Comparing calendar dates accurately

Use a date calculator for days between events, but first decide whether the start day, end day, or both should be counted. That convention changes deadline and duration answers.

Write dates with month names when sharing across regions and use a named time zone when a deadline includes an hour. Leap days and month ends deserve a double-check. Preserve the original dates beside the calculated gap so another person can verify it.

Are you counting elapsed days or inclusive calendar days?