Do you include the start and end dates when counting?

It depends on the context. 'Days between' typically excludes both endpoints (January 1 to January 3 = 2 days). 'Days from' usually includes the start date. Legal and contractual calculations may include or exclude endpoints — always check the specific terms.

UtilityApril 12, 2026

How to Count Days Between Two Dates

Q: How do you count days between two dates?

Subtract the earlier date from the later date. For dates in the same month, subtract the day numbers. For dates across months, add the remaining days in the start month, all days in full months between, and the day number in the end month. Or use a calculator for instant results.

Q: What is the difference between calendar days and business days?

Calendar days include every day — weekends and holidays. Business days (or working days) exclude weekends (Saturday and Sunday) and typically exclude federal/public holidays. 30 calendar days equals roughly 22 business days.

Q: How many days are in each month?

January 31, February 28 (29 in leap years), March 31, April 30, May 31, June 30, July 31, August 31, September 30, October 31, November 30, December 31. The mnemonic 'Thirty days hath September, April, June, and November' covers the 30-day months.

Q: How do leap years affect day counting?

Leap years add one day (February 29). A year is a leap year if divisible by 4, except century years must be divisible by 400. So 2024 is a leap year, 1900 was not, and 2000 was. When counting across February in a leap year, add 29 days instead of 28.

By The hakaru Team·Last updated March 2026

Quick Answer

Subtract the start date from the end date to get the number of days between them. January 15 to March 10 = 16 remaining days in January + 28 days in February + 10 days in March = 54 days. For business days, subtract weekends and holidays.

Try the Days Between Dates Calculator →

The Manual Calculation Method

Counting days between dates by hand requires knowing how many days are in each month. Here's the process:

Same month:Subtract the day numbers. March 5 to March 22 = 22 − 5 = 17 days.

Different months: Count the remaining days in the start month, add the full days of any months in between, then add the day number of the end month.

Example: April 20 to July 8. Remaining days in April: 30 − 20 = 10. Full months: May (31) + June (30) = 61. Days in July: 8. Total: 10 + 61 + 8 = 79 days.

Days in Each Month

Month	Days	Month	Days
January	31	July	31
February	28/29	August	31
March	31	September	30
April	30	October	31
May	31	November	30
June	30	December	31

The knuckle trick works: make two fists and count across the knuckles and valleys. Knuckles (high) = 31 days, valleys (low) = 30 days (except February). Starting from the left pinky knuckle: January (31), valley (Feb 28/29), March (31), valley (April 30), May (31), valley (June 30), July (31). Then start over on the same hand: August (31), valley (Sept 30), October (31), valley (Nov 30), December (31).

Calendar Days vs. Business Days

This distinction matters for legal deadlines, shipping estimates, project timelines, and payment terms. “Net 30” on an invoice typically means 30 calendar days, not business days. But “5 business days for processing” excludes weekends.

Calendar Days	Approximate Business Days
7	5
14	10
30	22
60	43
90	65
365	261

The average month has about 22 business days. The average year has 261 business days (365 minus 104 weekend days). Federal holidays reduce this by 11 days in the U.S., bringing the typical working year to 250 days.

The Inclusive vs. Exclusive Counting Problem

“How many days from Monday to Friday?” Is it 4 or 5? That depends on whether you include the start day, the end day, or both.

Exclusive (days between): Monday to Friday = 4 days. This is the mathematical difference and the most common interpretation.

Inclusive (days from ... through): Monday through Friday = 5 days. This counts both endpoints.

Legal and contractual language is often ambiguous. “Within 30 days of the agreement date” — does day 1 start on the agreement date or the day after? Courts have split on this, which is why precise contracts specify “within 30 calendar days following the execution date, with the first day being the day after execution.”

Leap Year Rules

A year is a leap year if it's divisible by 4. But century years (1800, 1900, 2100) are not leap years unless they're also divisible by 400. So 2000 was a leap year, but 1900 was not. The next exception is 2100.

When counting days between dates that span February, you need to check if it's a leap year. February has 29 days in a leap year instead of 28. Getting this wrong in a multi-month calculation throws off your count by one day.

Common Use Cases

Project deadlines.“The report is due in 45 days” — count 45 calendar days from today to find the due date.

Pregnancy due dates. Estimated due date is typically 280 days (40 weeks) from the first day of the last menstrual period.

Lease and contract terms.“30-day notice required” means you need to notify at least 30 days before the intended end date.

Shipping estimates.“Ships in 5–7 business days” excludes weekends and holidays, so 5 business days from a Monday order is the following Monday.

Event planning.“How many days until the wedding?” is a simple subtraction from today's date, but it helps to also know the number of weekends (for planning tasks) and business days (for vendor coordination).

Use the days between dates calculator to instantly find the exact number of days, weeks, and business days between any two dates.

Frequently Asked Questions

How do you count days between two dates?+

Subtract the earlier date from the later date. For same-month dates, subtract the day numbers. For different months, add remaining days in the start month, full days of months in between, and the day number of the end month.

Do you include the start and end dates?+

“Days between” typically excludes both endpoints. “Days from ... through” includes both. Legal contexts vary, so always check the specific terms.

What is the difference between calendar days and business days?+

Calendar days include every day. Business days exclude weekends and usually federal holidays. 30 calendar days equals roughly 22 business days.

How many days are in each month?+

Jan 31, Feb 28/29, Mar 31, Apr 30, May 31, Jun 30, Jul 31, Aug 31, Sep 30, Oct 31, Nov 30, Dec 31. February has 29 days in leap years.

How do leap years affect day counting?+

Leap years add February 29. A year is a leap year if divisible by 4, except century years must also be divisible by 400. When counting across February in a leap year, use 29 days instead of 28.