Online Date Calculator
Date difference / date add & subtract / weekday / leap year — all in one
Date interval
Add or subtract
Weekday lookup
Leap year check
Common use cases
The date calculator covers many everyday and planning needs: project duration — fill project start and end dates in "Date difference" to see the whole years, months and days spanned; contract expiry / membership validity — push months or days forward from the signing date in "Date add/subtract"; anniversary and due-date countdown — set the target as the end date and watch "X days remaining" update live; what date is N days from now — set today as the base and push forward 30/100/180 days. See the 2026 holiday schedule for the full year's holidays.
Related calculators
For more date tools: the workday calculator counts days excluding weekends and statutory holidays; the age calculator computes exact age, nominal age, constellation and zodiac; the scientific calculator supports 16 math functions including trigonometry, logs and powers; the binary code calculator converts decimal integers to sign-magnitude, one's-complement and two's-complement.
How to use
Calculate the exact interval between two dates (years/months/days/weeks/days/hours/minutes) as a day-interval or time-interval calculator, or add/subtract dates forward or backward. The weekday query also returns the lunar date, ganzhi, zodiac and solar-term info.
Why leap years have 366 days
The Earth takes about 365.2422 days to orbit the Sun — about 0.2422 days (roughly 5h48m) more than a 365-day year. If every year were 365 days, the calendar would slowly drift out of sync with the seasons. So every few years we add an extra day, making February 29 and a 366-day leap year. The rule: years divisible by 4 but not by 100 are leap years, and years divisible by 400 are also leap years (2000 was a leap year, 1900 was not). When you do month arithmetic in this calculator, February is clamped to 28 or 29 depending on whether the year is a leap year, so the result date always exists.
What is a date calculator?
A date calculator is an online tool that quickly handles conversions between a date and a number: give a base date plus an offset and it returns the target date and weekday, or give two dates and it returns the exact years/months/days between them. It condenses what used to require flipping calendars, counting fingers or writing code into a few clicks. Beyond basic calculations, this tool also returns the lunar date, ganzhi, zodiac and solar term, helping you plan around traditional festivals.
Date calculation vs date add/subtract
The two are often used interchangeably but differ in emphasis: date add/subtract starts from a known date and shifts forward or backward by days/weeks/months/years to another concrete date (e.g. "what is 100 days from today"); date calculation is the broader term covering both add/subtract and the reverse interval calculation (e.g. "how many days from project start to deadline"). In this calculator these map to the "Date add/subtract" and "Date difference" sections respectively — together with the weekday query and "Leap year check" they cover most daily planning needs.
Common date-calculation mistakes
Watch out for these before you calculate:
- Whether the end date counts: by default "Difference" counts only up to the day before the end date. For event or contract durations where both endpoints count, add +1 day to the result or you will be a day short.
- Calendar days ≠ working days: 30 calendar days apart is not 30 working days — weekends and statutory holidays are in between. Compute "actual working days" separately with the workday option.
- Month-end boundaries: adding 1 month to Jan 31 does not yield Feb 31; the tool clamps to the last valid day of February, important when crossing months.
- February 29 only in leap years: adding a year to a Feb 29 in a leap year lands on Feb 28 in a common year.
- First week of the year: under ISO 8601 (Monday-based), the first days of January can belong to week 52/53 of the previous year — normal, not an error.
FAQ
How many days are there between two dates?
Pick a start and end date in the "Date difference" section and the tool automatically shows the year/month/day breakdown, total days, total hours and total minutes. Results include both a detailed split (e.g. "2y 3m 15d") and a plain day count.
How do I find the exact difference in years, months and days?
After choosing the start and end dates in the "Date difference" section, the "Difference" row gives a "Xy Ym Zd" split, with total days, weeks and hours below for other contexts. Set the start to a project kickoff and the end to a deadline, and you instantly see how many whole years, months and days it spans.
Which units are supported for date add/subtract?
Days, weeks, months and years are supported, going forward or backward. For example 2024-01-15 + 30 days = 2024-02-14, + 2 weeks = 2024-01-29. Month arithmetic clamps to the last day of the target month: 2024-01-31 + 1 month = 2024-02-29, 2023-01-31 + 1 month = 2023-02-28.
