Prorated rent calculator

How proration actually works

Prorated rent is the partial month a tenant owes when they move in or out mid-month. The arithmetic is simple — a daily rate multiplied by the days they had the place. What causes arguments is that there are three defensible ways to work out the daily rate, and they produce different numbers.

The three methods

Days in that month. Divide the monthly rent by the actual number of days in the month in question — 28, 29, 30 or 31. This is the most common and the easiest to defend, because the tenant pays for exactly the share of that month they occupied. The quirk is that the daily rate changes month to month: on $1,850 rent, a day in February costs $66.07 and a day in March costs $59.68.

30-day month. Divide by 30 regardless of the calendar. Sometimes called the banker's month. Its appeal is a constant daily rate all year. Its problem is February: a tenant occupying all 28 days of February pays 28/30 of the rent, which means a full month's occupancy for less than a full month's rent. Some landlords cap it so the prorated amount can never exceed the full monthly rent.

Annual, or 365-day. Multiply the rent by twelve, divide by 365, and charge that per day. This gives the truest daily rate across a whole year, and is more often seen in commercial leases than residential ones. Note that it divides by 365 regardless of leap years. It is the least common of the three in residential leases and the most likely to need explaining to a tenant.

Counting the days

Count both the first and the last day of occupancy. A tenant moving in on the 18th of a 31-day month has the unit for the 18th through the 31st, which is 14 days, not 13. The calculator above does this for you, and shows the day count so you can sanity-check it against the lease.

The part that matters more than the arithmetic

Whichever method you use, the lease should say which one. Most disputes about prorated rent are not really about the money — they are about a tenant being handed a number they cannot reproduce. A single sentence in the lease naming the method, plus showing your working on the first invoice, removes almost all of it.

If your lease is silent, state law or local practice may supply a default, and some jurisdictions have their own rules about proration on move-out, particularly where notice periods or rent control are involved. Check before you rely on a default.

Security deposits are not prorated

A common mistake: prorating the deposit along with the rent. The deposit is a fixed sum held against damage and unpaid rent, not a charge for occupancy, so a mid-month move-in does not reduce it. The first month's rent is prorated; the deposit is not.

The other recurring error is prorating both ends of a tenancy using different methods because two different people did the maths a year apart. Pick one, write it in the lease, and apply it to move-in and move-out alike.