Invoice Late Fee Calculator
Calculate late payment fees and interest owed on an overdue Australian invoice using a flat fee, simple interest, compound interest or a mix.
Your results
Calculation breakdown
- Flat fee
- $1,000.00 × 5% = $50.00
- Simple interest
- $1,000.00 × 10% × 30/365 = $8.22
Assumptions
- Interest accrues on the original invoice amount only, not on any flat fee.
- A 365-day year is used for interest proration.
- Any late payment fee must be permitted by your contract or invoice terms to be legally recoverable.
Results are estimates only and are not financial, tax, legal or credit advice.
How this calculator works
Enter your invoice amount, days overdue and preferred fee structure to estimate the additional charge for late payment, whether that is a flat percentage fee, simple annual interest, compound annual interest, or a combination of a flat fee plus interest.
Frequently asked questions
Can I charge both a flat fee and interest?
Many contracts allow this, but the total charge must be reasonable and specified in your invoice terms or contract to be enforceable.
Does interest compound daily?
This calculator models simple interest (proportional to days overdue) or annually compounding interest prorated for the overdue period, not daily compounding.
Is there a legal cap on late fees in Australia?
Late fees must not be a 'penalty' under Australian contract law — they should reasonably reflect your actual loss, such as financing costs.
Results are estimates only and are not financial, tax, legal or credit advice.