Late Payment Interest & Statement
Most small businesses chasing an unpaid invoice ask for the invoice total, because working out anything more is fiddly — and that leaves money on the table and makes a weaker ask. Paste your unpaid invoices, one per line, enter the annual rate you are entitled to charge and the date you want interest calculated to, and this produces a statement of account: days overdue counted in real calendar days for each invoice, simple daily interest on the balance that was actually outstanding on each of those days, any fixed compensation you are claiming, and the total — plus the amount the debt grows by every further day, which is the figure that gets an invoice paid this week rather than next month. Part-payments are handled properly: the accrual changes on the day the money arrived, not at the start or the end of the period. Every sum is done in whole minor units of your own currency, so the statement foots exactly. No rate, no compensation amount and no payment term is built in — those come from your contract or from the rules where you are, and you enter them. This is not legal advice, and computing interest is not the same as being entitled to charge it.
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Inputs
- Calculate interest up to (as-at date)
2026-01-31 - Annual interest rate % you are entitled to charge
0 - Fixed compensation per late invoice (0 if none)
0 - Default payment terms in days (0 = each line states its due date)
0
Frequently asked
What interest rate should I put in?
The one you are actually entitled to charge — which comes from your own contract if it sets a rate for late payment, and otherwise from whatever the rules of your own jurisdiction provide when a contract is silent. This tool deliberately has no rate built into it: rates are set by contract or by local rules, both change, and a stored number would be confidently wrong for most people who used it. Check your contract first, then your jurisdiction's rules, then type the figure in.
What day-count convention does it use?
Actual days over a fixed 365-day year, simple interest, not compounded. Daily interest is the balance outstanding that day multiplied by your annual rate and divided by 365. That is stated on every statement it produces, because conventions genuinely differ — 360-day years and true-year counts are both used — and an unstated convention is a hidden assumption. If your contract specifies a different basis, the day counts here are still exact and you can rebase the interest from them.
Why do I have to type in the date?
Because this tool has no clock. It runs entirely on your device, offline, and never reads the time. A figure that may end up in a statement or a claim should not rest on a date something else guessed at, so you enter the date you want interest calculated to and that date is printed on the result.
How are part-payments handled?
On the day they arrived. Interest accrues on the full balance from the due date until the payment date, and on the reduced balance from the payment date onwards. A quick calculation usually applies the payment at the start of the period (understating what you are owed) or at the end (overstating it); both give a different answer. You can enter as many part-payments per invoice as you need.
Will the numbers add up exactly?
Yes. Every amount is held in whole minor units — cents, pence, øre, whatever you invoice in — and never as a floating-point number. Each invoice's balance-days are totalled as exact integers and rounded once, and the statement total is the sum of those rounded per-invoice figures, so the column adds up exactly as printed.
What is the 'fixed compensation' field?
Some contracts, and some jurisdictions' rules, allow a fixed sum per late invoice on top of interest. If yours does, enter that amount and it is counted once for each invoice that went unpaid past its due date. If you leave it at zero, nothing is claimed. No amount is built in, for the same reason no rate is.
Does this mean the debtor has to pay?
No, and this tool never says so. It is arithmetic: it tells you what the interest comes to on the figures and the rate you entered. Whether you are entitled to charge that interest, and what you can do about it, depends on your contract and on the law where you are. This is not legal advice.
Can it write the demand letter for me?
Not this tool — this one produces the numbers. The premium Freelance & Small Business pack includes a Late Payment Demand letter designed to take exactly these figures: the per-invoice principal, the interest, the compensation, the total, and the daily accrual figure. Work the numbers out here first, then put them into that.
What happens to an invoice that is not overdue yet?
It appears on the statement with its principal and zero interest, marked NOT YET DUE at your as-at date. It is included in the principal total, so the statement still shows the whole account, but it never accrues interest and never carries compensation.
What if a line has a bad date?
It is reported, not silently fixed. A date that does not exist (29 February in a non-leap year, or 30 February in any year), a due date before its invoice date, or a part-payment dated before the invoice or after your as-at date all put the line into a 'lines not included' list with the reason. Nothing is quietly normalised into a different date.