What is prorated rent?

If a lease starts on the 20th, the tenant usually pays only for the days left in that month, then full rent from the 1st. The same applies at the end of a tenancy that doesn't end on the last day of a month.

The two common methods are a daily rate based on the actual days in that month (monthly rent ÷ days in the month × days occupied) and a daily rate based on a standard year (monthly rent × 12 ÷ 365 × days occupied). They give slightly different results, so pick one and write it into the lease.

Some landlords skip proration by aligning every lease to the 1st, or by collecting the partial month together with the first full month. Whatever you choose, state it in the lease so the first payment holds no surprises.