How to Calculate Days Between Dates (Inclusive or Not)

To calculate the days between two dates, subtract the earlier date from the later one. That counts the start date but not the end date, so from Friday, October 2, 2026 to Christmas, Friday, December 25, 2026 is 84 days. If you need to count both the first and the last day, add 1: 85 days.

That one decision, whether to count the end date, causes most of the disagreements between people, calculators and spreadsheets. This guide explains when to count inclusively and when not to, shows a reliable way to do it by hand using month lengths, works through checked examples, and covers business days and the Excel formulas. For an instant answer, the date duration calculator does all of it, with an option to include the end date.

Inclusive vs exclusive counting

Subtracting dates gives an exclusive count: the number of midnights you pass, or the number of “sleeps”. January 1 to January 2 is 1 day. An inclusive count counts every calendar day you touch, so January 1 to January 2 is 2 days. Neither is wrong; they answer different questions.

If a contract, notice period or legal deadline is involved, the counting rule is set by the document or the law that applies, not by the calculator. Read how it defines “days” (calendar days or business days) and whether the first day counts, and if it’s unclear, ask.

How to calculate days between dates by hand

The reliable manual method has three parts:

1. Days left in the start month: the month’s length minus the start day.
2. Full months in between: add their lengths.
3. Days into the end month: the end day itself.

For October 2 to December 25, 2026: October has 31 days, so 31 − 2 = 29 days remain. November is a full month of 30 days. Then 25 days of December. 29 + 30 + 25 = 84 days, which matches the subtraction. Add 1 if you want the inclusive count.

If both dates are in the same month, just subtract the day numbers. If they’re years apart, count whole years first (365 days each, 366 for any that contain a February 29), then the leftover months and days.

Month lengths

February is the usual trap. February 1 to March 1 is 28 days in 2027 but 29 days in 2028, because 2028 is a leap year. Any range that crosses the end of February in a leap year is one day longer; our leap year guide lists the next ones.

Worked examples

• The whole of 2026: January 1 to December 31, 2026 is 364 days by subtraction, or 365 counting both ends, which is the number of days in the year.
• Four years: February 29, 2024 to February 29, 2028 is 1,461 days, or 208 weeks and 5 days.
• A birthday count: someone born on July 20, 1990 has been alive 13,223 days on October 2, 2026: 36 years, 2 months and 12 days.
• A long countdown: October 2, 2026 to Diwali on October 29, 2027 is 392 days, exactly 56 weeks.
• Counting forward: 84 days after October 2, 2026 is Friday, December 25, 2026. Going forward and going back are the same calculation in reverse, which the date calculator does for any number of days, weeks or months.

Counting business days

Business days are Monday to Friday, usually minus public holidays. Two tools can disagree by one here too, depending on whether both ends count.

• Our calculators count the weekdays after the start date, up to and including the end date. From October 2 to December 25, 2026 that’s 60 weekdays, or 56 after Columbus Day, Veterans Day, Thanksgiving and Christmas.
• Excel’s NETWORKDAYS counts both the start and end date, so for the same range it returns 61, or 57 with those four holidays in its holiday list. The difference is October 2 itself, a Friday.

For deadlines like “within 10 business days”, use the business days calculator, which steps forward from today and can skip US federal holidays.

Days between dates in Excel

Excel stores dates as serial numbers (January 1, 1900 is 1), so date math is ordinary arithmetic. With the start date in A1 and the end date in B1:

• =B1-A1 gives the exclusive count. Format the cell as a number, not a date.
• =DAYS(B1,A1) does the same; note that the end date comes first. Microsoft’s example, =DAYS("15-MAR-2021","1-FEB-2021"), returns 42.
• =B1-A1+1 gives the inclusive count.
• =DATEDIF(A1,B1,"Y"), "YM" and "MD" give the years, the leftover months and the leftover days. For July 20, 1990 to October 2, 2026 they return 36, 2 and 12.

Microsoft warns on its DATEDIF page that the “MD” unit has known limitations and can return a negative number, a zero or an inaccurate result, so check it against another method. Our guide to Excel date formulas covers adding days, months and workdays.

Frequently asked questions

How do I calculate the number of days between two dates?

Subtract the earlier date from the later one. That counts the start date but not the end date. Add 1 if you need to count both days.

Does “days between” include the end date?

Usually not. Calculators and spreadsheet subtraction give the exclusive count, so January 1 to January 2 is 1 day. Our date duration calculator has an option to include the end date.

How many days until Christmas 2026?

From Friday, October 2, 2026, Christmas on Friday, December 25, 2026 is 84 days away, exactly 12 weeks. The Christmas countdown updates daily.

How many days are in a year?

365 in a common year and 366 in a leap year. 2026 and 2027 have 365 days; 2028 has 366.

Why do two calculators give different answers?

Usually because one counts the end date and the other doesn’t, or because one counts business days with holidays and the other without. Check both settings before you rely on the result.