Late Payment Interest Calculator
Calculate interest on overdue construction payments using simple daily interest.
General tool only. This calculator gives estimates based on the values you enter. Always check your contract terms and any state-specific rules before relying on the figures.
Interest entitlement and rate depend on your contract and applicable state rules. Confirm before relying on the result.
Results
Enter the overdue amount, rate and dates to calculate interest.
How it works
Behind the numbers
The calculator uses simple daily interest. Many AU contracts fix the interest rate (e.g. RBA cash rate plus a margin) — check yours before relying on the figure.
Interest entitlement and rate depend on your contract and the relevant state Act. This tool is general only.
Formula
The maths, written out
Days = Payment date − Due date Interest = Amount × (Rate% ÷ 365) × Days Total = Amount + Interest
Worked example
A quick scenario
$38,500 overdue 45 days at 11.95% p.a. accrues $567.22 in interest = $39,067.22 total.
Frequently asked
Is this calculator free to use?
Yes. All calculators on Contractor Calc are free and do not require sign-up.
How accurate are the results?
The calculators use standard formulas. Results are estimates only and depend on the values you enter. Always check against your contract.
Can I export the results?
Most calculators include a download or copy-to-clipboard option for sharing with clients or storing in your records.