How to Calculate Days Between Dates
6 min read · Updated September 26, 2026 · by the SolveCalcPro editorial team
Counting days between dates looks easy until months of different length and leap years get involved. This guide shows a reliable by-hand method and how business days differ.
The method
- If both dates are in the same year, convert each to its day-of-year number (1 January = 1; 31 December = 365 or 366).
- Subtract the earlier from the later.
- For different years, add the full years in between (365 each, 366 for leap years).
Worked example
From 1 January to 12 March 2026: January has 31 days and February 28 (2026 is not a leap year), so 12 March is day 31 + 28 + 12 = 71. Subtracting day 1 gives 70 days.
Leap years
A year is a leap year if divisible by 4, except century years not divisible by 400. 2024 had 366 days; 1900 had 365; 2000 had 366.
Business days
Business days exclude weekends (and holidays you list). 1 to 31 March 2026 contains 22 weekdays. Use the days between dates, business days and birthday countdown tools to check your own.
Practice questions
Test yourself, then tap to check. Answers are calculated by the tools linked below.
- How many days are between 25 November 2026 and 25 December 2026?
Show answer
Total days: 30
- How many business days are in November 2026, excluding Thanksgiving (26 November)?
Show answer
Business days: 20
- Someone was born on 20 August 2010. Counting from 1 October 2026, how many days until their next birthday, and what age does it turn?
Show answer
Next birthday: Friday, August 20, 2027 · Days remaining: 323
Frequently asked questions
How do I count the days between two dates?
Convert both to day-of-year (or a running day count) and subtract, adding 365 or 366 per whole year between.
Is the end date included?
By default the span excludes the start day and counts the end day; add one if both ends count.
How are business days counted?
Count weekdays only, then subtract public holidays.
How do leap years affect the count?
A leap year adds 29 February, so spans that include it are a day longer.
Try it yourself
Days Between Dates CalculatorFind the exact number of days, weeks and business days between any two dates.Business Days CalculatorCount working days between two dates, or add working days to a date, excluding weekends and holidays.Birthday Countdown CalculatorSee exactly how many days until the next birthday, and what age it turns.Date Calculator (Add or Subtract Days)Add or subtract days, weeks, months and years from any date.Keep learning
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