Date & calendar tool

Date Calculator

Calculate the number of days between two dates, view the difference in years, months and days, or add and subtract days, weeks, months and years from any calendar date.

Days between datesAdd / subtract datesLeap-year awareRuns in your browser

Calculate days between two dates

Enter any two calendar dates. The result shows both total days and a calendar breakdown.

Use inclusive counting for schedules where both boundary dates count. Standard elapsed-day counting is the default.

Date difference0 days

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Calendar breakdown—
Weeks + days—
Inclusive count—
Start weekday—
End weekday—
Direction—

Add or subtract time from a date

Choose a starting date, operation, number and calendar unit.

When a month or year does not contain the original day, the result is clamped to the last valid day of that month.

Resulting date—

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Weekday—
Start date—
Operation—

How to use the Date Calculator

1

Choose the calculation

Select either days between dates or add/subtract date.

2

Enter your dates and values

Use the calendar fields and choose inclusive counting only when both boundary dates should count.

3

Read the breakdown

View total days, calendar years/months/days, weekdays or the resulting date.

How to calculate days between two dates

The standard difference between two dates measures the elapsed calendar days from the start date to the end date. For example, the difference from October 1 to October 2 is one elapsed day.

If you need to count both October 1 and October 2 as part of a schedule, use the inclusive days option. In that example, the inclusive count is two days.

Start dateEnd dateElapsed daysInclusive days
1 Oct 20262 Oct 202612
1 Oct 20268 Oct 202678
1 Jan 20261 Feb 20263132

Calendar difference vs total days

A result such as 1 year, 2 months and 5 days is a calendar breakdown. A result such as 431 days is the total elapsed-day count. Both can describe the same interval, but they answer different questions.

  • Total days is useful for countdowns, deadlines and elapsed-time tracking.
  • Years, months and days is easier for human-readable calendar intervals.
  • Weeks and days can be useful for schedules measured in seven-day periods.

Add or subtract days, weeks, months and years

The second calculator moves a date forward or backward by the amount you enter. Days and weeks are added as fixed calendar-day intervals. Months and years are calendar operations, so month length matters.

For example, adding one month to January 31 cannot produce February 31. This calculator clamps the result to the final valid day of the target month instead of silently overflowing into March.

CalculationResultWhy
10 Oct 2026 + 10 days20 Oct 2026Adds ten calendar days
10 Oct 2026 − 2 weeks26 Sep 2026Subtracts 14 calendar days
31 Jan 2026 + 1 month28 Feb 2026Clamped to the last valid day of February
29 Feb 2024 + 1 year28 Feb 20252025 is not a leap year

Leap years and month lengths

Calendar calculations need to account for February, leap years and months with 30 or 31 days. A leap year normally has 366 days, with February 29 added to the calendar. These differences are why a calendar-aware calculator is more reliable than assuming every month has the same length.

Note: This page works with calendar dates, not times of day. For business-day schedules, weekends or holiday rules, use a dedicated business-day calculator because those rules are separate from ordinary calendar arithmetic.

Common uses for a date calculator

  • Deadlines and project planning: measure calendar days between a start date and due date.
  • Events and countdowns: find how many days remain before a wedding, trip, exam or launch.
  • Contracts and subscriptions: calculate a future date after a stated number of days or months.
  • Personal planning: move backward or forward from a known date to find another milestone.
  • Record checking: compare two calendar dates with an exact year-month-day breakdown.

Common date-calculation mistakes

  • Mixing inclusive and elapsed counting: decide whether both boundary dates should count.
  • Assuming every month has 30 days: actual calendar months vary from 28 to 31 days.
  • Ignoring leap years: February can contain 29 days.
  • Using simple month arithmetic at month-end: dates such as January 31 require clamping when the target month is shorter.
  • Using calendar days for work schedules: ordinary date difference does not automatically exclude weekends or holidays.

Related date calculators

Day CounterCount the days between two dates. Business Days CalculatorCount weekdays between two dates. Add Business DaysMove forward or backward by workdays. Age CalculatorCalculate exact age from date of birth.

Frequently Asked Questions

How do I calculate the number of days between two dates?

Enter the start and end dates and select Calculate difference. The result shows elapsed days plus a calendar breakdown.

What is inclusive date counting?

Inclusive counting includes both the start date and end date. Standard elapsed-day counting measures the distance between them and excludes one endpoint.

Can I subtract dates as well as add them?

Yes. In the Add / subtract date tab, choose Subtract and select days, weeks, months or years.

What happens when I add one month to January 31?

The calculator clamps the result to the final valid day of the target month. For example, January 31, 2026 plus one month becomes February 28, 2026.

Does this calculator include weekends?

Yes. This is a calendar-date calculator, so ordinary day differences include weekends. Use the Business Days Calculator when you want weekday-based counts.

Are my entered dates stored?

The calculations run in your browser. The entered dates do not need to be sent to a server to produce the result.

Last updated: October 18, 2026. Calendar calculations on this page do not automatically apply business-day, holiday, legal or contractual counting rules.