Java YearMonth.atEndOfMonth: calculate a month boundary without guessed days

Compute the boundary from the calendar

A billing period ending in February does not have a constant day count. YearMonth carries the year and month without inventing a day; atEndOfMonth resolves the final date. The fixture prints February in a leap year and a non-leap year.

For a half-open timestamp range, use the first day of the next month as the exclusive end, then resolve that local boundary in the customer's zone. Exclusive date ranges avoid a fabricated last instant with guessed precision.

Keep policy separate from representation

A calendar month is not thirty elapsed days. If a contract renews on the last day, recompute from YearMonth each cycle. Repeated plusMonths can drift after a short month.

Working program

import java.time.YearMonth;

public class InvoiceMonthBoundary {
    public static void main(String[] args) {
        System.out.println(YearMonth.of(2024, 2).atEndOfMonth());
        System.out.println(YearMonth.of(2025, 2).atEndOfMonth());
        System.out.println(YearMonth.of(2024, 2).plusMonths(1).atDay(1));
    }
}

Output

2024-02-29
2025-02-28
2024-03-01

Cost and ownership

YearMonth and LocalDate are immutable fixed-size values. The operation is constant application work and storage; the larger risk is using a guessed day count and billing a different range from the one stated to users.

Common Mistakes

• Do not hard-code February 28 as its last day.
• Do not model a calendar month as a fixed Duration.
• Do not append 23:59:59 as a substitute for an exclusive upper bound.

Read next

localdate exclusive range, period month end arithmetic, Java Duration versus Period across a daylight-saving change, Java date and time: local schedules versus instants.