📅 Date
Date Calculator
Measure the exact gap between two dates — or jump forward and backward through the calendar by days, weeks, months and years. Pick a mode, fill in the dates, then press Calculate.
How the date maths works
The calculator compares calendar dates in UTC, so daylight-saving changes can never shift a result by a day. The difference mode counts complete years first, then complete months, then the leftover days — the same way we describe age.
Difference mode
- Elapsed days — simply end date minus start date (the default for nights, notice periods and deadlines).
- Inclusive days — adds one so both the start and end dates count as full days.
- Business days — weekdays only, excluding Saturdays and Sundays.
- Totals in weeks, months, hours, minutes and seconds, plus the weekday of each date.
Add / subtract mode
Years and months are applied first, then weeks, then days. When the answer would land on a day that does not exist — say 31 January plus one month, or 29 February in a non-leap year — the result is clamped to the last valid day of that month, so you get 28 or 29 February rather than an error.
Handy examples
- Project deadlines: today plus 90 days.
- Rent or notice periods: 6 weeks from a given date.
- Nights in a hotel: difference between check-in and check-out, counted exclusively.
- Workdays left: business days between today and a due date.
Looking for someone's age? The Age Calculator adds a birthday countdown and total time lived.
Worked example
From 1 January 2026 to 19 October 2026 is 291 days, or 9 months and 18 days. Add 90 days to 1 January 2026 and you land on 1 April 2026.
Everyday uses
- Working out invoice and payment due dates
- Counting down to an event or deadline
- Planning project milestones and sprints
- Checking notice periods in a contract
- Measuring the gap between two historic dates
Frequently asked questions
Use the add/subtract mode from today, or the compare mode between today and 25 December 2026. The answer updates with the current date, so the only exact answer to how many days until Christmas 2026 is the one the calculator gives on the day you ask.
Same method as above with the current year's 25 December. If Christmas has already passed this year, the calculator can count forward to next year's date instead.
That depends which date in 2027 you mean. Pick the start date as today and the end date as the day in 2027 you have in mind, and the compare mode gives the exact count.
Use the add mode with +30 days from today and the calculator shows the resulting date. This is the same idea behind any 30 days from today query.
Same as above with +90 days. The calculator handles month boundaries and leap years automatically, so 90 days from today is just another add operation.
Enter your birth date and today in the compare mode. The result is the exact number of days between the two dates, which is the literal answer to how old am I in days.
It reports the difference between the two dates. Add one day if you want both endpoints counted.
Yes. The day count reflects the real calendar, including 29 February in leap years.
Yes. The add/subtract mode shifts a date forward or backward by a number of days, weeks, months or years.
No. It works with calendar dates, so a time-zone offset would not change the result.
More worked examples
- An invoice issued on 1 January with 30-day terms is due on 31 January.
- A 90-day project starting on 15 March 2026 ends on 13 June 2026.
- From 19 October 2026 to 1 January 2027 is 74 days.
- A one-year contract beginning on 29 February 2024 ends on 28 February 2025, because 2025 is not a leap year.
Common term lengths
| Period | Approximate length |
|---|---|
| 30 days | about 1 month |
| 90 days | about 3 months, a quarter |
| 180 days | about 6 months |
| 365 days | 1 common year |
| 366 days | 1 leap year |
Common date searches
| Search-style query | What this page can answer |
|---|---|
| 30 days from today | add 30 days to today's date in the add/subtract mode |
| 90 days from today | add 90 days to today and land on the future date |
| How old am I in days? | difference between your birth date and today in the compare mode |
| Days until Christmas | compare today with 25 December of the current or next year |
| Days until 2027 | compare today with 1 January 2027 |
| How many days in 2026? | a full calendar year, 365 days in a common year or 366 in a leap year |
Common mistakes to avoid
- Counting the start day as well as the end day — the difference is usually one day less than people expect.
- Assuming every month has 30 days, which drifts by a day or two over a quarter.
- Forgetting leap years when comparing dates more than four years apart.
- Mixing up 'due on' a date with 'due within' a number of days.
Further questions
Use the add/subtract mode from today, or the compare mode between today and 25 December 2026. The answer updates with the current date, so the only exact answer to how many days until Christmas 2026 is the one the calculator gives on the day you ask.
Same method as above with the current year's 25 December. If Christmas has already passed this year, the calculator can count forward to next year's date instead.
That depends which date in 2027 you mean. Pick the start date as today and the end date as the day in 2027 you have in mind, and the compare mode gives the exact count.
Use the add mode with +30 days from today and the calculator shows the resulting date. This is the same idea behind any 30 days from today query.
Same as above with +90 days. The calculator handles month boundaries and leap years automatically, so 90 days from today is just another add operation.
Enter your birth date and today in the compare mode. The result is the exact number of days between the two dates, which is the literal answer to how old am I in days.
A business day excludes weekends and public holidays, which can make a 30-day term noticeably longer in calendar terms.
366. Leap years are divisible by 4, except for century years unless they are divisible by 400.
A fixed reference point from which a system counts, such as 1 January 1970 for Unix timestamps.
Yes. This calculator works with calendar dates rather than system timestamps, so historical dates are fine.
Business days calculator, add days to date and working days calculator
A business days calculator counts Monday to Friday between two dates and ignores weekends; it does not know public holidays unless you subtract them yourself. A standard year has 260 or 261 weekdays, depending on which day 1 January falls on.
| Period | Calendar days | Business days (approx.) |
|---|---|---|
| 2 weeks | 14 | 10 |
| 30 days | 30 | 21–22 |
| 90 days | 90 | 64–65 |
| 6 months | 181–184 | 130 |
| 1 year | 365 | 260–261 |
The 30 and 90 days from today lookups are the most common date queries — use the calculator above with today's date as the start to get the exact weekday, which matters for contract deadlines and notice periods.