Date Calculator
Calculate the number of days, weeks, or months between two dates.
A date calculator - or day calculator, or date to date calculator - finds the exact number of days, weeks, months, or years between two dates, or adds/subtracts a duration from a starting date to find a resulting date. Unlike simple month-counting, this tool accounts for actual calendar irregularities - different month lengths and leap years - so the result is exact rather than approximate.
Enter a start date and end date to find the days between two dates, or enter a start date plus a number of days/weeks/months to add or subtract to find a resulting date.
Worked Calculation Examples
| Scenario | Result | Calculation Step |
|---|---|---|
| Days between Jan 1, 2026 and Dec 31, 2026 | 364 Days | Exactly 364 days apart (52 weeks). |
Why Calendar Math Isn't Simple Subtraction
Months have different lengths (28 to 31 days), and leap years add an extra day roughly every four years (with exceptions for century years not divisible by 400), which means you can't just multiply 'number of months' by 30 and get an accurate day count. This calculator works with actual calendar dates internally, so a duration spanning February in a leap year, or crossing multiple months of different lengths, still produces an exact day count.
The Leap Year Rule
A year is a leap year if it is divisible by 4, except century years (divisible by 100), which are only leap years if also divisible by 400. This is why 2000 was a leap year but 1900 was not, despite both being divisible by 100 - a detail that matters for any date calculation spanning a century boundary, though this is rare in everyday use.
Common Uses for Date Duration Calculations
Date calculations come up constantly in practical planning: figuring out how many days until a deadline or event, calculating the exact length of an employment period or lease, determining an age in days for a medical or legal context, or finding what date falls a certain number of days from today for scheduling purposes.
How to Use the Date Calculator
- Open the Date Calculator and enter the values requested in the input fields.
- Check the units, percentages, dates, or time periods before reading the answer.
- Review the instant result and adjust any value to compare another scenario.
- Use the formula, example, and FAQs below to understand how the date calculator works.
Frequently Asked Questions
Does this account for leap years?
Yes, full calendar dates accurately handle leap years and variable month lengths, so results are exact even across February in a leap year or century boundaries.
How many days are in a year?
A standard year has 365 days; a leap year has 366, with the extra day added as February 29. Leap years occur roughly every 4 years, following the standard leap year rule.
What date will it be 90 days from today?
Enter today's date and add 90 days using this calculator to get the exact resulting date, accounting for the actual number of days in each month it spans.
How do I calculate the exact duration between two dates in years, months, and days?
Enter both dates as the start and end date - the calculator breaks down the total duration into years, months, and remaining days rather than just a total day count.
Why might two 'months' calculations give different day counts?
Because months vary in length (28-31 days), a duration described as '2 months' starting in different months of the year can span a different actual number of days.
Can I subtract time from a date instead of adding it?
Yes, you can calculate a date a certain number of days, weeks, months, or years before a given date, not just after it.
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Last updated: September 29, 2026.