Formula
days = UTC calendar day(end) − UTC calendar day(start)
Map each valid calendar date to an integer UTC-style day index, subtract the indexes, then apply inclusive and sign choices.
Date & time
● Runs locallyDays Between Dates
Count calendar days between two dates without converting local midnights into time-zone-sensitive timestamps. Choose exclusive or inclusive counting and keep or remove direction with the signed option.
Example values
Calendar-day difference
Assumptions
- The Gregorian calendar is used from year 0001 through 9999.
- Inclusive mode counts both endpoints for a non-zero span.
Dates represent calendar labels, not instants. Daylight-saving changes cannot alter the result.
Formula review
Formula v1.0.0
Reviewed 2026-08-03
CalcFlow engineering review
Days Between Dates: Worked example
The day index for 20 August 2026 is 17 greater than for 3 August. Exclusive counting gives 17 days; inclusive counting gives 18.
Frequently asked questions
What is exclusive counting?
It measures how many day boundaries separate the two dates. Inclusive mode additionally counts both endpoint dates.
Can daylight saving change the answer?
No. The engine uses date-only integer arithmetic rather than local timestamps.
What does signed mode do?
It returns a negative count when the end date is before the start date.