What the date calculator does One convention decides most cases: Total days (incl.) counts both ends — 6 November to 9 November is a 3 -day difference but 4 days touched.
For arithmetic on the numbers here, the standard calculator is enough; the scientific calculator handles expressions, and the life toolkit collects the other everyday tools.
How to use it 01 Calculate. Date difference takes two dates; Add/subtract dates takes a base date plus years, months and days. Below, the business row reports Total days (incl.), Workdays and Days off; ± N workdays steps a base date across whole workdays. 02 Calendar. Step month by month and click a day: Gregorian date, lunar date, ganzhi, zodiac, solar terms, ISO week and day of year. 03 World Clock. Zone cards follow the browser clock; Convert a time takes a wall time in one zone and lists it in UTC and every saved zone with its offset. 04 Countdown & Age. Enter a birth date and time, set a countdown target, or save named events locally. 05 Timestamp. One field parses a Unix value or date string and auto-detects s/ms/μs; a second converts a local date-time into a timestamp. Worked examples Readouts below come from this page; countdown and timestamp rows were captured with the page clock fixed at 2026-09-30 12:00 UTC+8.
Counts and workdays
You enter
The page reads
Difference: 2026-11-06 → 2026-11-09
0 y, 0 m, 3 d; Total days (incl.) 4 , Workdays 2 , Days off 2
Business From/To: 2026-09-30 → 2026-10-02, holidays on
Total 3 , Workdays 1 , Days off 2
Same range, holidays off
Workdays 3 , Days off 0
Base 2026-11-06, +1 workday
2026-11-09 , the following Monday
Base 2026-11-09, −1 workday
2026-11-06 , the preceding Friday
Exported to a calendar, the 9 November result is an all-day event with DTSTART 20261109 and DTEND 20261110 : RFC 5545 makes an all-day event's end exclusive, the opposite of the on-screen grid.
Leap years and the calendar
You enter
The page reads
Calendar, February 2024 / February 2025
29 / 28 day cells
Calendar, 2024-02-29
Week · DOY W9 · day 60
Calendar, 2025-02-28
W9 · day 59
Timestamp, 2024-02-29
2024-02-29T00:00:00.000Z , Unix (s) 1709164800 , 2024-W09 , DOY 60 · Q1 , Leap yes · 29
Timestamp, 2000-01-01
Leap yes — divisible by 400
Time zones and timestamps
You enter
The page reads
Convert 2026-01-15 12:00, Europe/London
UTC 2026-01-15 12:00 ; London UTC+0 ; New York Thu, Jan 15, 07:00 (UTC−5); Sydney 23:00 (UTC+11)
Convert 2026-07-15 12:00, Europe/London
UTC 2026-07-15 11:00 ; London UTC+1 ; New York Wed, Jul 15, 07:00 (UTC−4); Sydney 21:00 (UTC+10)
Convert 2026-03-29 01:30, Europe/London
UTC 2026-03-29 01:30 ; London Sun, Mar 29, 02:30 (UTC+1)
Convert 2026-10-25 01:30, Europe/London
UTC 01:30 ; London Sun, Oct 25, 01:30 (UTC+0)
Timestamp 1735689600 / 1735689600000 / 1735689600000000
s / ms / μs, all 2025-01-01T00:00:00.000Z
Timestamp 0
1970-01-01T00:00:00.000Z ; Local 1/1/1970, 08:00:00
Date → timestamp: 2026-01-01 00:00 local
2025-12-31T16:00:00.000Z , Unix (s) 1767196800
Age and countdown
Born 2000-02-29, read on 2026-09-30 12:00 UTC+8: age 26 y 7 m 1 d , Total days 9,710 , Next birthday 152 days — 1 March 2027, since 2027 has no 29 February. A countdown to 2027-01-01 00:00 reads 92d 12h 0m 0s ; the New Year preset shows 93d , a calendar-day distance, not the elapsed span.
Where the rules come from The Gregorian leap rule — divisible by 4 , except centuries unless divisible by 400 — gives 2024 and 2000 a 29 February and leaves 1900 without one. Under ISO 8601 weeks start on Monday and week 1 contains 4 January, which is how W9 holds day 60 of 2024. Timestamps count from the Unix epoch, 1970-01-01T00:00:00.000Z .
Reading the results, and their limits
Counts. Differences are calendar days, not 24-hour blocks: in a New York browser, 7–9 March 2026 still counts 2 days and the business row reads Total days (incl.) 3 .
Workdays. "CN statutory holidays" (with make-up workdays) is on by default; switch it off for a Monday–Friday week. Above roughly ten years the count stops: range too large .
Calendar arithmetic. Years first, then months, then days: 31 January 2026 plus 1 month gives 3 March 2026 , and 29 February 2024 plus 1 year gives 1 March 2025 , because the target dates do not exist in those months. There is no 1582 Julian-to-Gregorian switch here: 10 October 1582 parses as an ordinary date (1582-10-10T00:00:00.000Z ).
World Clock. Offsets come from the browser's IANA time-zone database. A wall time inside a spring-forward gap: 01:30 on 29 March 2026 in London does not exist; the table resolves it to 01:30 UTC, so the London row reads 02:30 . A fall-back time that occurs twice resolves to the later, standard-time instance.
Timestamps. Numeric input is read by digit count: 10 digits as seconds, 13 as milliseconds, 16 as microseconds. A date-only string is taken as UTC midnight: 2026-01-01 shows Local 08:00:00 in UTC+8. One date or number at a time. The fields do not parse a formula; for arithmetic on the figures a date produces, use the standard calculator . Common mistakes
Treating the Difference figure as days touched. 6–9 November is three days apart but four days inclusive; the business row counts inclusively.
Leaving CN statutory holidays on for a plain working week: 30 September to 2 October gives 1 workday with them on and 3 with the Monday–Friday rule.
Typing the same date into the two Timestamp fields. 2026-01-01 as a string is UTC midnight (Unix 1767225600 ); as a local date-time it is 2025-12-31T16:00:00.000Z (Unix 1767196800 ) in UTC+8.
Where it is used
Project scheduling. Workdays between two milestones with statutory holidays on, or a plain Monday–Friday count with them off.Age and birthdays. A birth date in Countdown & Age gives years, months, days and the next-birthday distance, including a 29 February birthday.Logs and APIs. A Unix timestamp in seconds, milliseconds or microseconds resolves to the same UTC instant, with local time shown beside it.Meetings across zones. A wall time in one zone lists in UTC and every saved zone, with spring-forward gaps resolved. Privacy Every calculation runs in your browser; no date, time zone or timestamp is uploaded. Saved zones, events and the birth date persist in local storage on this device.
Sources
ISO, ISO 8601-1:2019, Date and time — Representations for information interchange , iso.org （访问日期：2026-09-30）— date and week notation.
IANA, Time Zone Database , iana.org （访问日期：2026-09-30）— the offsets and daylight-saving transitions behind the world clock.
Wikipedia, Gregorian calendar （访问日期：2026-09-30）— the leap-year rule and the 1582 reform.
Wikipedia, Unix time （访问日期：2026-09-30）— the epoch, seconds and milliseconds.
Wikipedia, ISO week date （访问日期：2026-09-30）— week numbering for the Week · DOY card.
Calculators in this hub
Hand-picked tools, one click away. The mini versions compute live and carry your values into the full calculator.
Sources & review
Reviewed by CalcX Editorial Team
Updated 2026-09-30