Days between dates
Two dates in, both counts out: the plain difference and the inclusive count. No single hidden convention — the number you need depends on why you are counting.
Which count should you use?
Exclusive count (simple subtraction)
The number of whole days in between. "10 working days from now" and "90 days from today" both use this logic: today is the anchor, not day 1.
Inclusive count (add 1)
Counts both endpoints. Use this for "days covered" questions: hotel nights, day-count interest in some jurisdictions, attendance periods.
When a policy is ambiguous
Assume the convention that hurts you (the earlier deadline) and verify with whoever wrote the policy. Return windows, in particular, have no industry standard.
Common questions
Do you count the start or end date?
We show both. The exclusive count (simple subtraction) is what most people mean by "days between"; the inclusive count adds both endpoints, which is what you want for "how many days inclusive of both dates". Contracts rarely say which they mean — that ambiguity is exactly why both numbers are on screen.
How are days between dates calculated across a leap year?
By real calendar arithmetic, with the full leap-year rule (including the year 2100 exception). February 29 counts as a day when it is inside your range.
Why do different calculators give different results for ancient dates?
Three conventions coexist: the Julian calendar (used before each country's switch), the proleptic Gregorian (extend modern rules backward), and astronomical year numbering (which has a year 0; civil BC/AD does not). We use the proleptic Gregorian calendar and label it — for dates after October 1582 in most of Europe, or after 1752 in Britain and its colonies, this matches the historical record.
Last updated 2026-11-04 · Calculations follow the full leap-year rule (including the year 2100 exception).