date-time calculator
Date Difference Calculator
Calculate calendar duration, elapsed or inclusive days, weekdays, and dates before or after a day offset.
UTC date-only
Calculate date differences
Result
Enter dates and choose Calculate.
Formula version 1.0.0 · Business days exclude weekends, not holidays.
Counting conventions
How date differences are counted
Standard elapsed days exclude the start date. Select inclusive counting to include both endpoints.
Calendar duration
Complete years are counted first, then complete constrained months, then remaining days.
Weekdays
Business-day mode excludes Saturday and Sunday. It does not know public, religious, company, or regional holidays.
Add or subtract days
Day shifts use UTC date-only arithmetic, so daylight-saving clock changes cannot add or remove a day.
Month ends
Calendar-month calculations clamp to the final valid day when a corresponding date does not exist.
How to use this calculator
- Choose Difference between dates, Weekdays between dates, Add days to a date, or Subtract days from a date.
- Enter Start date and the displayed End date or Number of days field.
- For Difference between dates, choose whether to include both endpoints.
- Select Calculate, then review the day result, calendar breakdown, and counting rules.
Symbols and units
| Symbol | Meaning | Unit or domain |
|---|---|---|
startDate | Starting Gregorian calendar date | YYYY-MM-DD date only |
endDate | Ending Gregorian calendar date | YYYY-MM-DD date only |
amount | Whole-day offset added to or subtracted from the start | Nonnegative whole days |
inclusive | Counts both start and end dates when enabled | Boolean counting convention |
business days | Monday through Friday in the entered span | Days; holidays not excluded |
Checked examples
Elapsed versus inclusive days
Inputs: Start date: 2024-01-01; End date: 2024-01-03
Calculation: Elapsed: Jan 3 − Jan 1 = 2 days. Inclusive: 2 + 1 endpoint day.
Result: 2 elapsed days or 3 inclusive days
Inclusive counting adds one when both endpoints are counted.
Check: date-difference.test.ts — supports exclusive and inclusive differences
Count weekdays without holidays
Inputs: Mode: Weekdays between dates; Start: 2024-01-01; End: 2024-01-08
Calculation: Count Monday–Friday while excluding Saturday and Sunday.
Result: 5 weekdays
Public, religious, company, and regional holidays are not known to this model.
Check: date-difference.test.ts — counts business days excluding weekends
Assumptions, rounding, and limits
- Dates use the proleptic Gregorian calendar and UTC date-only arithmetic.
- The end date must be on or after the start date for difference modes.
- Elapsed counting excludes the start date; inclusive counting includes both endpoints.
- Business-day mode excludes Saturday and Sunday only and does not exclude holidays.
- Add/subtract amounts must be nonnegative whole days within the supported date range.
- Calendar duration counts complete constrained years, then months, then remaining days; month ends clamp when necessary.
Frequently asked questions
Does business-day mode exclude public holidays?
No. It excludes Saturdays and Sundays only because holiday calendars vary by country, region, company, and year.
What is inclusive counting?
It includes both the start and end dates. Standard elapsed-day counting excludes the start date.
Can daylight-saving changes alter the answer?
No. The calculator uses date-only UTC arithmetic and does not calculate clock-hour durations.
Sources and review
- TC39: Temporal.PlainDate — Date-only differences, addition, subtraction, and constrained calendar operations
- Microsoft: WorksheetFunction.NetworkDays — Documented weekday-counting convention
- Internet Engineering Task Force: Date and Time on the Internet: Timestamps — Gregorian date syntax and leap-year definition
- Formula version
- date.difference@1.0.0
- Formula review
- Equatara formula review
- Editorial review
- Equatara editorial review
- Last verified
- 2026-10-25
- Applicability
- Global educational date-only arithmetic; weekday mode excludes weekends but not holidays.
- Next review
- On material formula/source change, or by 2028-10-25.
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Found a problem?
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