How Many Days Between Two Dates? How to Count Them Correctly
Count days between dates without off-by-one errors: inclusive vs exclusive counting, leap years, business days, adding days to a date and spreadsheet formulas.
"How many days until…?" is one of the most common questions people type into a search bar. Deadlines, notice periods, pregnancies, trips, warranties and contracts all depend on getting the count right. The arithmetic is easy; the traps are in the details: whether you count the first day, how February behaves and whether weekends count. This guide covers all of them.
The basic rule: subtract the dates
The number of days between two dates is the later date minus the earlier date. From January 1, 2026 to March 1, 2026:
- January has 31 days
- February 2026 has 28 days (2026 is not a leap year)
- Total: 31 + 28 = 59 days
This is the "exclusive" count: it measures the gap between the two dates, the same way a calendar app or a spreadsheet does.
Inclusive vs. exclusive counting
This is where most errors come from. Ask yourself: does the first day count?
- Exclusive (the default): Monday to Wednesday is 2 days. Use it for "how long until", age, durations and elapsed time.
- Inclusive: Monday to Wednesday is 3 days, because you count Monday, Tuesday and Wednesday. Use it for hotel stays counted in days on site, event days, rental days and some legal or contract periods.
The rule is simple: inclusive = exclusive + 1. For example, January 1 to December 31, 2026 is 364 days apart, but the year contains 365 days if you count both ends.
When a contract or law sets a deadline, read how it defines the count. Many legal systems exclude the start day and include the last day; some extend the deadline if it falls on a weekend or holiday.
Leap years
February has 29 days in a leap year. A year is a leap year if:
- it is divisible by 4, and
- it is not divisible by 100, unless it is also divisible by 400.
So 2024 and 2028 are leap years, 1900 was not, and 2000 was. Any count that crosses a February 29 gains one day, which is why manual counts across several years often come out one or two days short.
Adding days to a date
To find a deadline, add the number of days to the start date. 90 days after March 1, 2026 is May 30, 2026:
- March 1 → March 31: 30 days
- April: 30 days (total 60)
- May 1 → May 30: 30 days (total 90)
Be careful with "3 months" versus "90 days". Three months after March 1 is June 1, which is 92 days later, not 90.
Business days (weekdays only)
If you only count Monday to Friday, the numbers change a lot. January 2026 has 31 calendar days but only 22 weekdays. To count business days you also need to remove public holidays, which vary by country and even by state or city. A good rule of thumb: there are roughly 5 business days for every 7 calendar days, minus holidays.
Spreadsheet formulas
| What you want | Excel / Google Sheets |
|---|---|
| Days between A1 and B1 | =B1-A1 |
| Inclusive count | =B1-A1+1 |
| Weekdays between two dates | =NETWORKDAYS(A1,B1) |
| Weekdays minus holidays in C1:C10 | =NETWORKDAYS(A1,B1,C1:C10) |
| Full months or years between dates | =DATEDIF(A1,B1,"m") or "y" |
| Date 90 days after A1 | =A1+90 |
Note that NETWORKDAYS counts both the start and end dates if they are weekdays, so it behaves like an inclusive count.
Years, months and days
Sometimes you need the answer as "2 years, 3 months and 12 days" instead of a total number of days. Because months have different lengths, the result depends on the method. The common method counts full years first, then full months, then the remaining days. Our date difference calculator shows both the total days and the years-months-days breakdown, so you don't have to do this by hand.
Common mistakes to avoid
- Forgetting whether the first day counts (off by one).
- Treating every month as 30 days.
- Missing a February 29 in long ranges.
- Mixing calendar days and business days.
- Ignoring time zones when the deadline has a specific time.
Frequently asked questions
How many days are there between January 1 and March 1, 2026?
59 days, because January has 31 days and February 2026 has 28.
Should I include the start date when counting days?
For durations and "days until" questions, no. Include it only when every day in the range counts, such as rental days or event days; then add 1 to the result.
How do I count only business days?
Count Monday to Friday and remove public holidays. In a spreadsheet, use NETWORKDAYS(start, end, holidays).
Is 2026 a leap year?
No. The next leap year is 2028, when February will have 29 days.
Lawyer for almost 20 years, focused on digital law, and creator of CoringaWeb. He writes the guides and builds the tools on this site.
Informational content only. For legal, financial or health decisions, consult a qualified professional.