Prorated rent calculator
There isn't one way to prorate rent. There are three, and they produce different numbers for the same move-in. This calculator shows all three side by side so you can pick the method your lease actually calls for.
The three proration methods
Enter the monthly rent, choose whether it's a move-in (tenant pays from that date through month-end) or a move-out (tenant pays from the 1st through that date), and pick the date. The calculator runs all three common formulas:
- Banker's 30-day month: rent ÷ 30 × days occupied. Every month is treated as 30 days, so a daily rate is identical year-round. Simple and predictable, but slightly generous or stingy depending on the month's real length.
- Actual days in the month: rent ÷ days in that specific month × days occupied. The most intuitively "fair" method and the one most online calculators silently use. The daily rate changes month to month: February's is the highest, 31-day months the lowest.
- Annualized 365-day: rent × 12 ÷ 365 × days occupied. Produces a single daily rate for the entire year. Common in professional property management and required by some housing programs.
On typical rents the spread between the highest and lowest method runs $50–$200 for the same move-in. That's not rounding error. It's a real number a tenant can dispute if the lease doesn't say which formula applies.
Which method should you use?
The lease controls. If your lease specifies a proration formula, use it, full stop. If the lease is silent, most states have no statutory default, which means whichever method you use should be the one you can defend as reasonable and consistent. The clean fix is to write the formula into the lease itself ("prorated rent is calculated at 1/30th of monthly rent per day") and then show the arithmetic in the move-in record: dates, day count, daily rate, and total. A prorated amount that's documented with its formula almost never gets disputed; a bare dollar amount invites the tenant to run their own math with a different method and call the difference an overcharge.
Caveats
Some jurisdictions and programs (notably certain subsidized-housing contracts) mandate a specific method, so check yours before relying on a default. Move-out proration also interacts with notice rules: if a tenant's notice period runs past their chosen exit date, they may owe rent through the end of the notice period, not the day they hand back keys. When in doubt, prorate per the lease and document the calculation in writing at the time you collect it.