not monthly — but it will be close enough to compare plan options.

The IRS website has a payment plan estimator tool that shows monthly payment amounts for different plan lengths. It doesn't calculate total interest, but it helps you see the trade-off: lower monthly payment versus higher total cost.

Frequently Asked Questions

Does the IRS charge interest on penalties?

Yes. Interest accrues on the unpaid tax, the failure-to-pay penalty, and any other penalties the IRS has assessed. So interest compounds on top of penalties, making the total debt grow faster than the original tax alone.

Can I negotiate a lower interest rate on my payment plan?

No. The interest rate is set by law and applies to all taxpayers equally. The only way to reduce the total interest you pay is to pay off the debt faster or to set up a direct debit plan, which may may have access to you for a rate reduction of about 0.25 percentage points.

What if I pay off my plan early?

You can pay off a payment plan at any time without penalty. Interest stops accruing on the day you pay the final balance. Paying early saves you money on interest, though you'll still owe any interest that accrued up to that point.

Does the interest rate change if I'm on a payment plan for several years?

No. The interest rate you're charged when you set up your plan stays the same for the entire life of that plan, even if the IRS's quarterly rate changes. If you set up a new plan later, you'll get the rate that's current at that time.

What's the difference between interest and the failure-to-pay penalty?

Interest is a daily charge on your unpaid balance. The failure-to-pay penalty is a separate monthly charge (0.5% per month, up to 25% total) that applies because you didn't pay by the due date. Both apply on a payment plan, and both add to what you owe.