How do I check whether a year is a leap year?
Enter a year in the "Leap year check" section. Rules: a year divisible by 4 but not by 100 is a leap year; a year divisible by 400 is also a leap year. Leap years have 366 days (Feb 29); common years have 365. Common leap years include 2024 and 2028.
Does the result include working-day information?
Tick "Working days only" in the "Date difference" section and the result also shows workdays after automatically excluding weekends and statutory holidays (including swapped make-up days), while still showing the weekday, year/month/day split and total days. For a full breakdown of holidays/weekends/make-up days, paid leave and per-month workday stats, use the workday calculator. To calculate age, use the age calculator.
How do I count down to a specific date?
Set the start date to today and the end date to any target in the "Date difference" section; the result shows "X days Yh Zm Zs remaining to the end date" and updates in real time. If the target has passed it shows "X days elapsed". Great for anniversaries, deadlines and exams.
How do I find which week of the year a date falls in?
Enter any date in the "Weekday query" section and it also returns the ISO 8601 week number (Monday-based). Days early in the year can belong to the final week of the previous year — a normal part of the international standard.
What date is 100 days from now?
In the "Date add/subtract" section set today as the base (tap the Today button), choose Forward, unit Days, amount 100, and the result gives the date and weekday. The same method works for any N: 30, 180, 365 days and so on.
How do I calculate a contract expiry date or membership validity?
In "Date add/subtract", use the signing or activation date as the base, choose Forward, and add days or months per the contract/membership (e.g. 365 days, 12 months) to get the exact expiry date and weekday. Feed that date back into "Date difference" to see how many days remain.
How do I count down to an anniversary or baby due date?
Set the start date to today and the end date to the anniversary or due date in the "Date difference" section; the result shows "X days Yh Zm Zs remaining" in real time. For a due date you can also use the add/subtract tool: last menstrual period + 280 days (40 weeks).
How many days until the end of the year or Spring Festival?
Set today as the start and Dec 31 of the current year (for year-end) or your target Spring Festival date as the end in the "Date difference" section to see total days and a live countdown, plus a year/month/day split and total weeks for planning.
How many hours and minutes are between two dates?
After choosing the start and end dates, the result shows total hours and total minutes (e.g. 3 days = 72 hours = 4320 minutes). For precision down to a specific hour/minute, include the time in the end date before calculating.
How many days have I lived since birth?
Set the start date to your birthdate and the end date to today in the "Date difference" section; the "Difference" row equals your total days alive, with total hours/minutes below. For exact age, nominal age, zodiac and constellation, use the age calculator.
How many weeks between two dates?
After choosing the start and end dates, the result gives a "Xw + Yd" week split (e.g. 23 days = 3w + 2d) plus total days, hours and minutes, useful for weekly planning and scheduling.
How do I look up the lunar date and weekday of a given day?
Enter any date (e.g. a birthday) in the "Weekday query" section; the result shows the weekday, lunar date, ganzhi (Heavenly Stems and Earthly Branches) and zodiac, and marks the solar term if any. Set next birthday as the end date in "Date difference" for a live countdown.
What animal year is this? How do I check a date's zodiac?
The zodiac cycles by lunar year (Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog, Pig — a 12-year cycle). Enter any date in the "Weekday query" to see its zodiac, or use the age calculator for your own. Note the zodiac changes at Chinese New Year, so births before it still belong to the previous year.
What does ganzhi mean, and how do I read it?
The ganzhi pairs 10 Heavenly Stems (jia, yi, bing…) with 12 Earthly Branches (zi, chou, yin…) on a 60-year cycle for counting years and days. The "Weekday query" and "Date add/subtract" results show the day's ganzhi (e.g. "Bingwu Year, Jiazi Day"). Explore further with the Chinese almanac.
How do I convert a solar date to a lunar date?
Enter a solar date in the "Weekday query" and it directly shows the corresponding lunar date (e.g. for your birthday or anniversary). To go the other way or check traditions and auspicious/inauspicious info, use the Chinese almanac. Combine with the age calculator for exact age, nominal age and constellation.