Calendar borrowing is ancient
“Borrowing” days from the previous month mirrors techniques in Babylonian and Roman calendars, where month lengths shifted to stay in sync with seasons.
History
Age Difference Calculator — Years, Months, & Days Between Birthdays
Age Difference
Older/younger is detected automatically.
Calculated at midnight UTC to avoid daylight-saving surprises.
About This Age Difference Calculator
Want a quick, reliable way to see the gap between two birthdays? This age difference calculator turns any two dates into a clear breakdown of the age gap in years, months, and days, along with practical totals like overall days or weeks. It is designed for everyday use, whether you are comparing birthdays for fun, planning milestones, or checking eligibility ranges, and it presents the result in a format people can understand at a glance.
Behind the scenes, the calculator performs a simple calendar subtraction: it finds the earlier date and the later date, then measures the distance between them in real calendar units. Months do not all have the same length, and leap years add an extra day, so the tool accounts for those differences instead of assuming every month or year is identical. If the day portion of a subtraction would go negative, the calculator “borrows” days from the previous month of the later date, then adjusts the months and years accordingly. This approach mirrors how people count ages in real life and ensures the result matches actual calendar rules, including Feb 29 birthdays.
Using the calculator is straightforward. First, enter Birthday A and Birthday B. You can pick any dates, past or future. Then click Calculate to see who is older, how many full years and months separate the dates, and the exact days difference. If you entered the dates in the wrong order, the Swap button flips them instantly. Use Clear to start over, or Copy Result if you want to paste the age gap into an email or note.
Common examples include comparing siblings’ birthdays, estimating school grade spacing, planning anniversaries, or checking age requirements for activities, jobs, or benefits. It is also handy for relationship age gap discussions, adoption or guardianship paperwork, and general date difference questions when you want a precise, calendar-aware answer. Everything runs locally in your browser for speed and privacy, so no personal data is sent anywhere.
Age Difference: FAQs
How do you get years, months, and days exactly?
We subtract the earlier birthday from the later one. If the day would be negative, we “borrow” the number of days from the previous month of the later date, then adjust months/years. This respects actual month lengths and leap years.
Do I need to pick times?
No. This tool works with dates only; time-of-day is ignored. All math runs at midnight UTC for stability across regions.
What about Feb 29?
It’s handled naturally by real calendar lengths. If one birthday is Feb 29 and the other is in a non-leap year, the borrow step still uses the correct month length.
Is my data private?
Yes. All calculations are local in your browser. Nothing is uploaded or stored.
5 Fun Facts about Age Gaps
Leaplings distort averages
A Feb 29 birthday makes your age gap “tick” every four years; over time it nudges average days-between, especially in long spans.
Leap quirks
Biggest recorded sibling gap
Families with children 25+ years apart exist—meaning a sibling could already have a graduate degree before the youngest is born.
Real-world gap
“Decimal years” aren’t linear
Converting an age gap to decimal years uses 365.2425 days per year (Gregorian average), so 6 months isn’t exactly 0.5 when spanning a leap year.
Math twist
Age gaps and milestones
A 5-year gap means you’ve celebrated about 1,826 more sunrises than someone five years younger—helpful perspective for “who’s older” debates.
Perspective