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
Enter two birthdays to get the exact difference in years, months, and days, plus helpful totals like days and weeks. The algorithm handles leap years, end-of-month borrowing, and Feb 29 birthdays. Results are deterministic because we compute at midnight UTC and use actual month lengths for the calendar math.
Typical use cases include relationship age gaps, sibling age spacing, compliance or eligibility checks, and general curiosity. No data leaves your device—everything is computed locally for speed and privacy.
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