The calculator uses February 28 as your birthday in non-leap years. This is the convention used by most jurisdictions for legal purposes — driving licences, passport eligibility, and retirement benefits. Some countries use March 1 instead; if your specific situation requires that, add one day to the result on non-leap years.
The calculator uses your device's local date as "today." If you're in UTC+14 and it's already midnight while someone in UTC-12 is still in yesterday, the two of you would get different results for the same birth date. This is correct behaviour — an age calculator should use the local date, not UTC. If you need a result relative to a specific timezone, adjust your device's timezone or enter a custom "as of" date.
Years, months, and days is the way humans normally express age — "34 years, 7 months, 12 days." Total days is the actual count of calendar days since your birth date, counting each day exactly once. Total days doesn't care about months or year lengths — it's a flat integer. They express the same duration in different units. Neither is more "correct"; they're just different representations.
When the birth day-of-month is later than the last day of the current month — for example, born on the 31st and the current month has only 28 days — the calculator counts the end of the shorter month as the monthly anniversary. This prevents the month count from being off-by-one. The remaining days are computed from that adjusted point.
Yes. The tool lets you enter any birth date and any "as of" date. To check how old someone was on a specific date in the past, set the "as of" date to that historical date. To see how old someone will be on a future date, set the "as of" date to the future date.
No. The calculation runs in your browser and no data is sent to a server. The birth date you enter stays in your browser session only. Closing or refreshing the tab clears it.
The tool shows this automatically. The day of the week is calculated from the Gregorian calendar using the Zeller or Tomohiko Sakamoto algorithm — no lookup table. It correctly handles the Gregorian calendar reform date (October 15, 1582) for historical dates, though the practical difference is only relevant for very old historical dates.