Calculate exact age on any date
Pick a birth date and a reference date — get the years/months/days plus total weeks, days, hours and minutes lived.
How age math works
Calendar-aware: years roll only when the month and day are reached. Day borrow uses the previous month's actual length so 28/29/30/31 are handled.
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Enter DOB
Any date in your timezone.
Parsing accepts ISO 8601, RFC 3339, RFC 2822, and Unix epoch seconds/milliseconds. The Date constructor handles the rest with browser-engine consistency.
inputISO 8601RFC 3339epochlivein · timestampDOB · ISO1990-04-12
loaded · ISO 8601zone · ready - 02
Pick reference
Defaults to today — change to compute the age on any date.
All math runs in UTC internally to avoid DST landmines; presentation converts back to the user’s zone via
Intl.DateTimeFormat.onUTC mathIntlDST-safeliveon · optionsdate · live2026-05-21
options applied · UTCDST-safe - 03
Borrow logic
If the day is negative, we borrow days from the previous calendar month.
Output respects the chosen timezone offset (
Zvs+05:30) and pads digits per ISO conventions so sorts stay chronological.calendaroffsetzone-awaresortablepaddedborrow · computedmonth · ready31, 30, 28 vary
computed · instantsortable - 04
All units
Total months, weeks, days, hours and minutes are shown.
Copy writes via the Async Clipboard API; nothing pings a time server — the browser’s clock is the only oracle.
unitsclipboardno oracledeterministicclient-side✓ · copiedready · done✓ Copied
shipped · ready to shipsuccess
Time math without DST landmines
Always store UTC
Convert to local for display only. UTC storage avoids DST jumps and timezone drift in databases.
Watch leap seconds
POSIX time doesn’t count leap seconds; some systems do. Don’t use timestamps for sub-second precision across boundaries.
Prefer Temporal eventually
The Date API has many quirks. Temporal is shipping in modern engines and handles zones correctly.
Cron is timezone-tricky
Cron expressions run in the daemon’s local zone unless told otherwise. Pin a TZ explicitly for predictable runs.
ISO 8601 sorts naturally
YYYY-MM-DDTHH:mm:ss sorts correctly as a string. Don’t use US-style MM/DD/YYYY for anything machine-readable.
Beware Y2K38
Signed 32-bit Unix timestamps overflow in 2038. Use 64-bit storage end-to-end for long-lived systems.
When to compute age
Birthdays, contracts, milestones.
Forms
Age-gate flows that need DOB validation. Math runs in UTC under the hood to dodge DST jumps — local time is only for display. That means scheduling logic and date diffs survive March / November fall-back without the classic off-by-one-hour bug.
DST-safeContracts
Years of service on a future review date. Browser clock is the only source — no external time server, no privacy leak, no rate limit. Pair with NTP-synced server time for high-accuracy use cases, but for human-scale work the browser clock is plenty.
UTC-correctMilestones
Plan a 10000-day birthday party. ISO 8601 output sorts naturally as strings, perfect for filenames (report-2026-01-15.pdf) and log lines that need chronological ordering without parsing. Drop into S3 keys for free time-bucketing.
ISO-sortableTest fixtures
Anchor expected ages relative to a stable reference date. Pairs cleanly with cron, scheduled tasks, and timestamped log analysis. The tool's output drops directly into APScheduler, Linux cron, or GitHub Actions schedule expressions without re-formatting.
spec-gradePension math
How many months until eligibility? Output respects the chosen timezone offset (Z vs +05:30) so REST APIs and database TIMESTAMP WITH TIME ZONE columns round-trip cleanly. No ambiguity between "noon UTC" and "noon local".
zone-awareInsurance
Quote builders that take age on a date. Confirms the difference between epoch seconds (10 digits) and milliseconds (13 digits) before you commit code that mis-multiplies by 1000 — a classic bug in cross-language time handling.
epoch-accurateFrequently asked questions
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