Date Calculator
Find the exact number of days between two dates, count weekdays, or add and subtract calendar durations. Calculations use calendar dates rather than local clock time, so daylight-saving changes do not alter the answer.
Date calculation formulas
For two calendar dates, the elapsed-day result is the later date’s UTC date serial minus the earlier date’s serial. Using date-only UTC values prevents a 23-hour or 25-hour daylight-saving day from changing the result.
Elapsed days = end-date serial − start-date serial. When “include the end date” is selected, one calendar day is added to the absolute duration. The business-day result counts Monday through Friday only.
When adding years or months, this calculator preserves the day of the month when possible. If that day does not exist, it uses the month’s final day. For example, January 31 plus one month becomes February 28 in a common year or February 29 in a leap year.
Checked examples
| Input | Result | Reason |
|---|---|---|
| September 1 to September 15, 2026 | 14 days | Standard elapsed-date difference |
| February 28 to March 1, 2024 | 2 days | 2024 includes February 29 |
| Same date, inclusive | 1 day | The shared calendar date is counted |
| Monday to Friday | 4 weekdays, or 5 inclusive | The end date is excluded unless selected |
| January 31, 2024 + 1 month | February 29, 2024 | Leap-year end-of-month clamp |
| February 29, 2024 + 1 year | February 28, 2025 | 2025 has no February 29 |
How to use the Date Calculator
- Choose whether to compare two dates or add/subtract a duration.
- Enter complete calendar dates.
- For a difference, decide whether the end date should be included.
- For date arithmetic, enter whole years, months, weeks or days; use a minus sign to subtract.
- Select Calculate date and review the calendar result and assumptions.
Limits and interpretation
- Supported dates run from 1600 through 2400.
- Business days exclude Saturdays and Sundays only. They do not remove national, regional, company or market holidays.
- A calendar-day difference is not an hours-between-times calculation.
- Years and months are applied before weeks and days. Changing that order can produce a different result near month-end.
- The calculator does not determine legal filing, payment, employment or contractual deadlines. Verify the applicable rule and holiday calendar.
Frequently asked questions
Does the calculator include the ending date?
Not by default. Select “Include the end date” when both boundary dates must count.
How are leap years handled?
The calculation uses the Gregorian calendar. Years divisible by four are leap years, except century years not divisible by 400.
Why can adding one month change the day?
Months contain different numbers of days. If the original day does not exist in the target month, the calculator uses that month’s final valid date.
Are holidays removed from business days?
No. Holiday calendars vary by country, region and organization, so only Saturdays and Sundays are excluded.
Related calculators
Use the Hours Calculator for clock-time intervals and duration arithmetic, the Age Calculator for exact age and the next birthday, the Time Card Calculator for work shifts, breaks and overtime, or the Percentage Calculator for changes and proportions.