Date Calculators
Date calculators answer questions about gaps and offsets: how many days lie between two dates, what date falls 90 days after an invoice, how old someone is on a given day, or how many working days a project has.
Each calculator states exactly how it counts. Whether the start or end date is included, how a month-end is handled and which days count as working days are visible choices, not hidden assumptions, because these details are what make two calculators disagree.
Tools in this category
Date Difference Calculate the exact difference between two dates in days, weeks, months and years. Add or Subtract Days Add or subtract days, weeks, months or years from any date. Age Calculator Find exact age in years, months and days from a date of birth. Business Days Count the working days between two dates, excluding weekends and holidays you choose. Add Business Days Find the date that falls a set number of working days from a start date. Day of the Week Find out which day of the week any date falls on. Quarter Calculator Find which calendar quarter a date is in, and when it starts and ends.
Which tool do you need?
- How long is it between two dates? Use the Date Difference calculator for days, weeks, months and years.
- What date is 30 days, 6 weeks or 3 months from now? Use Add or Subtract Days to move a date forward or back.
- How old is someone, exactly? The Age Calculator gives years, months and days and the next birthday.
- How many working days are there between two dates? Business Days excludes weekends and any holidays you list.
- What date is 10 working days away? Add Business Days skips weekends and holidays to find the date.
- Which weekday is a particular date? Day of the Week also shows the day number and ISO week.
- Which quarter is a date in? The Quarter Calculator gives the quarter and its start and end.
Good to know
All results are based on the Gregorian calendar and whole calendar dates. None of these tools take a time of day or a time zone into account; the Time Zone Tools do.
Background reading
- The Gregorian calendar The calendar most of the world uses for civil dates: where it came from, how it differs from the Julian calendar, and how dates before 1582 are handled.
- Leap years The three-part Gregorian leap-year rule, why century years are different, a list of leap years, and what 29 February does to date arithmetic.
- Days in each month A table of month lengths, the day of the year each month starts on, quarter lengths, and how to remember which months have 30 or 31 days.
- ISO week numbers How ISO 8601 numbers weeks, why a year can have 53 weeks, why 1 January can belong to the previous year, and how ISO weeks differ from other week numbering.
- Counting days between dates Why two people can count the same date range and get different answers: inclusive and exclusive counting, calendar days versus elapsed time, and month-based spans.
- Adding months and years What "one month after 31 January" means, why adding months in steps can give a different answer, and how spreadsheets and programming languages disagree.
- Business days What counts as a business day, how weekends and holidays are excluded, the counting conventions behind deadlines, and how spreadsheet functions compare.