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Date Calculator — Days Between Dates & Date Math
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This date calculator has two modes: find the exact difference between two dates in years, months, and days, or add/subtract a number of days, weeks, months, or years from a starting date to find a future or past date. It's useful for planning deadlines, calculating contract durations, figuring out a due date, or working out how many days are left until an event. Switch modes, enter your date(s), and the result updates instantly — including a running total in days and weeks for the difference mode. Everything runs locally in your browser, so no dates or personal planning details are ever uploaded or stored. Scroll down to pick your mode and dates to see the result right away.
Features
- Calculates the difference between two dates in years, months, and days
- Adds or subtracts days, weeks, months, or years from any date
- Shows total days and weeks for quick reference
- Handles date ranges in either chronological order
- Instant recalculation as you change dates
- Useful for deadlines, durations, and event countdowns
Why use this date calculator?
- Instant results with no manual calendar counting
- Fully private — dates are never stored or uploaded
- Two calculators in one tool (difference + add/subtract)
- Simple, clear output for planning and scheduling
- Completely free with unlimited use
Frequently asked questions
How do I find the number of days between two dates?
Switch to "Days between two dates" mode, enter a start and end date, and the calculator instantly shows the difference in years, months, days, and total days.
How do I add days to a date?
Switch to "Add / subtract from a date" mode, enter your starting date, choose Add, pick a unit (days/weeks/months/years), and enter the amount.
Can I subtract days from a date to find a past date?
Yes, choose "Subtract" in add/subtract mode to go backward from the starting date by the chosen amount and unit.
Does this account for leap years?
Yes, all date math uses native JavaScript date arithmetic, which correctly accounts for leap years and varying month lengths.
What's the difference between this and the Age Calculator?
The Age Calculator is specialized for computing a person's age from a birth date to today; this Date Calculator works with any two arbitrary dates or date math.
Can I calculate months between two dates?
Yes, the difference result includes an average total-months figure alongside the precise years/months/days breakdown.