Days Between Dates Calculator

Formula

Days between two dates

Total days = |End day serial − Start day serial|

For inclusive counting: Inclusive days = Total days + 1

A day serial represents a calendar date as a whole-day number. Using date-only values avoids daylight-saving and timezone changes that can affect local timestamps.

Add or subtract calendar days

Result date = Start date ± Number of calendar days

The selected operation determines whether the calculator moves forward from the start date (Add) or backward from it (Subtract).

Weekdays-only counting

Starting from the selected date, move forward or backward one calendar day at a time. Count Monday through Friday and skip Saturday and Sunday. Holidays are not excluded.

No rounding is used. Day totals are calculated as whole calendar days.

Variable definitions

• Start date: The earlier calendar date in the interval, or the reference date for Add / Subtract mode.
• End date: The later calendar date in the interval for Days Between mode.
• Day serial: A whole-day number representing a calendar date, used for date-only arithmetic.
• Include end date: When on, adds one day so both boundary dates are counted.
• Operation: In Add / Subtract mode, whether to move forward (Add) or backward (Subtract) from the start date.
• Number of days: A whole non-negative number of days to add or subtract.
• Skip Saturday and Sunday: When on, only Monday through Friday are counted while moving to the result date.

Step-by-step calculation

1. Read the start date and end date as calendar dates without time-of-day values.
2. Convert both dates to whole-day calendar values (day serials).
3. Subtract the earlier value from the later value.
4. Use the absolute difference so reversed dates still produce a positive span.
5. Add one day only when Include end date is selected.
6. Divide the total by 7 to show full weeks and remaining days.
7. When the weekday and weekend breakdown is enabled, count Monday through Friday separately from Saturday and Sunday.

Worked example

Start date: January 10, 2026. End date: June 22, 2026. End date excluded.

• Total days: 163
• Weeks: 23 weeks, 2 days (163 = 23 × 7 + 2)
• Calendar duration: 5 months, 12 days
• Weekdays: 115
• Weekend days: 48 (115 + 48 = 163)
• Start day: Saturday. End day: Monday.

Turning on Include end date changes the total to 164 days.

How to use this calculator

Choose Days Between to compare two dates.

• Enter the start and end dates.
• Use the Today shortcuts when useful.
• Use Swap dates to exchange the entered dates.
• Turn on Include end date when both boundary dates should count.
• Turn the weekday and weekend breakdown on or off as needed.

Choose Add / Subtract Days to find a future or past date.

• Select Add or Subtract.
• Enter a positive whole number of days.
• Optionally skip Saturday and Sunday.

Use Copy result to copy the current result, Share to share it, and Reset to restore the calculator's default dates and options.

Common mistakes

• Confusing inclusive and exclusive counting. By default the end date is excluded; turn on Include end date when both boundaries should count.
• Assuming every month has 30 days. Calendar arithmetic uses actual month lengths and leap years.
• Using local timestamp differences for date-only calculations. Local midnights change with daylight-saving; this calculator uses date-only day serials.
• Calling every Monday-to-Friday date a holiday-adjusted business day. Holidays are not excluded here.
• Entering a negative number. The Add or Subtract control already determines direction; use a positive whole number.
• Confusing total days with the Y/M/D breakdown. 163 total days and 5 months, 12 days are two ways to describe the same interval.

What the calculator results mean

• Total days: the number of calendar days in the selected interval.
• Weeks: full 7-day weeks plus any leftover days.
• Calendar duration: the span expressed as whole calendar years, months, and remaining days.
• Weekdays: Monday through Friday dates in the selected interval.
• Weekend days: Saturday and Sunday dates in the selected interval.
• Start day and end day: the day of the week for each selected date.
• Counting method: whether the end date was excluded or included.

For Add / Subtract Days mode:

• Result date: the calendar date after applying the operation.
• Day of the week: the weekday of the result date.
• Operation: Add or Subtract.
• Days applied: the whole number you entered.
• Calendar days vs weekdays-only: weekdays-only counting skips Saturday and Sunday.

Inclusive vs. exclusive date counting

By default, the calculator includes the earlier date and excludes the later date. Turn on Include end date when both boundary dates should count. Monday to the following Monday is 7 days with the end date excluded and 8 days when the end date is included. The same date to itself is 0 days by default and 1 day when the end date is included.

How weekdays and weekends are counted

Weekdays are Monday through Friday. Weekend days are Saturday and Sunday. Holidays are not automatically excluded, so the weekday total is a simple Monday-to-Friday count.

Calendar years, months, and days

Calendar duration uses actual calendar boundaries instead of fixed 30-day months or 365-day years. The calculator counts whole years first, then whole months, then remaining days. When a date does not exist in the target month, the calculation uses the last valid day of that month.

Add or subtract days example

Start date: Monday, July 6, 2026. Operation: Add. Days: 5. With weekdays-only counting the result is Monday, July 13, 2026 because Saturday and Sunday are skipped, so five weekdays end on the following Monday. With normal calendar-day counting, five days after July 6, 2026 is Saturday, July 11, 2026.

Frequently asked questions