Debt + Interest Calculator
Calculate the total amount you're owed including statutory interest. The standard rate in NSW is 9% per annum — adjust for your state below.
How interest is calculated
Statutory interest in Australia is calculated using simple interest: Principal × Rate × (Days Overdue ÷ 365). The standard rate in NSW is 9% per annum under the Civil Procedure Act 2005 (NSW). Other states may differ.
Interest typically runs from the date payment was due (or the date of the debt) to the date of judgment or payment. Including it in your letter of demand signals you know your rights.
Learn how to write a letter of demand →What the 2026 report says about waiting
Calculating interest is the easy part. The harder question is how long you can afford to wait before acting. Our 2026 Australian Debt Collection Report (Section 8) shows that the cost of waiting is not just the foregone interest — it's the sharp increase in debtor failure probability:
- A debtor with 1 formal trade default has a 20–24% probability of business failure within 12 months
- With 2 defaults: 42%
- With 3+ defaults: 62%
Once a debt enters formal insolvency, unsecured creditor returns collapse to less than 5 cents in the dollar on average (AFSA data). Interest accrued on an unpaid invoice is small consolation if the debtor enters liquidation. The 2026 report's recovery-rate ladder shows the letter of demand is the single highest-recovery, lowest-cost step you can take — 55–70% recovery rate at $29–$300 cost, typically resolved within 7–21 days. The economics of acting at day 30 past due rather than day 90 are unambiguous.
Include this amount in a formal letter
Send a lawyer-backed letter of demand with the exact amount owed — free, takes 5 minutes.
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