How to Calculate the Age Difference Between Two People

Calculating the age difference between two people is straightforward when both birthdays are known — but the exact figure depends on whether you're counting completed years or the precise number of days.

In Years

Subtract the younger person's birth year from the older person's. But birth year difference alone isn't precise. If Person A was born in March 1985 and Person B in November 1990, they're 5 years apart in birth year — but only 4 years and a few months in actual age for most of the year.

In Days

For the precise gap, convert both birth dates to a day count (days since a reference date) and subtract. Most spreadsheet programs and our Age Calculator can do this instantly. A 5-year gap is about 1,826 days (accounting for leap years).

The 'Half Plus Seven' Social Rule

There's a cultural heuristic sometimes called the 'half-plus-seven' rule: take your age, halve it, add seven — that's the socially acceptable minimum age of a romantic partner. For a 40-year-old: 40 ÷ 2 + 7 = 27. This is informal folk math, not any kind of authority, but it's widely referenced in discussions of age gaps.