Date & Time calculators
Age, countdowns, durations and working-day counts.
Every calculator here works with calendar dates or clock time, but they answer different questions — some find the gap between two dates, others find a date from a starting point and an offset, and others just tell you what day or week something falls on.
If you're not sure which one you need: calculators that take two dates and return a duration (Age, Date Difference, Working Days) are different from ones that take one date plus an offset and return a new date (Add or Subtract Days).
Age Calculator
Free Age Calculator. Find your exact age in years, months, days, hours, and countdown to your next birthday quickly and accurately.
Date Difference Calculator
Free Date Difference Calculator. Calculate the exact difference between two dates in days, weeks, months, and years quickly and accurately.
Countdown Calculator
Free Countdown Calculator. Count down to any future date and time with accurate days, hours, minutes, and seconds remaining.
Time Duration Calculator
Free Time Duration Calculator. Calculate the time difference between two times, including hours, minutes, and overnight durations.
Working Days Calculator
Free Business Days Calculator to calculate the number of working days between two dates, excluding weekends, quickly and accurately.
Add or Subtract Days Calculator
Free Add or Subtract Days Calculator. Find the exact date a set number of days before or after any starting date.
Week Number Calculator
Free Week Number Calculator to find the ISO week number, day of the week, and day of the year for any date.
How to choose the right calculator
- Exact age from a birth date → Age Calculator
- Number of days, months, or years between two dates → Date Difference Calculator
- Business days between two dates, excluding weekends → Working Days Calculator
- A date that's N days before or after a given date → Add or Subtract Days Calculator
- Time left until a specific future date → Countdown Calculator
- Duration between two times (hours and minutes) → Time Duration Calculator
- The ISO week number or day of the week for a date → Week Number Calculator
Frequently asked questions
Date Difference Calculator takes two dates and tells you how far apart they are. Add or Subtract Days Calculator does the reverse — it takes one date and a number of days, and tells you the resulting date. If you have two dates, use the first; if you have one date and a day count, use the second.
It excludes weekends by default and lets you account for a custom list of holidays — check that calculator's page for exactly how to enter them.
It's mainly useful for week-based planning systems — manufacturing, logistics, or payroll cycles that reference a specific ISO week number rather than a calendar date range.