Date Calculator
Count the days between two dates, add or subtract days, and find ISO week numbers — all in one place.
About this calculator
This free date calculator covers three common date tasks. Find the exact difference between two dates — in years, months, and days, plus total days, weeks, and business days (excluding weekends). Add or subtract a number of days from any date to get the resulting calendar date and day of the week. And look up the ISO week number, quarter, and how many days have passed or remain in the year for any date.
It is useful for project deadlines, notice periods, due dates, age gaps, and planning. Everything is computed locally in your browser, accounting for leap years and month lengths, with nothing uploaded.
Why use this tool
Days between dates
Find the gap in years, months, days, plus total days and business days.
Add or subtract
Shift a date forward or back by any number of days.
Week numbers
Look up ISO week numbers and quarters for any date.
Common use cases
- Count days until a deadline
- Work out a notice period or due date
- Add days to a start date
- Find business days between two dates
Frequently asked questions
Use the “Date difference” mode and pick both dates. It shows the gap in years, months, and days, plus the total days, weeks, and business days.
Switch to “Add / subtract”, choose a start date, pick add or subtract, and enter the number of days to get the resulting date and weekday.
Business days exclude weekends (Saturday and Sunday), counting only Monday to Friday between the two dates.
It is the standardised week-of-year number (1–53) used internationally, where week 1 contains the year's first Thursday.
Yes. It uses the browser's date engine, which accounts for leap years and varying month lengths.