Calendar days or business days? Count the interval you mean

Decide what the dates represent

From Monday to the following Monday, seven days elapse, but eight calendar dates are touched if both Mondays are included. That is not a disagreement between calculators; it is a difference in the question being asked. Choose the rule that matches the event or plan you are describing.

KitForma’s Date Difference tool uses date-only inputs in YYYY-MM-DD format. The end must be on or after the start. It can show elapsed days or include both dates. It also describes the elapsed calendar interval in years, months and days; that decomposition is not increased by the inclusive-count choice.

Use a small example to verify the setting

Enter a one-day interval before relying on a longer result. With elapsed counting, consecutive dates produce one day; including both produces two. If the dates are equal, the corresponding counts are zero and one.

For a simple weekly example, compare 2026-09-21 with 2026-09-28. The elapsed result is seven calendar days, while the inclusive count is eight. Keep the selected rule in your notes so another person can reproduce the result instead of guessing whether the first or last date was included.

2026-09-21 → 2026-09-28
Elapsed calendar days: 7
Calendar dates including both ends: 8

Add the weekend and holiday assumptions

Business Days counts Monday through Friday and treats Saturday and Sunday as weekends. You can include both boundaries or exclude the start while including the end. A different weekend pattern or a shift-based schedule is not configurable in this tool.

No national or regional holiday calendar is downloaded. Enter the dates you want excluded, one YYYY-MM-DD date per line. Repeated holidays count once, and a holiday outside the interval or already on a weekend does not reduce the total again.

1. Choose the start, end and boundary rule.
2. Enter the relevant holiday dates from your own verified schedule.
3. Check the reported weekday-holiday exclusions as well as the final total.

Make the result reproducible

For Monday 2026-09-21 through Monday 2026-09-28, including both ends gives six weekdays. If Wednesday 2026-09-23 is a holiday in your example schedule, entering it reduces the result to five. This is an illustrative schedule, not a claim that the date is a public holiday.

If you instead exclude the starting Monday, the initial count becomes five weekdays, or four with that same example holiday. Record both the boundary rule and the holiday list when sharing the result. A bare number of business days is difficult to audit without those assumptions.

Keep date arithmetic separate from elapsed hours

KitForma treats these inputs as calendar dates using UTC boundaries so daylight-saving transitions do not change the date count. It does not calculate working shifts, partial days, overtime or an elapsed number of local clock hours. For exact moments, first establish the timestamps and time zones involved.

Add or Subtract Dates is useful for moving a date by calendar units, but adding months is not the same as adding thirty days. Review month-end behavior when that distinction matters. For contractual or official deadlines, obtain the applicable counting rule from the responsible organization; this calculator does not determine it.