Two common ways to count days
Actual days in the month divides the rent by the real number of days, so 28, 29, 30 or 31. A 30-day month divides every month by 30, which keeps the daily rate the same all year and is easier to explain. Neither is the only correct answer. What matters is that your lease says which one you use and that you use it every time.
Check your lease and local rules
Some leases start on the first of the month and skip proration altogether. Some places have rules about how partial months must be handled. Use this as a starting figure, then confirm it against your lease and local law.
Keep the numbers with the tenant
In Dr. Landlord you can record a payment by hand with the date, amount and method, so a prorated first month sits in the same history as every other payment. Start free or see the move-in and move-out checklist builder.
General information and an estimate, not legal, tax or financial advice. Nothing you enter here is saved.