Counting the days, weeks, or months between two dates sounds simple — until you factor in leap years, variable month lengths, and the difference between calendar and business days. This free date difference calculator handles all the edge cases instantly. Whether you're planning a project deadline, counting down to an event, or verifying a contract period, you'll get an exact breakdown in seconds.
How the Date Difference Calculator Works
The calculator converts both dates to milliseconds since the Unix epoch, subtracts them, then converts the result back into days, weeks, months, years, and hours. For business days, it iterates through every day in the range and excludes Saturdays and Sundays. Months are approximated at 30.4375 days and years at 365.25 days to account for leap year distribution. The result shown is always the absolute difference, with a direction indicator (before/after) in the summary.
3 Real-World Examples
Wedding on October 15, 2026, today is May 3, 2026 → 165 days (or 23 weeks, 4 days). Track key milestones: venue booking deadline (6 months), invitations (3 months), final fitting (2 weeks).
Sprint starts May 5, deadline June 13. That's 39 calendar days but only 28 business days. If your team works 5 days/week, that's just under 6 working weeks — plan accordingly.
Born June 22, 1990. Today is May 3, 2026 → 35 years, 10 months, 11 days. Legal contexts (insurance, contracts) often need exact age in days or months — not just the year.
Tips
- Use the "Set Today" button to lock the start date to the current date, then change only the end date for a quick countdown.
- For legal deadlines, always use business days — a "30-day notice" in a contract typically means 30 calendar days, but double-check the wording.
- To count inclusive days (start date + end date both counted), add 1 to the result — useful for booking durations like hotel nights.
- Negative differences (end date before start date) still work — the calculator returns the absolute difference with a directional label.
Understanding Calendar vs. Business Days
Calendar days count every day of the week — 365 per year (366 in a leap year). Business days exclude Saturdays and Sundays, giving approximately 260 working days per year. For a 30-day calendar period, you typically have 22 business days. This distinction matters enormously for contracts, service-level agreements, project sprints, and government processing times. Federal and public holidays add another layer — they vary by country and employer, and are not excluded by default in this calculator.