Free Invoice Generator

Pro-rata calculator

A retainer that starts on the 17th, a contract that ends mid-month: this works out the share of the fee for the days you are billing, in calendar days or working days, and shows how far apart the two come out.

The fee

What you would charge for the whole month or period.

Used only if you press Create this invoice, at the start of the line it becomes.

The period

Your contract decides which. Public holidays are not taken out: they depend on the country.

The days you are billing

Both this day and the last one are counted.

Leave it empty to bill to the end of the month.

GuideHow retainers workHow this works, and where the figures go wrong →

What the pro-rata calculator does not do

  • It does not take out public holidays, even when counting working days. They depend on the country and the region, and skipping the wrong ones would be worse than skipping none.
  • It does not use a 30-day month. Some contracts divide every month by 30 whatever its length; this page counts the days each month has, so under such a contract its figure for a 28- or 31-day month will differ from yours.
  • It does not span months. A stretch from one month into the next is two part-months, each billed against its own length, and this works out one at a time.
  • It does not keep anything. Nothing is written to your browser's storage while you use it and nothing is sent to us, so the figures are gone when you close the tab. Press Create this invoice if you need a document: the figures are handed to the invoice generator in this tab, cleared as soon as it opens, and saved there as a new invoice alongside any you already have.

Related

To see what a monthly retainer pays per hour once the month is worked, use the retainer calculator. For the working days between any two dates, see the business days calculator. To split a project price into payments rather than a fee into days, use the payment schedule calculator.

Last updated 24 September 2026