Interest and penalties are added to what you owe, not included in your monthly payment
When you set up an IRS payment plan, your monthly payment covers only the tax itself. The IRS charges interest on the unpaid balance every day until it is paid in full, and penalties on top of that. These costs are separate from your payment amount and continue to grow month to month. You do not choose to pay them—they are calculated automatically and added to your debt.
The interest rate is set by federal law and changes quarterly. As of early 2024, the rate is 8 percent per year, but this shifts every three months based on the federal short-term rate. The IRS publishes the current rate on its website. Penalties depend on why you owe: if you filed late, you pay a failure-to-file penalty; if you did not pay on time, you pay a failure-to-pay penalty. Both are calculated as a percentage of the unpaid tax.
The longer your payment plan runs, the more interest and penalties accumulate. A payment plan that stretches over three years will cost significantly more than one paid off in six months, even though your monthly payment stays the same. This is why understanding the total cost matters before you commit to a plan.
Key Takeaways
- Interest accrues daily on your unpaid tax balance at a rate set by federal law and updated quarterly, currently around 8 percent per year.
- Penalties are added separately and depend on whether you filed late, paid late, or both—they are not negotiable and continue until the debt is paid.
- Your monthly payment amount does not change, but interest and penalties keep growing, so the total cost rises the longer the plan lasts.
- You can see the exact interest rate and penalty amounts on your IRS notice or by calling the IRS at 800-829-1040.
How the IRS calculates interest on your balance
Interest is calculated as a daily rate applied to whatever you still owe. The IRS divides the annual rate by 365 days, then multiplies that by your unpaid balance each day. If your balance is $5,000 and the rate is 8 percent annually, you owe roughly $1.10 per day in interest alone. That $1.10 is added to your balance, so the next day's interest is calculated on $5,001.10, and so on.
The interest rate itself is tied to the federal short-term rate plus 3 percentage points. The IRS announces the new rate on its website each quarter—January, April, July, and October. If rates change mid-payment plan, your interest rate changes too. You will not see a jump in your monthly payment, but the interest portion of what you owe will shift, meaning more of your payment goes toward interest and less toward the principal.
Interest stops accruing only when the full balance is paid. If you pay off your plan early, you save on interest because fewer days pass. If you miss a payment or fall behind, interest continues to accrue on the missed amount as well as the original balance.
Penalties that stack on top of interest
The IRS imposes two main penalties on unpaid tax: the failure-to-file penalty and the failure-to-pay penalty. If you did not file your return by the important date, you owe 5 percent of the unpaid tax for each month (or part of a month) that the return was late, up to 25 percent total. If you filed on time but did not pay, you owe 0.5 percent of the unpaid tax for each month the payment is late, also capped at 25 percent.
If you both filed late and paid late, both penalties explore. A $10,000 debt with both penalties could add $2,500 in penalties alone before interest is calculated. These penalties are not waived on a payment plan—they are part of your total debt from day one.
The IRS can reduce or remove penalties in limited cases if you have a reasonable cause—for example, a serious illness, a death in the family, or reliance on a tax professional's bad information. You would need to request this relief in writing and provide documentation. Most people on payment plans do not receive penalty relief, so plan on paying the full amount.
What a payment plan costs over time
The total cost of a payment plan depends on three things: the amount you owe, the interest rate, and how long the plan lasts. Here is a realistic example:
| Unpaid Tax | Plan Length | Monthly Payment | Total Interest (Approx.) | Total Cost |
|---|---|---|---|---|
| $5,000 | 12 months | $417 | $200 | $5,200 |
| $5,000 | 24 months | $208 | $400 | $5,400 |
| $5,000 | 36 months | $139 | $600 | $5,600 |
These are approximations because interest rates can change and penalties may vary. The point is clear: doubling the plan length does not double the cost, but it does add hundreds of dollars in interest. If you can afford a shorter plan, you will pay less overall.
Short-term plans versus long-term plans
The IRS offers two main types of payment plans: short-term (up to 180 days) and long-term (installment agreements lasting years). Short-term plans have a lower setup fee—currently $31 if you set it up online—and accrue less interest because the debt is paid faster. Long-term plans cost more to set up ($225 for a standard agreement, $31 if you use direct debit) and accrue significantly more interest over time.
If you owe less than $50,000, you can request a long-term plan lasting up to six years. If you owe more, the IRS may require a longer plan or a different arrangement. The monthly payment is lower on a longer plan, but you pay more in total interest. Before choosing a plan length, calculate what you can actually afford each month—missing payments triggers penalties and can end the agreement.
How to find out your exact interest and penalty amounts
The IRS notice you received (usually a CP notice or a bill) shows your tax balance, penalties, and interest as of the date the notice was issued. Call the IRS at 800-829-1040 to speak with a representative who can tell you the current balance, including interest accrued since the notice was sent. Have your Social Security number and the tax year in question ready.
You can also view your account online through the IRS website if you have an account set up. The transcript shows your balance and breaks down penalties and interest separately. If you are working with a tax professional or enrolled agent, they can request a detailed account transcript on your behalf.
When you set up a payment plan, the IRS will show you the total amount due and the monthly payment. Interest will continue to accrue during the plan, so the final payment may be slightly higher than the earlier ones, or the last payment may be smaller if you overpay slightly along the way.
What happens if you pay off the plan early
Paying off your plan early saves you money because interest stops accruing. If you have a lump sum available—a tax refund, a bonus, an inheritance—you can explore it to your IRS debt and reduce the remaining balance. The interest you would have paid on that amount over the remaining months is eliminated.
There is no penalty for early payment. You can pay more than your monthly amount at any time without triggering extra fees. Contact the IRS or your payment plan servicer to confirm that extra payments are applied to the principal, not held in a suspense account.
Frequently Asked Questions
Can the IRS reduce the interest rate on my payment plan?
No. Interest is set by federal law and applies to all taxpayers equally. The IRS cannot lower it, and you cannot negotiate it. The rate changes quarterly based on the federal short-term rate, but you have no control over that change.
Will the IRS remove my penalties if I set up a payment plan?
Not automatically. Penalties remain part of your debt. You can request penalty relief by submitting Form 843 (Claim for Refund and Request for Abatement) with documentation of reasonable cause—serious illness, death, or reliance on a tax professional's error are examples. Most requests are denied, so do not count on relief.
What if I miss a payment on my plan?
Missing a payment can end your agreement and trigger a failure-to-pay penalty on the missed amount. Interest continues to accrue on everything you owe. Contact the IRS when ready if you cannot make a payment—they may allow you to catch up or modify the plan rather than defaulting.
Does the interest rate change while I'm on a payment plan?
Yes. The IRS updates the interest rate quarterly. If the rate goes up, your interest accrual increases, but your monthly payment stays the same. If the rate goes down, your interest accrual decreases. Either way, interest continues until the debt is paid in full.
How much will I pay in total interest on a three-year plan?
It depends on the amount you owe and the interest rate during those three years. For a $10,000 debt at 8 percent interest over 36 months, you would pay roughly $1,200 to $1,400 in interest, plus any penalties. Use an online calculator or call the IRS for a specific estimate based on your balance.