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Days Between Dates
Find the difference between two dates quickly.
Calculating Days Between Dates
Date calculations are used for project deadlines, contract durations, subscription lengths, and legal compliance (notice periods, statute of limitations). The math involves accounting for leap years, different month lengths, and business day exclusions.
Calendar Facts for Date Calculations
- A standard year = 365 days; a leap year = 366 days
- Average Gregorian month = 30.44 days (365/12)
- Business days exclude weekends = typically 261 working days per year in the US
- Federal holidays (US) = 11 days per year — reduce business day counts for contract purposes
Common Date Range Uses
- Contract notice period: "30 days written notice" — count exact calendar days from delivery date
- Subscription billing: monthly billing = same date next month
- Project planning: working days between start and deadline (excluding weekends)
How do I calculate business days in Excel?
In Excel: use NETWORKDAYS(start_date, end_date) — it automatically excludes weekends and optionally a list of holidays. In JavaScript: the date-fns library provides differenceInBusinessDays() for clean business-day calculations without manual loops.
How many days until a specific holiday or event?
Use the date difference calculator by setting today as the start date and your target event date as the end date. For recurring annual events, check whether the current year's date has passed — if so, use next year's date instead for the countdown.