Penalty Interest Calculator

Choose the Relevant Method

This penalty interest calculator estimates interest on an overdue amount using manual rules or a Victorian preset. It compares full payment on the end date with an optional earlier payment. The example’s 10.5% rate is fictional.

Simple interest applies the daily rate to the original overdue amount for each counted day. Daily compound interest applies it to the growing balance, including previous interest. Moneysmart explains how simple and compound interest differ.

Under actual / 365, simple interest equals the overdue amount multiplied by the annual rate as a decimal, multiplied by counted days and divided by 365. Daily compound interest multiplies the balance by one plus the daily rate for every counted day. The calculation keeps precision until the displayed estimate is rounded to whole dollars.

Actual / actual divides the annual rate by 366 for each counted day in a leap year and 365 for other days. A period crossing a year boundary uses the denominator for each day’s own year. Weekends and public holidays count as calendar days.

The default excludes the start date and includes the end date. Other choices include both dates, exclude both dates or include the start and exclude the end. A same-day period counts one day only when you include both dates.

Choose Manual rate for a documented debt rule with one fixed annual rate. Its method, day basis and endpoint choices remain editable. Use each preset only for the named Victorian rule. The end-date breakdown applies the rate for each counted day and splits rows when that rate changes.

The Victoria statutory rate preset uses the Supreme Court of Victoria’s published penalty-interest schedule. It covers counted days from 1 Jun 2015 to 31 Oct 2026. The annual rate is 9.5% through 31 Jan 2017 and 10% from 1 Feb 2017. The preset estimates simple interest on an actual / 365 basis, excluding the start date and including the end date.

The Victorian Government’s fair-payments example uses the statutory rate with simple daily interest and a 365-day denominator. This preset supplies a rate calculation. The contract, court order or applicable law determines whether that rate applies and when interest starts. A contractual surcharge or separate penalty is outside the estimate.

For a stamp duty penalty interest calculation, choose Victoria stamp duty for ordinary late payment of Victorian land transfer duty. This preset uses the State Revenue Office’s interest rates. Counted days from 1 Jul 2025 to 30 Jun 2026 use 11.78%, comprising a 3.78% market rate and 8% premium. From 1 Jul 2026 to 30 Jun 2027, the total is 12.43%, comprising 4.43% plus 8%.

Enter the last day for payment as Start date and the full-payment day as End date. The duty preset excludes the start and includes the end, using simple daily interest divided by 365. Its supported periods contain no leap-year days. It applies the $20 minimum to the complete calculation: accrued interest below $20 gives a zero interest charge. Breakdown rows show accrued interest before that minimum.

The Taxation Administration Act 1997, sections 24-28 governs duty interest, its minimum and remission. The duty preset covers ordinary late-payment interest without remission. Repeated late payment, a tax shortfall, unpaid penalty tax or a remission decision can require a different calculation. Penalty tax is assessed separately, and this calculator adds none.

A preset refuses counted days outside its displayed schedule instead of extending the last rate. Use Manual rate for another documented fixed-rate rule. A period spanning other rate changes needs separate calculations for each rate period.

The estimate assumes no partial payments, fees, remissions or additional advances. It calculates an interest scenario and does not determine whether interest is legally payable. Confirm the debt’s terms and applicable rules before charging a client or explaining a final liability.

Compare Payment Timing

Earlier full payment reduces the days over which interest builds. Enter an earlier full-payment date within the selected period to compare both totals using identical calculation rules. Leave it empty when you need only the end-date estimate.

A fictional business owes $18,650. At a fictional 10.5% annual simple rate, the period from 1 Aug 2026 to 1 Oct 2026 counts 61 days when the start is excluded. With actual / 365, the displayed interest estimate is $327 and the amount plus interest is $18,977.

Full payment on 31 Aug 2026 counts 30 days under the same rules. The displayed earlier-payment interest is $161 and the earlier-payment total is $18,811. Paying then saves an estimated $166 of interest.

The earlier-payment total assumes settlement of the original amount and all interest then accrued. A partial payment needs a separate balance calculation. Entered amounts stay on this page and are neither sent to Tax Genie nor saved in browser storage.