Age Calculator Sri Lanka — Exact Years, Months, Days

The calculator uses the standard calendar-borrowingrule — the same one date-fns' differenceInCalendarMonths family of helpers implements, and the same one mainstream age sites (calculator.net, timeanddate.com) use. It produces an answer that always reconciles: adding the years, months, and days back to your birth date returns the reference date to the day.

Given a birth date B and a reference date R:

1. Compute raw differences for each field: ΔY = R.year − B.year, ΔM = R.month − B.month, ΔD = R.day − B.day, and the same for hours, minutes, seconds.
2. If seconds < 0, borrow 60 seconds from minutes. If minutes < 0, borrow 60 from hours. If hours < 0, borrow 24 from days.
3. If days < 0, borrow the number of days in the calendar month immediately before the reference month — that's real month-aware borrowing, not a 30-day approximation. So if R is in March, you borrow 28 or 29 (Feb), not 30.
4. If months < 0, borrow 12 from years.

The total counters (months, weeks, days, hours, minutes, seconds) are computed independently from the raw millisecond difference R.time − B.time, divided by the right constant. Total months is years × 12 + months from the calendar breakdown — using whole calendar months, not 30-day buckets.

For leap-day birthdays (Feb 29), the next-birthday section uses the common-law convention of rolling to Feb 28 in non-leap years — which is also the practice followed by the Sri Lanka Registrar General's Department when issuing age-dependent documents. The Gregorian leap-year rule applied is the full one: divisible by 4, except centuries unless divisible by 400.

To guard against single-algorithm bugs, the years figure is cross-checked against an independent year-only algorithm that compares (month, day, time) tuples directly. The two algorithms must agree before the "cross-checked" badge appears in the calculator header.

In Sri Lanka several key rights, licences, and services are tied to exact age thresholds. Use the calculator above to verify whether you (or a family member) have reached these milestones, or to find out exactly how many months remain until you do.

Passport validity: adult passports (age 16+) are valid for 10 years; passports for persons under 16 are valid for 5 years. Sri Lanka passport photos must show the applicant with a neutral expression against a white background (size: 35 × 45 mm).

• ECMA-262 — JavaScript Date object specification
• Gregorian calendar — leap year rules (Wikipedia)
• ISO 8601 — duration format (PnYnMnDTnHnMnS)
• date-fns — differenceInCalendar* reference implementation

Algorithm and worked examples last cross-checked on 2026-05-11. The Gregorian leap-year and calendar-borrowing logic don't change, so this page is reviewed annually rather than on a fixed schedule.