The three proration methods
Days in the month: divide the monthly rent by the number of days in that specific month (28, 29, 30 or 31) and multiply by the days occupied. It is the most common method and the easiest for a tenant to check, but the daily rate changes from month to month.
Days in the year: multiply the monthly rent by 12, divide by 365 (366 in a leap year) and multiply by the days occupied. The daily rate is the same all year. A 30-day month: divide the rent by 30 regardless of the month, which keeps the arithmetic simple but charges slightly more for a short stay in a 31-day month. Days are capped at 30, so nobody pays more than one month's rent.
A worked example
A tenant signs for $1,500 a month and moves in on 20 October. Counting the move-in day, they occupy the unit for 12 days of a 31-day month. By days in the month the daily rate is $1,500 ÷ 31 = $48.39, so the prorated rent is $580.65.
By days in the year the daily rate is $18,000 ÷ 365 = $49.32, giving $591.78. With a 30-day month it is $50.00 a day and $600.00 for the 12 days. Same tenant, same dates: a spread of almost $20, which is why the method belongs in the lease rather than being decided when the first invoice goes out.
Move-in versus move-out
For a move-in, the calculator charges from the move-in day through the last day of the month, inclusive. For a move-out, it charges from the 1st through the move-out day, inclusive. Whether the move-in or move-out day itself counts is a convention, not a law of nature; most leases count the day the tenant gets the keys and the day they hand them back.
Move-out proration is less automatic than move-in proration. Many leases and state statutes require a full notice period, so a tenant who leaves on the 10th may still owe rent until the notice runs out. Check the lease and your state's rules before refunding part of a month, and record what was agreed on the move-in / move-out checklist.
Prorate the first month or the second?
Some landlords collect a full first month at signing and put the prorated amount on the second month's invoice. That simplifies the first payment and makes sure a full month is in hand before the keys change hands. Others collect the prorated amount up front so that every later invoice is a clean full month. Either works, as long as the lease says which and the tenant gets a receipt for each payment; the free rent receipt template covers partial-month payments.
If you collect rent online, set the first charge to the prorated amount rather than editing it by hand later. How to collect rent online walks through setting up recurring charges, and the security deposit is a separate figure that should never be prorated; security deposit management covers holding and returning it.
Writing proration into the lease
One sentence is enough: name the method, say whether the move-in day counts, and say when the prorated amount is due. For example, "Rent for a partial month is calculated by dividing the monthly rent by the number of days in that month and is due on the move-in date." Clear wording prevents most disputes, because the tenant can repeat the calculation themselves.
Common questions
How do you calculate prorated rent?
Divide the monthly rent by the days in the month (or the annual rent by the days in the year, or the monthly rent by 30) to get a daily rate, then multiply it by the number of days the tenant occupies the unit in that month.
What does prorated rent mean?
It means the tenant pays only for the part of the month they live in the unit, instead of a full month's rent, usually in the month they move in or move out.
Is a landlord required to prorate rent?
Usually not for a move-in; it is a matter of what the lease says. Move-outs depend on the notice period and state law, which often require rent until the notice period ends. Check the rules for your state.
Does the move-in day count as a day of rent?
In most leases, yes: the tenant has the keys that day. The calculator counts both the move-in day and the move-out day. If your lease says otherwise, subtract one day.
Which proration method is fairest?
Days in the month matches what the tenant actually occupies. Days in the year gives a steady daily rate. A 30-day month is simplest. All three are acceptable if the lease names one and you apply it consistently.
Done by hand once. Done automatically from now on.
Set the first charge to the prorated amount and let every later month invoice itself.