Method, sources and limits

Every figure on this site is produced by a tested module from a named source, and every one of them stops being reliable somewhere. This page says where. None of the figures on it are typed by hand — the ranges, counts and descriptions below are read out of the same code that produces the tables, so this page cannot drift out of date while the site changes underneath it.

What this site is

Age Reckoner answers how old someone is in the systems that disagree about it: the Gregorian calendar, the Hijri calendar, the East Asian traditional counts, the Hebrew calendar, the Solar Hijri calendar, and the orbital periods of the planets. It is two things sharing one set of calculations — 9 explainer pages written for a person, and 7 reference tables written for anything that reads.

The reference tables are the part worth citing. "You are 8,231 days old" is true for one person for one second. "Lunar New Year fell on 10 February 2024" is a fact that stays put, and this site publishes 199 years of them, 60 stem-branch combinations, 5 imperial eras to the day, and the month names of four calendars in their own scripts.

Who makes this

Age Reckoner is written and maintained by Eser Sekercioglu. It is an independent project: no company stands behind it, it carries no advertising, and it sells nothing. The calculations, the tables and the prose on every page are the author's responsibility, and corrections go straight to the author at the address at the foot of this page. Other work by the same author is on GitHub.

Where each answer comes from

Where each one stops

Two limits are worth repeating outside a table, because they affect more people than the range checks do. A Hijri day and a Hebrew day both begin at sunset, not at midnight, and this site works in civil days: if a birth was after dark, the date shown for those two calendars is the day before the one most observance would use. And Japanese era years are published only from 1 January 1873, when Japan adopted the Gregorian calendar; before that the official calendar was lunisolar and a Gregorian date does not map onto an era year without saying which conversion produced it.

How the numbers are kept honest

One implementation, never two. The tables on the reference pages and the answers in the calculator come from the same functions — a table cannot say one thing while a calculation says another, because there is only one of each. Every one of those functions is a pure function of its inputs with no clock inside it, which is what makes them testable at all.

The build refuses to publish a site that fails its checks. It type-checks, runs the test suite over the calendar modules, builds the pages, and then reads the built HTML back and asserts that every page contains the content that gives it a reason to exist, that every canonical URL agrees with the one place the domain is configured, that no page ships executable JavaScript, and that the sitemap and the routing name the same 21 pages in both directions. If any of that fails, the new build never replaces the running one.

Where a conversion could not be checked against an authority, the range is left unclaimed rather than guessed at. There are several such gaps and they are stated on the pages where they apply: the Vietnamese zodiac animals that differ from the Chinese ones, the Tết dates for 1968 and 1969 that were Northern rather than Southern, and every date outside the ranges above.

One gap that used to be listed here has been closed. Vietnamese ages were computed from the Chinese tables until August 2026, with a note on the page admitting it; they are now computed from Vietnam's own, and the Tết reference table shows the seven years in two centuries where that changes the answer.

Sources

• Chinese lunisolar dates — Hong Kong Observatory, Gregorian–Lunar Calendar Conversion Table, ingested 2026-08-18 and committed to this site's source, so a build never depends on that server being reachable.
• Vietnamese lunisolar dates — Hồ Ngọc Đức, Âm lịch Việt Nam, ingested 2026-08-23. Computed on the 105° East meridian from 1976, and reconstructed from Prof. Hoàng Xuân Hãn's research for earlier years. Used by permission for personal, non-commercial use, which is why the commitment below about advertising is a standing commitment rather than a preference.
• Japanese era boundaries — the dates of accession, under the Era Name Act (元号法).
• Hijri, Hebrew and Solar Hijri conversions — ICU/CLDR, reached through the Intl.DateTimeFormat built into the browser and into Node. No conversion arithmetic of this site's own. The Hijri dates follow the Umm al-Qura calendar as published at ummulqura.org.sa.

  To check the method: ICU User Guide — Calendar Services; Unicode CLDR Project.

• Orbital periods — NASA Goddard Space Flight Center, planetary fact sheets, 9 bodies, sidereal periods.
• Time zones and city gazetteer — the IANA time zone database, paired with the GeoNames gazetteer covering 27,525 cities across 244 countries and 352 time zones. Licensed under Creative Commons Attribution 4.0 International (CC BY 4.0).

Privacy

A birthdate is a piece of personal information and this site treats it as one by never receiving it. There is no account, no database and no server that sees your dates: the calculation runs entirely in your browser, and the only place a birthdate is ever written down is the URL, if you choose to construct one to share.

There are no cookies, so there is no cookie banner. There is no analytics script, no advertising, no affiliate link and no request to any other host of any kind — no fonts, no images, no trackers. Every page on this site except the front one ships no JavaScript at all; the front page ships exactly one script, built here and served from here, and that script is the calculator. The build checks all of it and refuses to publish a version that breaks it, so it is not a policy that can change quietly.

Corrections

If a date here is wrong, it matters more than a wrong date usually does: reference tables get quoted, and a wrong figure that has been quoted is very hard to withdraw. Corrections are genuinely welcome, and the more specific the better — the date, what this site says, what it should say, and where that can be checked.

Write to corrections@agereckoner.com.

This applies to the descriptions as much as to the arithmetic. Several of the traditions described on this site are living ones belonging to people who will read the page, and where the site has got a custom's framing wrong rather than its dates, that is worth an email too.