Best Free Online Developer Tools to Use in 2026
A practical, opinionated list of the best free online developer tools worth using in 2026, organized by category so you can find what you need fast.
Aug 08, 2026
Date Calculator
Add or subtract days, weeks, months, and years from any date. Or calculate the exact difference between two dates.
Date Calculator
Select a start date to calculate
What is Date Calculator?
A Date Calculator is a tool that performs arithmetic operations on dates — adding or subtracting days, weeks, months, and years from a given date, or calculating the exact difference between two dates. It handles calendar complexities like leap years and varying month lengths automatically.
Date calculators are used in project planning to determine deadlines and milestones, in HR for calculating leave balances and tenure, in finance for due dates and maturity periods, and in everyday life for event planning and age calculations. The results include detailed information such as the day of the week, ISO week number, and the exact duration breakdown in years, months, and days.
- Choose a mode — "Add / Subtract" to calculate a future or past date, or "Date Difference" to find the gap between two dates.
- Select dates — Pick a start date using the date picker. For difference mode, also pick an end date.
- Enter values — In add/subtract mode, enter the number of years, months, weeks, and/or days to add or subtract.
- View results — See the calculated date with detailed information including day of week, week number, and ISO format.
How does the calculator handle leap years?
The calculator correctly accounts for leap years (February 29). When adding months to a date like January 31, if the target month has fewer days (e.g., February), it adjusts to the last day of that month (February 28 or 29).
Does weeks × 7 equal exactly 7 days?
Yes. Weeks are converted to days (1 week = 7 days) and added to the day count. This is separate from months and years, which are calculated based on calendar months.
What is the maximum range?
You can add or subtract up to 1,000 years, 120 months, 5,200 weeks, and 36,500 days. The calculator works with dates from year 1 to year 9999.
Does the date difference include the end date?
Yes. The difference calculation includes the end date. For example, the difference between January 1 and January 2 is 1 day. If you need to exclude the end date, subtract 1 from the total.
Last updated: 17 Aug 2026
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