Date Calculator
Measure the gap between two calendar dates, or move a date forward and backward by days, weeks, months, quarters, or years.
Your result will appear here
Pick two dates to see the gap, or add and subtract days, weeks, months, or years from a date.
Which time tool should you use?
- Need the difference in hours and minutes rather than days? Use the Time Duration Calculator.
- Adding or subtracting time to a specific date and time? Use the Time Calculator.
Quick Answer
This calculator works with calendar dates. It finds the difference between two dates in years, months, weeks, and days, or adds and subtracts calendar units from a date to give you a new one — with leap years, month lengths, and ISO week numbers handled for you.
How It Works: Formula & Variables
Difference = End Date − Start Date · New Date = Start Date ± Calendar Units
- Common year
- 365 days.
- Leap year
- 366 days — divisible by 4, except century years that are not divisible by 400.
- ISO week
- Monday to Sunday, numbered 1–53; week 1 is the week containing January 4.
- Formats
- US (mm/dd/yyyy), EU (dd/mm/yyyy), and ISO 8601 (yyyy-mm-dd) are all shown.
Worked Examples
Example 1: Difference between two dates
From September 4, 1999 to January 2, 2003 there are three full years (1999 through 2002, which includes the 2000 leap year) worth 1,096 days, plus another 120 days through the autumn and into early January. That works out to 1,216 days between the two dates, or 1,217 days if you count the end date as well — roughly three years and four months.
Example 2: What date is 90 days from today?
Set the start date to today, choose days as the unit, and add 90. The tool returns the resulting date along with its weekday and ISO week number. To count backward instead, switch the operation to subtract.
Key Concepts
Months are not a fixed length: They run from 28 to 31 days, so a "one month" jump lands on a different day depending on where you start. Adding a month to January 31 lands at the end of February, not on a 31st that does not exist.
Including the end date shifts the total by one: Whether you count the last day changes the answer by exactly one day, so it helps to be clear about which convention a deadline uses.
Date formats are easy to misread: 03/04/2026 is March 4 in the US notation and April 3 in the EU one. The result panel spells the date out and shows all three formats to remove the doubt.
Common Mistakes
Treating every month as 30 days: Month lengths vary, so a rough "30 days a month" estimate drifts further off the longer the span.
Forgetting leap years: Skipping February 29 quietly undercounts any range that crosses a leap day.
Mixing up US and EU notation: Reading 03/04/2026 in the wrong order shifts a date by a month or more.
Frequently Asked Questions
Enter both dates and the calculator counts the actual calendar days between them, so leap years and the different lengths of each month are already handled for you. You also get the gap expressed in years, months, and weeks.
Switch to the "Add / subtract" tab, put in a starting date, choose days as the unit, and enter the number you want to move forward. Pick "Subtract" instead to count backwards to an earlier date.
By default the end date is included in the total, which is what most people expect when they ask how many days something covers. Untick that option to count the gap between the dates instead, which comes out one day shorter.
A year is a leap year when it divides evenly by 4, except for century years, which only count if they also divide by 400. That is why 2000 was a leap year but 1900 was not.
ISO weeks run Monday to Sunday and are numbered 1 to 53, and week 1 is always the week that contains January 4. The "Add / subtract" result shows the ISO week for the date you land on.
The plain day count includes every calendar day. Tick "business days only" to also see the count with Saturdays and Sundays removed. Public holidays vary by country, so they are not removed automatically.
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