The formula, and how to count the days
Move-in: count from your move-in day to the last day of the month, inclusive — (last day − move-in day + 1). Move-out: count from the 1st to your move-out day. Both endpoints are days you are charged for.
Divide by the actual days, not a flat 30
The daily rate changes with the length of the month. Splitting the same $1,200 rent by the real day count instead of a flat 30 shifts the daily rate by a few dollars — in your favor in long months, against you in February.
Same $1,200 rent, three daily rates. The flat ÷30 method overcharges in a 31-day month and undercharges in February — up to about $2.86 a day either way.
Daily rate on $1,200 rent, by month length
| Days in month | Daily rate | 14 days | vs flat ÷30 |
|---|---|---|---|
| 28 (Feb) | $42.86 | $600.00 | +$40.00 |
| 29 (Feb, leap) | $41.38 | $579.31 | +$19.31 |
| 30 | $40.00 | $560.00 | $0.00 |
| 31 | $38.71 | $541.94 | −$18.06 |
Scale the daily rate for your own rent: divide your monthly rent by these day counts. Utilities, parking and pet fees are usually flat and are not prorated unless the lease says so.
Where people slip up
- Forgetting the +1. Moving in on the 15th of a 31-day month is 17 days occupied (15th through 31st), not 16.
- Ignoring February. A short month has a higher daily rate, so the same partial stay costs more per day.
- Tenant swaps. If one tenant leaves the 15th and another arrives the 16th, prorate each separately rather than splitting the month in half.
Common questions
How do I calculate rent for a partial month?
Divide the monthly rent by the number of days in that month to get a daily rate, then multiply by the days you actually live there. For $1,200 rent, moving in on the 17th of a 30-day month: 1,200 divided by 30 is $40 a day, times 14 days is $560.
Do I count both the move-in and move-out day?
Yes. If you move in on the 15th and the month ends on the 30th, that is 16 days, not 15. Count the day of the month minus the move-in day, then add one for the first day.
Should rent be divided by 30 or by the actual days in the month?
Actual days is the fairer method and the one HUD requires. A flat 30-day divisor overcharges you in a 31-day month and undercharges in February. Check your lease, since some contracts specify one or the other.
