Date Difference Calculator

How the days between two dates are counted

The difference between two dates is the number of midnights you pass going from one to the other. From Monday to Wednesday is 2 days. If you want to count both the first and the last day, as for a 3-day festival from Monday to Wednesday, choose the inclusive option, which adds one.

Days = end date − start date
Inclusive days = end date − start date + 1

Worked example

From 1 January 2026 to 25 December 2026:

• Difference: 358 days, which is 51 weeks and 1 day.
• Working days (Monday to Friday) from the start date up to, but not including, the end date: 256. Counting 25 December as well (a Friday) gives 257.

Public holidays are not subtracted automatically because they differ by country and region. Subtract your local holidays from the working-day figure.

Months and years are not fixed lengths

Days and weeks are exact. Months vary from 28 to 31 days and years from 365 to 366, so "how many months between two dates" depends on the dates themselves. The calculator counts completed calendar months, the same way as the age calculator, and then the remaining days.

Practical uses

• Deadlines and notice periods: "30 days from receipt" usually means calendar days unless the contract says working days.
• Project planning: working days tell you how much time a team actually has.
• Travel: hotel stays are counted in nights (the plain difference), while trips are often described in days (inclusive).
• Pregnancy, warranties, subscriptions: many periods are defined in days or weeks from a start date.
• Interest calculations: some loans charge interest per day between payment dates.

Day-count conventions in finance

Banks do not always count days the same way. "Actual/365" uses the real number of days, while "30/360" treats every month as 30 days and the year as 360 days, which simplifies bond calculations. If you are checking interest on a statement, ask which convention the lender uses.

Common mistakes

• Off-by-one errors: decide whether both the start and end dates count before you start.
• Ignoring weekends: 10 working days is two full weeks, not ten calendar days.
• Forgetting leap years: 2028 has a 29 February, which adds a day to any range that crosses it.

Days in each month

The knuckle trick helps: count the months over your knuckles and the gaps between them; knuckle months have 31 days.

Leap years

A year is a leap year if it is divisible by 4, except century years, which must also be divisible by 400. So 2028 is a leap year, 2100 is not, and 2000 was. Any range that includes 29 February gains a day.

Counting working days by hand

Count the full weeks in the range and multiply by 5, then add the weekdays in the leftover days. 358 days is 51 full weeks (255 working days) plus 1 extra day; from 1 January 2026, a Thursday, that leftover day is a weekday, which gives the 256 working days shown in the example above. Then subtract public holidays that fall on weekdays.

Turning a day count into weeks and years

Divide by 7 for weeks and keep the remainder as days: 100 days is 14 weeks and 2 days. For years, divide by 365.2425, the average length of a Gregorian year including leap days, so 1,000 days is about 2.74 years. Months are the awkward unit, because they run from 28 to 31 days; that is why the calculator also shows a calendar breakdown in years, months and days instead of dividing by a fixed 30. For countdowns such as "days until a holiday", enter today as the start date; the result updates correctly across month ends and leap years without any manual counting.

Frequently asked questions

Sources

• ISO 8601: date and time representation (Gregorian calendar, weeks starting on Monday).
• International Swaps and Derivatives Association (ISDA) definitions of day-count fractions (Actual/365, 30/360).

Last reviewed 5 October 2026. Results are estimates; see our disclaimer.