How to use the date calculator
- Between two dates: pick a start and an end date to see the difference in days, in weeks and days, in years, months and days, and in business days.
- Add or subtract: pick a date, a number and a unit — days, business days, weeks, months or years — to find the resulting date, with its day of the week.
- Age: enter a date of birth to see the exact age today or on any other date, the age in days and weeks, and when the next birthday falls.
All three update as you type. Dates are calendar dates, so the results do not depend on the time of day or on your computer's time zone.
How dates are counted
Days between dates
The difference in days is the number of midnights from the start date to the end date. From 28 February to 1 March is 2 days in a leap year such as 2024 and 1 day otherwise. Many forms — hotel nights, notice periods, the duration of an event — count differently: if both the first and last day should count, add one, which the calculator also shows.
Business days
Business days are Mondays to Fridays after the start date, up to and including the end date. This is the convention used when you say "five business days from Monday": the count starts the next day. Public holidays vary by country and region and are not subtracted.
Months and years
Months have 28 to 31 days, so "one month later" needs a rule when the day does not exist. This calculator uses the rule that most calendar software and spreadsheet functions such as EDATE follow: the result is the last day of the target month. One month after 31 January 2026 is 28 February 2026; one year after 29 February 2024 is 28 February 2025. The years-months-days breakdown counts whole months first by that rule, then the remaining days.
Age and 29 February
Age is counted in completed years, months and days. People born on 29 February are treated as reaching each new age on 1 March in common years, which is the rule in the United Kingdom and Australia. Others use 28 February — New Zealand, for example, and some US states such as California. If it matters for a legal deadline, check the local rule.
Examples
| Question | Answer |
|---|---|
| Days from 28 Feb 2024 to 1 Mar 2024 | 2 (2024 is a leap year) |
| Days from Mon 28 Sep 2026 to 25 Dec 2026 | 88 days, of which 64 are business days |
| Business days from Mon 28 Sep 2026 to Fri 2 Oct 2026 | 4 |
| 31 Jan 2026 to 1 Mar 2026 | 1 month and 1 day |
| One business day after Fri 25 Sep 2026 | Mon 28 Sep 2026 |
| 10 business days after Fri 25 Sep 2026 | Fri 9 Oct 2026 |
| 100 days after 28 Sep 2026 | Wed 6 Jan 2027 |
| Age on 28 Sep 2026 of someone born 15 Jun 1990 | 36 years, 3 months, 13 days |
| Age on 28 Feb 2025 of someone born 29 Feb 2000 | 24 years, 11 months, 30 days |
Limits
- Public holidays are not excluded from business days, because they differ by country, region and sometimes employer.
- Gregorian calendar only. Dates before the calendar was adopted in a given country (1582 in Catholic Europe, 1752 in Britain, 1912 in China) are computed as if it had always applied.
- Month-end rule. Adding months uses "last day of the month" when the day is missing. Contracts sometimes define this differently; follow the contract.
- Time of day and time zones are ignored. To convert a moment between time zones, use the time zone converter.
Frequently asked questions
How many days are there between two dates?
Pick them under Between two dates. The count excludes the start date; add one if both dates should be included, which the calculator also shows.
Are weekends and holidays excluded from business days?
Weekends are. Public holidays are not, because they depend on the country and region.
What is one month after 31 January?
28 February (29 February in a leap year). When the target month is too short, the last day of that month is used.
How is age calculated for someone born on 29 February?
In common years they are treated as turning a year older on 1 March, as in the UK and Australia. New Zealand and some US states use 28 February instead.
Does my time zone affect the result?
No. The calculator works on calendar dates only.