The term prorated means divided or distributed proportionally. It's necessary to prorate amounts that are charged or earned for part of a period. For example, you may start a new job or rent a new apartment part-way through the month. Your employer will need to calculate how much pay is due to you for the time you've worked and how much vacation time you're entitled to, or your landlord will need to work out how much rent you should pay for part of the month.
Write down the amount that would be paid for the full period. For example, your monthly pay before taxes is $2,000, you receive 15 days' vacation a year or you pay $750 a month rent.
Calculate the number of units in a full period. For example, in a full month you would work 20 days, you have to work 12 months a year, and a month's rent covers 30 days.
Divide the amount due for the full period from by the total number of units in the period.
$2,000 salary divided by 20 days = $100 a day. 15 days vacation divided by 12 months = 1.25 days per month worked. $750 rent divided by 30 days = $25 a day.
Multiply your answer by the actual number of units for which the amount is due. For example, you work 15 days in your first month, 11 full months in the first year and you move into your apartment on the 16th of the month:
$100 a day salary x 15 days = $1,500 pay before taxes for that month. 1.25 days vacation x 11 months = 13.75 days vacation in your first year. $25 a day rent x 15 days = $375 rent is due for the first month.