Age Difference Calculator

How it is calculated

The tool compares two calendar dates and reports the gap as completed years and as total days. Years are whole calendar years that have fully passed from the earlier date to the later one: the year count increases only when the month and day of the later date have reached those of the earlier date. The total is the exact number of days between the two dates, with leap days included. The order does not matter, as entering the older person first or second gives the same answer. Both dates must be valid and filled in; the usual year-month-day format is safest. Because the day count is exact, it is the better figure when you need a precise gap for records, while the years figure is the one people quote in conversation.

Common mistakes

• Subtracting birth years in your head (1995 − 1990). That ignores the month and day: for people born in December 1990 and January 1995 it gives 5, but the real gap is just over 4 years.
• Writing dates in day-month-year order when the field expects year-month-day, which can swap day and month or be rejected.
• Assuming a year is always 365 days when converting the day total. Leap years add days, so dividing by 365 gives a slightly different answer from the whole-year count.
• Expecting the sign to show who is older. The result is always positive; you need to remember which date is earlier.