Payment terms and late-fee calculator
Work out a due date from your payment terms, and see how much interest and any flat fee come to on an overdue amount. You type every rate and fee.
Nothing is filled in for you. Every date, rate, period and fee comes from you.
Your result
Type an invoice date and payment terms to see the due date.
Type the amount overdue, the due date and the date to calculate to, to see the result.
Saving needs a free account.
What this calculator does
It does arithmetic on the numbers you type: a due date from payment terms, and the interest and flat fee on an overdue amount. It adds no wording about what to charge or whether a charge can be collected. Check your written agreement, and check with the official source or a qualified professional.
How days late and interest are worked out
The due date itself is not a late day. The first late day is the day after the due date plus any days you typed. Interest is simple: the amount overdue × the yearly equivalent of your rate × days late ÷ 365, rounded to the cent once. The flat fee is counted once, when at least one day is late. Example, with made-up numbers for the arithmetic only (not a suggested rate, period or fee): 500.00 with a rate of 1% per month, a due date of 2026-10-01 and 10 days before a charge starts has 0 days late on 2026-10-11 and 1 day late on 2026-10-12, which gives interest of 0.16.
Per month versus per year
A rate typed as per month is multiplied by 12 to get its yearly equivalent, and a rate per week by 52. Example, with made-up numbers: 1% per month is 12% per year, and 1% per week is 52% per year. The page shows the yearly equivalent beside every result so you can see what your rate adds up to over a year. The tool makes no comment on it.
Days before a late charge starts
These days push the first late day later. They apply to the flat fee too: the fee is counted only once at least one day is late after them. With nothing typed, the box counts as 0 and the page shows it.
Due date from payment terms
Type an invoice date and a number of days and the tool counts forward in calendar days. 2026-10-01 plus 30 days is 2026-10-31, which is a Saturday: the tool shows the weekday and does not move the date. Type 0 for due on receipt.
The statement for copying
Copy statement gives you a short paragraph made only from your typed numbers and their results, in a fixed order. It contains no request of anyone. Copying it does not send it. Read it and your written agreement before you send anything.
Printing or keeping a PDF
Print or save as PDF opens your browser's print window. Choose "Save as PDF" as the printer to keep a file. The page is headed Late-fee calculation, and the information notice and the short disclaimer are on it.
Common mistakes
- Counting the due date itself as a late day.
- Mixing up per week and per month when typing the rate.
- Forgetting that the flat fee is counted once, not for every late day.
Using your CSV
Export CSV downloads a two-column file you can open in a spreadsheet: a fixed label and its value for every number above, then the information notice and the short disclaimer. The file has no names or free text. Numbers in the file use a dot.
A note for Canadian businesses
You type the rate and the fee, and this tool does not know or check either. It makes no statement about any rate or fee. Check your written agreement, and check with the official source or a qualified professional.
Questions
Does it tell me what I can charge?
No. It only does arithmetic on the numbers you type and makes no statement about any rate or fee. Check your written agreement, and check with the official source or a qualified professional.
Does it send a reminder?
No. It does not send, schedule or write anything to your client. Copying or printing a result does not send anything to anyone.
Where does the rate come from?
You type it. Canada Business Kit does not supply or check rates, and nothing is filled in for you.
Does it add interest on interest?
No. Interest is simple. It is worked out on the amount overdue only, and not on the flat fee.
What if my agreement states a yearly rate?
Choose year and type that rate. The tool then uses it as it is, with no weekly or monthly conversion.
Does it handle part payments?
Not on its own. If you have received part of the amount, type what is left as the amount overdue.
Do I need an account?
Only to save. Without an account, what you type stays on this page and nothing is saved.