How to Calculate Days Between Two Dates: Calendar Days, Business Days & Excel

How many days until a deadline? How long did a project last? How many working days are left this month? Counting days sounds simple, but months of different lengths, leap years, weekends and holidays make it easy to be off by one. This guide explains how to calculate days between two dates by hand and in Excel, when to include the end date, how to count business days, and how to add days to a date – with worked examples.

How to Calculate Days Between Two Dates

The quickest manual method is to count the days left in the start month, add the full months in between, and add the days in the end month:

1. Days remaining in the start month (after the start date).
2. Days in each full month in between – remember 30 days for April, June, September and November, 28 for February (29 in a leap year), and 31 for the rest.
3. Days in the end month up to the end date.

Worked example

How many days from 15 March 2026 to 10 June 2026?

• March: 31 − 15 = 16 days
• April: 30 days
• May: 31 days
• June: 10 days
• Total: 16 + 30 + 31 + 10 = 87 days

The Days Between Dates Formula

Computers and spreadsheets turn each date into a serial number (a day count from a fixed starting point) and subtract:

Days = End date − Start date

This gives the number of days from the start date to the end date, not counting the start day itself. From 1 January 2026 to 31 December 2026 is 364 days.

Should You Include the End Date?

Whether to include the end date depends on the question you are asking:

Getting this wrong by one day is the most common date calculation mistake – always check which one your rule or contract uses.

Leap Years

A leap year has 366 days, with 29 February. A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. So 2024 and 2028 are leap years, 2026 and 2027 are not, and 2100 will not be. When a date range includes 29 February of a leap year, it contains one extra day – from 1 February to 1 March is 29 days in 2028 but 28 days in 2026.

How to Calculate Business Days

Business days (working days) are usually Monday to Friday, excluding public holidays. To count them:

1. Count the full weeks in the range and multiply by 5.
2. Add the weekdays in the leftover days.
3. Subtract any public holidays that fall on a weekday.

A year has 260 or 261 weekdays; 2026 has 261. After public holidays, the UK (England and Wales, 8 bank holidays) has about 253 working days in 2026 and the US (11 federal holidays) about 250. Business-day counts matter for bank transfers, delivery estimates, notice periods, refunds and legal deadlines.

How to Add or Subtract Days from a Date

To find the date 90 days after 1 October 2026, count forward: 31 days take you to 1 November, 30 more to 1 December, 29 more to 30 December – that is 30 December 2026. Adding business days is harder because you skip weekends and holidays, which is where a days calculator or the date calculator saves time. To add months or years (for example, 6 months from today), use the date calculator, which handles month-end dates correctly.

Days Between Dates in Excel and Google Sheets

• Calendar days: =B2-A2 (format the result cell as a number).
• Including the end date: =B2-A2+1
• Days from today: =A2-TODAY()
• Business days (Mon–Fri, including both ends): =NETWORKDAYS(A2,B2,holidays)
• Custom weekends, e.g. Sunday only: =NETWORKDAYS.INTL(A2,B2,11,holidays)
• Add business days: =WORKDAY(A2,10,holidays)

Note that NETWORKDAYS counts both the start and end dates if they are working days.

Everyday Uses of Day Counting

• Work: notice periods, probation, leave balances and project timelines. Our notice period calculator finds your last working day.
• Money: invoice due dates such as net 30, loan interest periods and FD tenures.
• Travel: visa validity, passport rules and the Schengen 90/180-day limit.
• Health: pregnancy weeks, medicine courses and days since quitting smoking.
• Personal: countdowns to birthdays, weddings and exams, or your age in days with the age calculator.

Days in Each Month

A handy trick: make fists and count months across your knuckles – knuckles are 31-day months and the dips between them are the shorter months.

Common Mistakes

• Forgetting to decide whether the end date is included.
• Assuming every month has 30 days.
• Missing 29 February in a leap year.
• Counting weekends in a "business days" deadline, or holidays that fall on a weekend.
• Reading dates in the wrong format – 03/04 is 3 April in India and the UK but 4 March in the US.

Counting Days for Special Situations

Days until an event

For a countdown, subtract today's date from the event date and do not include the end date. Our days calculator also shows a live countdown in days, hours, minutes and seconds.

Age in days

Subtract your date of birth from today. Someone born on 1 January 2000 is 9,769 days old on 30 September 2026.

Loan and deposit interest

Banks count the exact number of days for interest on short-term deposits and many loans, usually on a 365-day year. A deposit from 1 April to 30 September earns interest for 182 days.

Time Zones and Day Counts

When dates are in different time zones – such as a flight or an international deadline – the calendar date may differ depending on where you are. Always use the time zone stated in the rule or contract. For hour-level calculations, such as working out a flight's arrival time, use our time calculator.

Worked Example: Business Days in October 2026

October 2026 has 31 days. It starts on a Thursday, so it contains 22 weekdays (Monday to Friday) and 9 weekend days. If a public holiday falls on a weekday during the month, subtract it to get the number of working days. For example, with Gandhi Jayanti on Friday 2 October as a holiday, there are 21 working days in October 2026.

Frequently Asked Questions

Note: Working-day figures use England and Wales bank holidays and US federal holidays for 2026. Your employer or local holidays may differ.