Read the ledger.
Map customer, stable customer/account ID when available, invoice reference, due date, original total, outstanding balance and currency. Broken or ambiguous rows are stopped immediately.
Late-payment interest calculator for UK businesses
Know what is actually owed.
Upload your invoice export. Invoice Owed works out the statutory interest and fixed sum each overdue invoice carries under the Late Payment Act, separates the invoices that clearly qualify from the ones that need a second look, and gives you reminder letters to send yourself.
Fail-closed by design · GBP only in this release · no guessed facts
Late-payment schedule / September
Qualified statutory sums
Statutory interest and fixed sums£2,814.4312 qualified invoices · 4 blocked for review
Northstar Studio Ltd£780.42Ready
Parkfield Joinery£1,140.00Ready
Harbour & Co—Review
No silent currency conversionAmbiguous $ and number formats block.
No guessed datesAmbiguous numeric dates require confirmation.
No inherited answersEach import is qualified again.
No false certaintyUnresolved facts stay outside totals and letters.
Workflow
Three passes. No black box.
The product behaves more like a pre-flight checklist than a plain calculator. It first validates the accounting data, then confirms the Act applies, then produces the schedule and the letters.
Check the Act applies.
Confirm who the customer is, that the invoice is a UK business-to-business sale of goods or services, how the invoice was structured, and what your contract says about late payment.
See what you are owed.
Resolve any payment or credit history and duplicate rows, then read the exact outstanding principal, statutory interest and fixed sum per invoice before downloading a reminder letter.
Release philosophy
Unknown means blocked.
Interest on your own invoices is a bad place for optimistic defaults. These gates are intentionally strict so the software never turns missing data into a confident figure.
Money integrity
Currency signals, decimal separators, original totals and outstanding balances must reconcile before a row is claimable.
FAIL CLOSEDPayment history
Partly paid invoices without a payment history are shown as a marked minimum, with interest and the fixed sum both taken from the current balance; they become exact once the dated reductions reconcile. Fully paid invoices need payment history or an explicit single-payment confirmation.
FAIL-CLOSEDDoes the Act apply?
The statutory rate is applied only after you confirm the sale was UK business-to-business, the invoice is an ordinary invoice for delivered goods or services, and no exclusion applies.
IMPORT-SPECIFICSole-trader customers
A final notice to a sole trader in England and Wales needs extra facts about the agreement and a 30-day reply window, so those notices stay locked until you have entered them.
30-DAY NOTICEPricing
One price. First letter free.
Import, qualify and see the full statutory schedule at no cost. Your first customer letter is free as well. Subscribe when you are ready to write to every customer on the ledger.
See what is owed
CSV import, fail-closed checks, exact interest and fixed sums for every qualifying invoice, and the reminder letters for one customer.
Start free →Letters for every customer
Unlimited reminder letters and final notices for every customer on your ledger. Cancel any time; access runs to the end of the paid period.
Full pricing details →VAT is added at checkout where applicable. Payments are handled by Paddle, our merchant of record.Turn the export you already have into a clear late-payment schedule.
Xero, QuickBooks, FreshBooks, Sage or a normal CSV.