Free Date & Time Calculators
Calculate durations, add or subtract dates, work out hours between times, and find week numbers - free date and time tools.
About Date & Time Tools
Count the gap between two dates with the Date Duration Calculator, project a deadline with Date Add / Subtract, total hours (including overnight shifts) with the Time Duration Calculator, or find any date's ISO week number.
Each tool handles leap years and month lengths correctly, so the results are exact rather than approximate.
The questions these tools answer
Date arithmetic looks trivial and contains several genuine ambiguities. Months have unequal lengths, so ‘one month after 31 January’ has no single correct answer — most software and most legal drafting clamp to 28 or 29 February, while some implementations overflow into March. Leap years follow a three-part rule: divisible by four, except centuries, unless divisible by 400. And the difference between two dates is either inclusive or exclusive of the endpoints, which changes the answer by a day.
Inclusive or exclusive
From 1 March to 5 March is four days as a difference and five days counting both ends. Elapsed time, interest and age use the exclusive count; hotel nights, leave requests and event durations use the inclusive one. Contracts and payroll rules usually specify which applies, and that single day regularly decides whether a filing is on time or a day is paid.
Working days and holidays
Excluding weekends is straightforward arithmetic. Excluding public holidays is not, because holiday calendars are national and regional, some move with the lunar or ecclesiastical calendar, and governments occasionally declare one-off holidays at short notice. ‘Ten working days’ means different dates in different countries, and legal deadlines are unforgiving about it — check the calendar for the specific jurisdiction rather than the country.
Time zones and week numbers
Day counts are unaffected by time zones; hour counts are not, since a day containing a daylight saving transition is 23 or 25 hours long. Week numbering has its own surprises: under ISO 8601 a year can have 53 weeks, and 1 January sometimes falls in the final week of the previous year. Reporting systems that assume week 1 always starts in January produce a spurious week 0 every few Januarys.
Frequently Asked Questions
Do the date tools handle leap years?
Yes. They use real calendar dates, so leap years and different month lengths are accounted for.
Can I count only business days?
Yes. The Date Duration Calculator offers a working-day count that excludes weekends.
Can it handle overnight time spans?
Yes. The Time Duration Calculator correctly handles times that cross midnight.
Should I count both the start and end dates?
It depends what you are measuring. Elapsed time, interest and age use the exclusive count; hotel nights, leave and event durations use the inclusive one. Contracts usually specify, and the one-day difference frequently matters.
What is one month after 31 January?
28 February, or 29 in a leap year, under the clamping convention used by most software and legal drafting. When exactness matters, count in days rather than months.
Why does my dashboard show a week 0 in January?
Because it assumes week 1 always begins in January rather than following the ISO 8601 rule, where week 1 is the week containing the first Thursday. Days in the previous year's final week then get no valid number.