ProRata CalculatePro Rata Date Calculator — The Fair Share Between Two Dates
Work out the fair share of an amount for part of a period — a starter’s first month, a leaver’s last month, a refund. Enter the period, your actual dates and the full amount.
Pro Rata Date Calculator
Dates count inclusively: the first and last days both count, matching how rent and payroll usually treat them.
Where date-based pro rata turns up
First and final payslips. Start a monthly-paid job on 13 April and April’s gross pay is the monthly salary scaled by the days you were employed — though as the FAQ notes, payroll may count working days instead, so treat this figure as your cross-check rather than gospel. Rent and licences are priced on calendar days, making this calculator’s default method the right one. Refunds — gym memberships, course fees, insurance premiums, season tickets — are almost always argued in calendar-day shares, and having the fraction (not just a feeling) changes how those phone calls go. Service charges and ground rent on flats change hands between buyer and seller on completion using exactly this arithmetic, usually on the annual-amount method.
Two examples
Leaving a flat early. Your final month’s rent is £1,450 for April (30 days) and you hand the keys back on the 12th, with the landlord’s agreement. Your share is 12 ÷ 30 = 0.4, so £580. If the agent instead charges to the 15th “for cleaning”, that is a negotiation about dates, not arithmetic — settle the end date first, then let the fraction do its work.
A starter’s first month, annual method. You start a £31,000 post on 20 May and want May’s pay to the 31st: 12 days. On the 365-day basis the fraction is 12 ÷ 365 = 0.0329 and the amount is £1,019.18. Payroll using working days (8 working days of 21 in late May) would land near a different figure — both are shown here so you can recognise which one your payslip used.
Questions people ask
It answers “I was only there for part of the period — what share of the full amount is fair?” for anything priced by a period: rent, salaries for starters and leavers, service charges, subscriptions and course fees.
A convention from finance in which every month counts as 30 days, so a year is 360 days. Some payroll and loan systems use it because the arithmetic is tidy. It slightly changes the fraction compared with real calendar days, which is why the calculator offers it as a separate option rather than hiding it.
When the full amount you typed is an annual figure. The 365-day option divides your actual days by 365 directly instead of by the length of the period you entered — right for “I started a £31,000 job on 14 May, what is my pay to 31 May?” style questions where the period that matters is the year.
Because you cannot owe — or be owed — for days outside the period being priced. If your actual end date runs past the period end, only the overlap counts. The result summary tells you when clipping has happened so an unexpected figure never passes silently.
Payroll for salaried starters and leavers often divides by working days in the month, or by 260/261 working days a year. This calculator prices calendar time, which is the correct basis for rent, fees and most charges. For a salaried first or final month, ask payroll which divisor they use — the difference between methods is small but visible, and contracts sometimes name the method.
Rates used: UK tax year 2026/27 · Last reviewed: October 2026. Calculations run in your browser — nothing you type is sent anywhere or stored by us.