Pro Rata Calculator

A pro rata calculator works out the share of an amount that belongs to a partial period. Moving into an $1,800 apartment on the 12th of a 31-day month means you occupy it for 20 days, so you owe 20 ÷ 31 of the rent: $1,161.29 instead of the full month. The same arithmetic prorates a salary, a bill, a refund or a membership fee.

This page covers three jobs in one tool. The rent mode handles a mid-month move-in or move-out and shows all three conventions landlords use. The salary mode handles a partial year and a part-time schedule. The generic mode splits any amount over any period, which is what you want for insurance refunds, HOA dues, subscriptions and shared invoices.

What "pro rata" actually means

Pro rata is Latin for "in proportion". It says nothing about a discount or a negotiation: it simply means that if you used a quarter of the period, you owe a quarter of the amount. Two numbers define every proration. The first is the size of the whole period, measured in whatever unit fits: 31 days in March, 365 days in a year, 40 hours in a full-time week, 12 months in a subscription. The second is how much of that period is yours. Everything else follows from dividing one by the other.

Because the whole period can legitimately be measured in more than one way, two honest people can prorate the same rent and land on different numbers. That is not an error in the math, it is a difference in the convention, and it is why a lease or an offer letter should state which convention applies.

The pro rata formula

Every mode of this calculator uses one formula:

It is often easier to do it in two steps. First find the rate per unit, then multiply by the units you used:

For a move-in, the days occupied include the move-in day itself, so the count is Days in month − Move-in day + 1. For a move-out, you are charged from the 1st through the move-out day, so the count is simply the day number. Getting that "+ 1" right is worth exactly one day of rent.

Worked example: prorated rent for a mid-month move-in

Rent is $1,800 a month. You take possession on March 12 and the lease prorates the first month using the actual days in the month.

• Days in March: 31.
• Days occupied: 31 − 12 + 1 = 20 days, which is 64.52% of the month.
• Daily rate: $1,800 ÷ 31 = $58.06 per day.
• Prorated rent: 20 × $58.06 = $1,161.29.
• Compared with a full month: you pay $638.71 less for March, then $1,800 from April onward.

Move the same date into a 30-day month and the answer changes: April 12 gives 30 − 12 + 1 = 19 days at $60.00 a day, or $1,140.00. Move it into February and 28 − 12 + 1 = 17 days apply. The day count, not the date, drives the number.

The three ways landlords prorate rent

American leases use three conventions, and none of them is universally "correct". The table below prices 20 days of occupancy in a 31-day month under each one.

The actual-days method is the most intuitive and the cheapest for the tenant in a long month. The 30-day method, sometimes called the banker's month, gives every month the same daily rate, which is simple for accounting but charges slightly more per day in a 31-day month. The 365-day method converts rent to an annual figure first, then divides by 365, which sits between the two and is common in corporate and multi-unit property management. On a $1,800 rent the whole argument is worth about $39, but on a $3,000 unit it is $64.52.

Prorated rent by move-in day

The next table applies the actual-days method to $1,800 monthly rent for common move-in days in a 28-day February, a 30-day April and a 31-day March. Read the day count first, then the amount.

Notice that a mid-month move-in never costs exactly half. Because the move-in day counts, taking keys on the 15th of a 31-day month buys 17 days, or 54.8% of the month, not 50%. The shorter the month, the more each single day is worth: one day of February rent is $64.29, while one day of March rent is $58.06.

Worked example: pro rata salary for a partial year

You accept a role paying $78,000 a year and start on September 14. Your employer prorates by calendar days over a 365-day year, and the year ends December 31.

• Days worked: September 14 through December 31 is 109 days, or 29.9% of the year.
• Daily rate: $78,000 ÷ 365 = $213.70 per calendar day.
• Pro rata salary for the year: 109 × $213.70 = $23,293.15.

If the employer prorates by work days instead, the arithmetic changes. There are 261 weekdays in 2026 and 79 of them fall between September 14 and December 31, so the daily rate becomes $78,000 ÷ 261 = $298.85 and the pro rata pay is $23,609.20 - about $316 more than the calendar-day method. A third employer might skip days altogether and pay whole semi-monthly checks of $78,000 ÷ 24 = $3,250 for each period you were on payroll. Ask which basis your payroll uses before you compare an offer against your current pay.

Part-time pro rata salary by hours

A job advertised at "$80,000 pro rata" for a part-time schedule does not pay $80,000. It pays the full-time figure multiplied by your share of a full-time week. The table applies that fraction against three common full-time salaries, using a 40-hour standard week.

Watch the standard week. If the employer treats 37.5 hours as full time, working 30 hours is 80% rather than 75%, and a $80,000 role pays $64,000 instead of $60,000. Change the full-time hours field in the calculator to match the handbook, not the assumption.

Prorating bills, dues and refunds

The generic mode covers everything that is not rent or salary. Cancel a $1,440 annual policy after 100 days and you have used 100 ÷ 365 of it, or $394.52; the unused 265 days are worth $1,045.48. HOA dues for a home sold mid-quarter, an annual software licence split between two departments, a utility bill divided among roommates by days present, a membership that starts mid-cycle: all use the same two numbers, units used and units in the full period.

