IRS interest and refund calculator
Estimates the interest the IRS charges on late/underpaid tax — or pays on your refund — using the real method: the quarterly §6621 rate in force each day, compounded daily under §6622, across every rate change on record (back to 2017).
Estimate for reference only — courts, agencies and creditors may apply different rounding or conventions. Not legal, tax, or financial advice.
Current 2026 IRS interest rates
The calculator automatically changes rates at each quarter boundary. The latest recorded references are:
| IRS interest category | Current rate | Effective | History |
|---|---|---|---|
| Underpayment | 7% | July 1, 2026 | 39 recorded quarters |
| Refund / individual overpayment | 7% | July 1, 2026 | 39 recorded quarters |
| Corporate overpayment | 6% | July 1, 2026 | 39 recorded quarters |
| Large corporate underpayment | 9% | July 1, 2026 | 39 recorded quarters |
How it works
IRS interest rates reset every calendar quarter — the underpayment rate is currently 7% — and interest compounds daily: each day's interest is added to the balance before the next day's is computed. This calculator walks day-by-day through your date range, applying the correct quarter's rate (365- or 366-day years handled), which matters whenever a balance spans a rate change.
For failure-to-file and failure-to-pay charges, use the separate Form 1040 penalty and interest calculator. Estimated-tax additions under §§6654/6655 are not covered; they use the underpayment rate but as simple interest. The IRS computes official amounts with its Rev. Proc. 95-17 factor tables, so small rounding differences are possible.
Calculating interest on an IRS refund
Select Overpayment — individual when the IRS owes interest to a person, or the corporate overpayment option for a corporation. Enter the overpayment principal and the applicable interest period. The calculator segments the period by calendar quarter, applies every recorded rate change, and compounds daily. The IRS controls the legal start date and may apply statutory waiting periods, so confirm the dates against the notice or refund rules that apply to the return.
Frequently asked questions
How does the IRS calculate interest on unpaid taxes?
The IRS applies the §6621 rate for each calendar quarter (federal short-term rate plus 3 points for most taxpayers) and compounds it daily under §6622. Because the rate resets quarterly, a balance that spans several quarters accrues at several different rates.
Does the IRS pay interest on refunds?
Yes — overpayments accrue interest at the §6621 overpayment rate (the same as the underpayment rate for individuals and one point lower for corporations), also compounded daily.
How do I calculate IRS interest on a delayed tax refund?
Choose the individual or corporate overpayment series, enter the overpayment amount and applicable start and end dates, and the calculator applies each quarterly §6621 rate with §6622 daily compounding.