Debt + Interest Calculator
Estimate what an overdue invoice is worth today, including interest. Enter the interest rate your contract provides for — if it doesn't provide for one, leave it at zero.
Can you actually charge interest?
This is the question to settle before you put an interest figure in front of a debtor. Broadly, there are two ways interest becomes payable:
- Your contract says so. If your terms of trade or signed contract include an interest clause, that clause sets the rate and when it starts running.
- A court awards it. If a matter goes to judgment, a court may award pre-judgment interest. In NSW that discretion sits under the Civil Procedure Act 2005 (NSW), and the rate is set by Practice Note rather than being a fixed figure.
If neither applies, you generally have no entitlement to interest, and claiming it anyway risks overstating what you are owed. The calculation itself is simple interest: Principal × Rate × (Days Overdue ÷ 365).
This calculator produces an estimate from the figures you enter. It does not tell you what you are legally entitled to claim. SydneyCollect is not a law firm and this is general information, not legal advice.
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.
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