About the Number of Days Calculator
This tool counts the exact number of calendar days between a start date and an end date. It uses one formula — subtract the earlier date from the later one — and offers the one variable that trips people up in real life: whether the end date itself should be counted.
The formula
Every date can be converted to a single point on a timeline (its distance in days from a fixed reference point). The number of days between two dates is simply:
- Exclusive count (default): Days = End date − Start date. This is how nights in a hotel, or the "duration" between two moments, are usually measured. January 1 to January 5 is 4 days.
- Inclusive count: Days = (End date − Start date) + 1. This counts both the start and end calendar dates, the way vacation days, billing days, or "how many days was I sick" are often measured. January 1 to January 5 inclusive is 5 days.
From the total day count, this calculator also derives a weeks-and-days breakdown (divide by 7, keep the remainder), and it walks every calendar date from the start date through the end date — inclusive of both — to tally how many fall on a weekday (Monday through Friday) versus a weekend day (Saturday or Sunday).
Picking inclusive vs. exclusive
Get this wrong and you're off by exactly one day — a classic "fencepost" error. A simple test: if you're measuring a gap or a duration between two instants (checkout minus check-in, delivery date minus order date), use exclusive counting. If you're counting how many calendar days a thing occupies, including the first and last one (a multi-day event, a rental period billed by the day, a course that runs "day 1 through day 5"), use inclusive counting.
Where day counts like this show up
- Contract and legal deadlines written as "within 30 days of signing" or "10 business days' notice"
- Prorating rent, subscriptions, or insurance premiums for a partial billing period
- Loan and interest calculations that use an actual-day-count convention
- Project timelines, sprint lengths, and countdowns to a launch or event date
- Return, warranty, and waiting-period windows measured in calendar or business days
Business days and holidays
The weekday/weekend split here follows the standard Monday-through-Friday definition of a business day. It does not subtract public holidays, because holiday calendars vary by country, region, and even by employer. If your use case needs a holiday-aware count (for example, a legal filing deadline), start from the weekday figure this calculator gives you and subtract any holidays that fall within your date range.