UK Tax Tools

HMRC Interest Calculator

Work out exactly how much HMRC interest is due on a late tax payment, or how much interest HMRC owes you back on an overpayment — simple daily interest, split automatically across every rate period your dates span.

Total to pay

£5,063.70

£5,000.00 + £63.70 interest

Late payment interest

£63.70

60 days at 7.75% average

Days outstanding

60

Simple daily interest, 365-day year

Your dates and amount

HMRC's late payment interest rate — what it charges on unpaid Self Assessment, PAYE, VAT, Corporation Tax or CGT.

The statutory due date for the tax in question (e.g. 31 January for a Self Assessment balancing payment).

Still outstanding? Leave today's date to see where you stand right now.

Interest breakdown — £63.70

Simple daily interest on £5,000.00 at HMRC's published rate for the period.

PeriodDaysRateInterest
26 June 2026 – 24 August 2026607.75%£63.70

Rates come from the HMRC interest rate table, sourced from gov.uk.

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How this calculator works

HMRC interest is simple, not compound — it's calculated on the original amount only, never on interest already accrued. The formula is amount × annual rate ÷ 100 × days ÷ 365, applied daily from the day after the due date until the date of payment.

Because the Bank of England base rate moves, so does HMRC's published rate — roughly two to four weeks after each Monetary Policy Committee decision. If your due date and payment date fall either side of one of these changes, this calculator doesn't apply a single average rate to the whole period; it splits the calculation at each boundary and charges every day at whichever rate was actually in force, exactly as HMRC does. See the HMRC interest rates page for the full rate history this calculator reads from.

Late payment vs repayment interest

HMRC runs two separate interest rates, both derived from the Bank of England base rate but moving in opposite directions from it:

  • Late payment interest — base rate + 4 percentage points, currently 7.75%. Charged on tax you pay late.
  • Repayment interest — base rate − 1 percentage point (floored at 0.5%), currently 2.75%. Paid to you on tax HMRC owes back.

The gap is deliberate: HMRC charges more for late payment than it pays for repayment, so there's no advantage to treating unpaid tax as free credit. This calculator covers both — switch modes above to see which applies to your situation. If your Self Assessment return was also filed late, the interest here can be combined with the separate filing and payment penalties on the Self Assessment Penalty Calculator.

Frequently asked questions

How does HMRC calculate late payment interest?
HMRC charges simple (non-compounding) interest, accruing daily on a 365-day year: amount owed × the published annual rate × number of days ÷ 365. It runs from the day after the tax was due until the date it's paid in full. If the rate changes while the bill is outstanding, each day is charged at whichever rate was in force that day, not one blended rate for the whole period.
What is the current HMRC late payment interest rate?
The current HMRC late payment interest rate is 7.75%, effective from 9 January 2026. It's set at the Bank of England base rate plus 4 percentage points and applies to unpaid Self Assessment, PAYE, VAT, Corporation Tax and Capital Gains Tax. See the full rate history on the HMRC interest rates page.
What is HMRC repayment interest and how is it different?
Repayment interest is what HMRC pays you when it owes you money — most often a Self Assessment refund or an overpaid payment on account. It's calculated the same way (simple daily interest on a 365-day year) but at a lower rate: the Bank of England base rate minus 1 percentage point, floored at 0.5%. The current repayment rate is 2.75%.
Does interest stack with HMRC penalties?
Yes. Interest and penalties are separate and both can apply at the same time. Interest simply compensates HMRC (or you) for the time value of money and has no fixed cap — it keeps running until the balance is settled. Penalties are additional fixed or percentage charges for lateness itself. For a Self Assessment bill that's also late filed, use the Self Assessment Penalty Calculator to see the full penalty ladder alongside interest.
What date should I use as the due date?
Use the statutory due date for the tax in question — 31 January for a Self Assessment balancing payment or the first payment on account, 31 July for the second payment on account, or the relevant PAYE/VAT/Corporation Tax deadline. Interest starts accruing the day after that date, not the day of it.
Can this calculator handle a debt that spans a rate change?
Yes — that's the main reason to use a calculator rather than a single flat-rate estimate. Enter your due date and payment date and the calculator automatically splits the interest across every HMRC rate period in between, using each period's own rate, then totals the result. The breakdown table shows exactly how many days were charged at each rate.

Sources

Related Calculators

HMRC Interest Rates

Current HMRC late payment and repayment interest rates plus the full history since 2022.

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Work out HMRC's full filing and payment penalty ladder plus interest for a late Self Assessment return.

Payment on Account Calculator

Work out your 31 January and 31 July payments on account, and model late-payment interest and penalties.

Tax Refund Estimator

Check if you're owed a Self Assessment refund from HMRC.

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