Accountants Late Payment Interest (Hourly) Calculator FAQ
Answers to common questions about hourly invoice interest calculations, inputs, assumptions, and estimated results.
This FAQ explains what the hourly late payment interest calculator does, how its inputs work, and why an estimate can differ from an amount claimed or agreed in practice.
General questions
Basic information about the calculator and its purpose.
What does the calculator calculate?
It estimates simple interest on an unpaid accountancy invoice for a late period measured in full days and additional hours.
Who can use this calculator?
It can be used to model an overdue accountancy or professional-services invoice when a rate and overdue period are known.
Is the total amount due the same as the invoice balance?
No. It is the invoice balance plus estimated interest only.
Rates and time
How annual rates and overdue time are used.
What annual rate should I enter?
Use the rate stated in the applicable agreement or otherwise relevant to your situation. This calculator does not select a rate for you.
Why are days and additional hours separate inputs?
They allow the overdue period to be entered precisely without entering more than 23 extra hours.
What happens if the invoice is not yet overdue?
Enter zero overdue days and zero additional hours; the estimated interest is zero.
Why does the calculator use a 365-day year?
It uses a standard 365-day conversion to derive an hourly rate. Another convention may apply in some circumstances.
Accuracy and assumptions
Factors that can affect the estimate.
Does the calculator use simple or compound interest?
It uses simple interest on the outstanding invoice balance.
Are fixed late payment charges included?
No. The calculation excludes fixed compensation, recovery costs, administrative charges, and court costs.
What if the invoice was partly paid?
Calculate interest on the balance that was unpaid for each relevant period, rather than using the original invoice amount for all time.
Can the actual amount differ from this estimate?
Yes. Terms, start dates, applicable rules, balance changes, day-count methods, and rounding can all affect the final amount.
Using the result
How to interpret the outputs carefully.
When does late payment interest start?
The relevant start point depends on payment terms, the due date, the agreement, and applicable requirements.
Can I add VAT to the interest result?
Tax treatment can depend on the transaction and local rules. The calculator does not add or determine taxes.
Is this calculator legal or financial advice?
No. It provides an educational estimate only.
How is hourly late payment interest calculated?
The unpaid balance is multiplied by the annual rate converted to an hourly decimal rate, then multiplied by total overdue hours.
Explore Related Questions
Ready to see what you can calculate?
Open the calculator and get personalized results in seconds.