Date Calculator

Purpose

Online date calculator supporting date-difference (days/hours/minutes/seconds), date arithmetic (add/subtract days/weeks/months/years), workday calculation (excluding weekends and custom holidays), Chinese lunar/Gregorian conversion. Handles timezones, leap years, end-of-month edge cases. Common for contract expiry, project duration estimation, age calculation, birthday reminders, visa validity, SLA deadlines. All calculation runs locally.

Steps

1. Mode 1: difference — pick start and end date, get days/hours/minutes/seconds
2. Mode 2: add/subtract — pick base date, input +30 days / -3 months, get result
3. Mode 3: workdays — exclude weekends (plus custom holiday list)
4. Mode 4: lunar/Gregorian — 2026-01-01 ↔ Chinese 乙巳年正月初一
5. Difference output: multi-unit (89 days = 12 weeks 5 days = 0.24 years)
6. Timezone: default local, can switch to UTC or specific timezone
7. Leap year: Feb 29 + 1 year = Mar 1 (no leap day) or Feb 28 (conservative)
8. Export result / one-click copy

FAQ

How to calculate age difference between two people?

"Age difference" by birth year (ignoring month/day) is common. For exact "years, months, days" use date-difference with custom units. Note: actual age increments on birthday in Western convention; Chinese tradition counts from birth as 1 and increments on Lunar New Year.

How does adding 1 month at end of month work? Jan 31 + 1 month = ?

Tool defaults to "nearest last day": Jan 31 + 1 month = Feb 28/29 (last day of that month). Strict mode adds 30 days. Legal/contract scenarios usually use "nearest last day". Toggle between modes.

How to exclude Chinese holidays from workday calculation?

Built-in Chinese statutory holidays (Spring Festival, Qingming, Labor, Dragon Boat, Mid-Autumn, National Day, with 2020-2026 makeup/transfer arrangements). Custom holiday lists also supported (one date per line). Note: makeup days off (e.g., Qingming moved to Monday) and compensatory workdays (working a weekend) — tool follows official announcements.

How are lunar leap months calculated? Which month is leap in 2025?

Lunar leap months are astronomically determined (avoid spring/autumn equinox drift), about 7 in 19 years. 2025 has leap 6th month (two 6th lunar months). The tool follows the Lunar/Chinese Calendar standard for 1900-2100. Birthday tracking and traditional festivals (Mid-Autumn, Dragon Boat) all accurate.

Why does my date+3-months result differ from someone else's by a day?

Usually timezone or leap year. Timezone: crossing the date line gives 24-hour shift; use UTC to eliminate. Leap year: 2020-02-28 + 1 year = 2021-02-28 (Feb 29 does not exist). If original is 2020-02-29, tool uses "nearest legal date" rule (2021-02-28).

Use cases

• Contract expiry: sign date + 12 months = expiry date
• Project duration: start-end date → workday count (excluding weekends and holidays)
• Precise age: from birth date to today, years/months/days
• Visa/passport validity check
• SLA: 4-hour response (within business hours)

Use cases

Contract expiry, project duration, age calculation, visa validity, SLA deadlines. Legal, HR, PM, sales. Multi-mode (diff/add/workdays/lunar), holiday exclusion, end-of-month rules, leap year are the differentiators.