Invoice due-date calculator
Choose the invoice date and number of calendar days in the agreed payment term.
Rates checked:
Who should use this calculator
This free calculator is intended for freelancers, sole traders, contractors and small-business owners who need a quick planning figure before preparing or checking an invoice. It can also help clients and bookkeepers understand the arithmetic behind a quoted amount. Use the result as a review aid alongside the relevant agreement, source records and current official guidance, not as an automatic accounting or legal decision.
Calculator methodology
The due date is the invoice date plus the agreed number of calendar days.
This is general information, not tax, legal or accounting advice.
Worked example
An invoice issued on 1 October with an agreed term of 30 calendar days is due on 31 October. A term written as ‘end of month following invoice’ would produce a different date and should not be represented by simply entering 30. Put the actual calculated date on the invoice so the client does not need to interpret it.
Important limitations
This tool adds calendar days only. It does not move dates for weekends, bank holidays or client processing schedules, and it cannot interpret wording such as working days, month-end or payment after acceptance. The signed agreement takes priority. Check that the invoice date is the contractual trigger before relying on the result.
Copy the result into the invoice's due-date field and into your payment-reminder schedule. Keep the accepted quote, contract or client email that states the term. If the parties later agree a new date, record that change rather than silently replacing the original contractual deadline.
Common questions
Does Billoz store my calculator entries?
No. These public calculations run in the browser and are not saved to a Billoz account.
Is the result professional advice?
No. It is an indicative calculation based on the values entered and the displayed method.
Should I keep a record of the calculation?
For an important decision, retain the inputs, result, source and calculation date with the relevant invoice or business record.