Date Calculator
Privacy-first date calculator: difference, age, workdays, add/subtract, day-of-week — all modes in one tool with custom holidays and shareable URLs.
Zero upload. Local computation.
Frequently asked questions
Is the inclusive setting on or off by default?
Off. From 2026-01-01 to 2026-01-02 returns 1 day. Turn it on to count both endpoints (2 days).
Why do months handle Jan 31 + 1 month as Mar 3?
JavaScript's Date overflows automatically. We add a hint when this overflow happens; some tools call this 'rolling' behavior.
Which Chinese holidays are included in the CN preset?
New Year's Day, Spring Festival, Tomb-Sweeping, Labour Day, Dragon Boat, Mid-Autumn, and National Day, with lunar dates pre-resolved to Gregorian for 2020–2030.
How accurate is the lunar age (虚岁) calculation?
We use a 1900–2100 table of Spring Festival dates. The age is calculated as currentLunarYear − birthLunarYear + 1.
Why does Saturday default to non-working?
Most jurisdictions count only Mon–Fri as working days. Toggle 'Treat Saturday as workday' for retail / hospitality scenarios.
Is my data sent anywhere?
No. All computation runs in your browser; no network request carries your dates.
Can I share a result?
Yes. Click 'Share link' — the URL hash encodes all inputs, opening the same result on any device.
What's the date range supported?
Roughly 1583 (start of Gregorian calendar) to 9999. Dates before 1583 are calculated proleptically — usable but not historically accurate. Full lunar month/day conversion is planned for V1.1.
Related Tools
Timestamp
Convert between Unix epoch timestamps (s/ms/μs/ns) and human-readable date strings. Auto-unit detection, multi time-zone view, batch parsing — entirely client-side.
Word Counter
Free privacy-first word and character counter with reading time, keyword density, and readability — no upload, runs in your browser.
Unit Converter
Convert across 12 categories and 100+ units — length, weight, temperature, volume, area, speed, time, energy, pressure, power, angle, and digital data — instantly in your browser.