How to use the mid-period salary proration calculator
- Enter the pay for the full period, and the dates the pay period starts and ends.
- Enter the first and last day worked. Both are counted as days worked.
- Choose whether working days are Monday to Friday or Monday to Saturday. In the advanced option, list days off for everyone, such as company holidays.
- Read the prorated pay by three methods, with the days used, the share of the period and the pay per day.
Formula
calendar days: days worked / days in the period
working days: working days worked / working days in the period (weekends and listed days off left out)
30-day months: days worked / days in the period, counting every month as 30 days and the last day of a month as the 30th
prorated pay = full-period pay x share, rounded to the cent (half up)
All three use whole days, with the first and last day included.
Starting on November 12
Monthly pay of $5,000 for November 1 to November 30, with work from November 12 to November 30 and November 26 off for everyone. By calendar days, 19 of 30 days is 63.333 percent, or $3,166.67. By working days, 12 of 20 is 60 percent, or $3,000.00, since November 2026 has 21 weekdays and one is a day off. By 30-day months it is 19 of 30 again, $3,166.67.
In February 2027 (28 days), starting on the 15th gives 14 of 28 days, which is $2,500.00 by calendar days, and 16 of 30 on a 30-day calendar because the 28th counts as the 30th, which is $2,666.67, a gap of $166.67.
Why the methods differ
Calendar days treat every day alike, so a worker who starts just before a weekend gets paid for it. Working days follow the workweek, so they pay more for periods with fewer working days and less for periods with more. The 30-day method is common for monthly salaries and makes a month always the same size, so a mid-February start is paid more per day than a mid-March one. None is right for everyone.
Employers choose the method and write it into their pay policy or offer letter, and some rules may fix the method or the rounding. Ask which one applies to you. For rent, use the proration calculator. For hourly pay see the gross pay calculator, and for changes in pay see the pay raise calculator.
Not payroll advice
This page shows three common ways so you can see how far apart they land. It is not payroll or legal advice, and it does not handle taxes, benefits or unpaid leave. The date-based tools in the same family include the corrected age calculator for another kind of date arithmetic.
Assumptions and limits
- The period is at most 366 days, and the first and last days worked are inside it.
- The full-period pay is the same however many days the period has.
- Days off are dates written like 2026-11-26. They are left out of the working-day counts, not out of calendar days.
- Amounts are rounded to the cent, half up, after multiplying by the share.
Frequently asked questions
Does the 30-day method treat the 31st like the 30th?
Yes. The last day of any month counts as the 30th, and a 31st that is not the last day of a month does not exist. So January 30 and January 31 are both counted as day 30.
Why does a holiday change the working-day share?
A day off for everyone is removed from both the days worked and the days in the period, so the rest of the days carry more weight.
Which method should I use?
Use the one your employer states. If none is stated, the calendar-day method is the simplest to explain, and the others are alternatives to compare.
Can I prorate for the last day instead of the first?
Yes. Leave the first day worked at the period start and set the last day worked to the day the work ends.