The unit does not have to be a day. Prorating a shared server bill by gigabytes, a shipping invoice by pallets, or a bonus pool by headcount is the same formula with a different label. Set the unit name in the calculator so the output reads the way you need it for an invoice.

How to use this calculator

1. Pick a mode: rent for a partial month, salary for a partial year or a part-time schedule, or any amount for everything else.
2. Enter the full amount: the monthly rent, the full-time annual salary, or the price of the complete period. Always use the undiscounted figure.
3. Set the period: in rent mode choose the month, day and year, and say whether it is a move-in or a move-out. The day count updates automatically, including February in leap years.
4. Choose the convention: actual days, a 30-day month or a 365-day year. The comparison table underneath shows all three so you can see what is at stake.
5. Read the result: the headline is the amount due, and the tiles show the rate per day or unit, the days charged, and how much less than a full period you are paying.

Who this calculator is for

Tenants and landlords settling a first or last month. Property managers issuing move-in statements. New hires and HR checking a first or final paycheck, or turning a "pro rata" job ad into a real number. Part-time employees comparing a reduced schedule against a full-time salary. Freelancers and small businesses invoicing a partial retainer month. Homeowners splitting HOA dues or an insurance refund at closing. Roommates dividing rent when one person arrives or leaves mid-month.

Key terms

• Pro rata: in proportion. The share of an amount that matches the share of the period.
• Proration: the act of splitting the amount. "Prorated" is the American verb form of the same idea.
• Daily rate: the full amount divided by the number of days in the period. The building block of every rent proration.
• Banker's month: a 30-day month used regardless of the calendar, so every day has the same value all year.
• FTE (full-time equivalent): your hours divided by full-time hours. 20 of 40 hours is 0.5 FTE.
• Pay period basis: the number of paychecks in a year - 12 monthly, 24 semi-monthly, 26 biweekly, 52 weekly. Proration can be done in whole pay periods instead of days.
• Prorated refund: the unused portion of an amount already paid, returned when a term ends early.
• Terminal period: the final partial pay period or rental month, prorated the same way as the first one.

What changes the result

• The month you move in. A day of a 28-day February is worth 11% more than a day of a 31-day month at the same rent.
• Whether the first day counts. Including or excluding the move-in day shifts the bill by one full day, every time.
• The convention in the lease. Actual days, 30 days or 365 days can differ by $25 to $65 on a single month.
• Calendar days versus work days for salary. The same start date can produce a few hundred dollars of difference on a mid-size salary.
• The definition of a full-time week. 35, 37.5 and 40 hours all appear in American handbooks, and each one changes the part-time fraction.
• Leap years. February 29 adds a day to the month and to the year, lowering every daily rate slightly.
• Items that are never prorated. Security deposits, application fees and most flat administrative charges are due in full whatever the date.

Tips for getting proration right

• Get the method in writing. A lease or offer letter that says "prorated on actual days, move-in day included" removes every future argument.
• Do the arithmetic before you sign, not after the invoice arrives. A move-in date two days earlier can cost more than it saves in overlap.
• Round to the cent, not to the dollar, and round only at the end. Rounding the daily rate first can shift the total by a dollar or more.
• Keep the full-month figure visible. Property managers post the full rent and a separate credit as often as they post one prorated number.
• For a final paycheck, check whether accrued paid leave is paid out and whether it is prorated too. That is set by state law and company policy, not by this formula.
• When you prorate a bill among people rather than over time, make sure the shares add up to exactly 100% before anyone pays.

Limitations

This calculator does the proportional math and nothing else. It does not apply payroll taxes or withholding, so a prorated salary here is gross pay. It does not know your state or city rules: some jurisdictions regulate move-in charges, notice periods and final-paycheck timing, and a few leases override the calendar entirely by charging a full month regardless of the date. It does not handle salaried exempt employees whose pay may be protected from partial-week deductions under federal rules except in defined situations such as the first and last week of employment. And it assumes the full amount is the correct starting point - if your rent includes a concession, a utility allowance or a scheduled increase, prorate the amount that actually applies to those days.

Which calculator to use next

Use this page when you need a share of a period. Use the Salary Calculator when you want a full-year salary converted between hourly, weekly, monthly and annual, and the Hourly to Salary Calculator or the Salary to Hourly Calculator when the question is a rate conversion rather than a partial period. Reach for the Paycheck Calculator once you want the take-home figure after tax, and the Pay Raise Calculator when a new salary starts mid-year and you want the new annual number before prorating it here.

• To count the exact days between two dates before prorating, use the Date Calculator, or the Business Days Calculator for a work-day basis.
• To turn a share into a percentage or back again, use the Percentage Calculator.
• To check how much rent fits your income before you sign, use the Rent Affordability Calculator.
• To total hours before prorating a wage, use the Timesheet Calculator or the Time Clock Calculator.
• For hours past 40 in a week, which are paid at a premium rather than prorated, use the Overtime Calculator.