Prorated rent calculator
A tenant moving in on the 18th does not owe a full month. This works the partial month three ways, shows the daily rate it used, and prints a line you can staple to the lease so nobody argues about it in November.
Pre-filled with a realistic mid-month move-in. Change any field.
13 of 30 days · September 2026
$801.67
$61.67 per day × 13 days
Which method belongs in your lease
All three are defensible. What is not defensible is choosing whichever is highest after the fact. Name one method in the lease, apply it to move-ins and move-outs alike, and the calculation stops being a negotiation.
| Method | Daily rate on $1,850 | 18 Sep move-in |
|---|---|---|
| Actual days (September, 30) | $61.67 | $801.67 |
| 30-day month | $61.67 | $801.67 |
| 365-day year | $60.82 | $790.68 |
September has 30 days, so the first two methods agree. In a 31-day month they diverge, and February is where a 30-day lease clause quietly overcharges.
What the statute actually governs
Rent-timing statutes say when rent becomes payable, not how to slice a partial month. California's is typical: rent on a monthly holding is payable at the termination of each period, as it successively becomes due. Cal. Civ. Code § 1947 (checked 2026-09-04). Proration is a contract term. If your lease is silent, you are arguing arithmetic with someone who has already moved in.
Put it in the lease
One sentence does it: "Partial months are prorated using the actual number of days in that calendar month." Then the number this page prints is the number the lease already promised.
Move-outs are the other half
Most landlords prorate the move-in and forget the move-out. If a tenant on a month-to-month gives notice mid-month and the notice period ends on the 12th, they owe twelve days, not a month — and the difference belongs on the same statement as the deposit deductions. Read the return deadline before you post it.