A landlord prorates monthly rent by dividing the total amount of the rent for the month by 30 and multiplying the result by the number of days of the month that the tenant will occupy the property. This calculation allows a landlord to charge a tenant for only part of the month.
Rent is often assessed by the month and made payable on the first day of every month. When a tenant takes possession of a leased property on any day other than the first day of a month, the ordinary expectation is for the tenant to pay only for the days that he actually has control of the property. Prorating the rent calculates the per-day rental cost by dividing the monthly rent by 30 even during the months that technically have 31 days.
Landlords often prorate the second month's rent instead of the first when new tenants move in. This means a full month's rent is due upon move in on any day of the month, while payment for the second month is prorated so that regular rent payments are due on the first day of the month going forward.