Pro-rata Salary Calculator
Work out pay for part of a month, from an annual salary.
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Formula
How the calculation works
Pro-rata pay is the annual salary reduced to a day rate and then paid for the days actually worked. At 54,000 a year the month is 4,500, and across a 30-day basis the day is 150, so 11 days pay 1,650. Every step is a division, and each one is a place where two people can disagree.
The disagreement is always about the basis. A 30-day month and a 22-working-day month give different day rates for the same salary: 150 against about 205. Someone joining mid-month at the same salary gets a different first payment depending on which the employer uses, and neither is arithmetically wrong.
That is why the tool asks for the basis instead of assuming one. A calculator that silently picked 30 would be right half the time and would look authoritative while being wrong the other half, which is worse than asking.
Common mistakes
- Using the calendar length of the month as the basis when the employer counts working days, or the reverse.
- Forgetting to reduce the annual salary to a monthly figure first, which gives a day rate twelve times too large.
- Counting weekends as worked days in a month measured by working days, which overstates the payment.
When to use it
- Use it when you join, leave or take a period of leave part-way through a month and want to check the payslip arithmetic.
- It is not the tool for a full month's pay or for an hourly contract; it assumes a salaried post measured in days.
Worked example
At 54,000 a year and a 30-day month, the day rate is 150, so 11 days pay 1,650.
Common questions
How many days should I count in a month?
Use the basis your employer counts in: some use 30 days, some use the working days of that month. The same salary gives different answers under the two, so check first.
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