Prorated rent and salary calculator (日割り計算)
Result
By days in the month: ¥80,000 × 10 ÷ 31 = ¥25,806
By 30 days: ¥80,000 × 10 ÷ 30 = ¥26,666
10 days, first and last day included. This month has 31 days.
Fractions of a yen are rounded down.
How it is calculated
Prorating divides the monthly amount either by the number of days in that month or by a flat 30, then multiplies by the days used. This page uses no official rates or tables. No law says which divisor to use or how to round fractions of a yen; the contract decides.
For rent, Article 89(2) of the Civil Code (in Japanese) provides that legal fruits (法定果実), meaning income from letting others use property, such as rent, are divided by day according to how long each party holds the right to collect them, for example when a rented building is sold mid-month. It is a default rule and does not say which divisor to use. What you pay for the month you move in or out follows your lease.
For salary, no law sets how to prorate pay for the month you join or leave a job; the employer’s work rules (就業規則), wage rules or your employment contract decide. Some employers instead divide by the scheduled working days in that month, which this page does not calculate.
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FAQ
How is prorated rent calculated in Japan?
Multiply the monthly rent by the days you rent the place, then divide by the days in that month or by 30. For ¥80,000 rent from 22 to 31 October (10 days), that is 80,000 × 10 ÷ 31 = ¥25,806 by days in the month, or 80,000 × 10 ÷ 30 = ¥26,666 by 30 days, rounding down in both cases.
Which is right: dividing by the days in the month or by 30?
Neither is set by law; your contract decides. Dividing by the days in the month makes the daily amount change from month to month, higher in February and lower in 31-day months. Dividing by 30 keeps it the same every month.
How is salary prorated when I join or leave a job?
No law sets the method. It follows your employer's work rules (就業規則), wage rules or your employment contract. Besides dividing by the days in the month or by 30, some employers divide by the scheduled working days in that month.