Table of Contents
Valor Tax Relief Team
Professional Tax Resolution Specialists
Published: October 11, 2026
Last Updated: October 11, 2026
Key takeaways
- No Q4 increase. On August 21, 2026, the IRS said Q4 rates match Q3, effective October 1 through December 31, 2026.
- Individuals at 7%. Underpayments and qualifying overpayments for non-corporate taxpayers stay at 7% per year, compounded daily.
- Most refunds earn no interest. The IRS typically pays interest only when a refund is late past the 45-day window after the filing deadline or your filing date.
- Corporate tiers. Corporations see 6% overpayments, 4.5% on large overpayment portions, 7% underpayments, and 9% on large corporate underpayments (LCU).
- Daily compounding. Unpaid balances still grow every day at the posted rate until you pay in full or resolve the debt another way.
- File even if you cannot pay. On-time filing avoids the larger failure-to-file penalty; an installment agreement can cut the failure-to-pay penalty rate when you qualify.
August 2026 IRS announcement
The IRS announced on August 21, 2026 that interest rates for the fourth quarter will not change. The new quarter starts October 1, 2026 and runs through December 31, 2026. The same percentages apply whether you owe tax or may receive interest on a qualifying delayed refund.
The posted rate tells you how fast an unpaid balance grows and whether you should pay sooner, set up a payment plan, or look at back tax relief before year-end.
Q4 2026 rate snapshot
The IRS keeps the same structure it used in the third quarter. Rates differ for individuals and corporations and depend on whether you underpaid or overpaid. All listed rates compound daily.
| Taxpayer type | Situation | Q4 2026 rate |
|---|---|---|
| Individual | Underpayment | 7% / year |
| Individual | Overpayment (qualifying) | 7% / year |
| Corporation | Overpayment | 6% / year |
| Corporation | Overpayment over $10,000 | 4.5% / year on excess |
| Corporation | Underpayment | 7% / year |
| Corporation | Large corporate underpayment (LCU) | 9% / year |
Rates for individual taxpayers
Individual taxpayers pay 7% on underpayments and receive 7% on qualifying overpayments for Q4 2026. That matches Q3. Because interest compounds daily, a balance left unpaid through the fall continues to increase even though the rate did not rise.
Refund interest is what most people ask about. Refunds the IRS sends on its usual timeline usually earn no interest. The IRS generally owes interest only when it does not issue your refund within 45 days after the later of two dates: the original due date of the return (without counting extensions) or the date you actually filed.
When refund interest may start
- Withholding and estimated tax: interest may run from the original due date if the refund is late.
- Late-filed returns: interest may start on your filing date instead of the original due date.
- Accrual generally continues until the IRS sends the refund.
For more detail on how the IRS computes interest on accounts, see our guide to IRS interest calculations.
Rates for corporate taxpayers
Corporations face a tiered schedule in Q4 2026, unchanged from the prior quarter. Overpayments earn 6% per year. The portion of an overpayment above $10,000 earns 4.5% on that excess. Underpayments are assessed at 7%, and large corporate underpayments (LCU) at 9%.
A large corporate underpayment generally means an underpayment above $100,000 for a tax period. The 9% LCU rate typically begins 30 days after the IRS sends its first letter proposing an adjustment or a notice of deficiency, whichever comes first.
Finance teams with large estimated tax gaps or audit adjustments should budget for these rates. Compare Q4 figures to earlier quarters in our Q2 2026 rate update if rates moved during the year.
How the IRS sets quarterly rates
The IRS updates interest every quarter using the federal short-term rate from the U.S. Treasury, plus fixed statutory margins that depend on taxpayer type and whether money is owed to or from the government.
For non-corporate taxpayers, both overpayment and underpayment rates equal the federal short-term rate plus 3 percentage points. Corporate underpayments use short-term plus 3 points; corporate overpayments use short-term plus 2 points. Large corporate underpayments add 5 points to the short-term rate. The corporate overpayment portion above $10,000 earns short-term plus 0.5 points.
The formulas stay fixed, but the published rate can move when the short-term rate moves. For Q4 2026, the IRS kept Q3 percentages in place based on the federal short-term rate calculated in July 2026.
What 7% means in practice
A flat quarter with no rate hike does not mean unpaid tax is cheap. Seven percent compounded daily still adds to the balance you see on IRS letters and account transcripts. The longer a debt sits, the more interest stacks on top of tax and penalties.
Taxpayers waiting on a refund may earn 7% only if they meet the late-refund rules. Most people who receive refunds on time will not see interest income from the IRS. Businesses with large liabilities or overpayments should still track how Q4 rates affect year-end planning.
Example: Nina owes $15,000 in tax from a prior year and makes no payments in Q4. Interest accrues at 7% compounded daily on the unpaid tax (and on other charges the IRS adds). Even partial payments reduce the base that interest hits next month.
Planning with Q4 rates in mind
With individual underpayment interest still at 7%, paying down balances sooner usually costs less than waiting. Partial payments help because interest applies to what remains unpaid.
File every required return on time even when you cannot pay in full. The failure-to-file penalty is generally much larger than the failure-to-pay penalty. An installment agreement can spread payments while you stay in compliance. Interest and the failure-to-pay penalty typically continue until the balance is zero, but the failure-to-pay penalty may drop to 0.25% per month while a qualifying installment agreement is in effect if you filed on time.
Businesses should review estimated tax deposits and audit reserves so Q4 underpayments do not trigger unnecessary LCU exposure. Owners who cannot pay in full may still qualify for penalty abatement or other programs depending on facts. Read how installment agreements work and underpayment penalties for related rules.
Estimated tax shortfalls can also trigger penalties separate from interest. Fixing withholding or quarterly payments for the current year helps you avoid new penalties while you work on older debt.
How Valor Tax Relief can help
If you owe more than you can pay this quarter, Valor can review your IRS account, explain how interest and penalties are adding up, and go over payment plans and other relief options.
We help taxpayers and business owners respond to notices, stay current on filing, and compare options while the balance is still manageable. Start with our FAQ hub or request a consultation through contact us.
Stable rates, rising balances
Q4 2026 brings no relief for taxpayers carrying debt: the individual 7% underpayment rate is unchanged, and daily compounding continues through December 31.
Use the quarter to file on time, make partial payments if you can, and set up a payment plan before the next rate announcement. Acting early usually leaves more choices than waiting until the balance grows.
Owe the IRS and watching interest add up?
Valor Tax Relief can review your balance and help you compare payment plans and relief options.
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