Date Difference
Calculate days, weeks, and business days between any two dates.
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When to use this
Your lease ends on August 14 and you need to know exactly how many days you have to find a new place. A contract specifies "delivery within 90 business days" and you need to pin down the actual calendar date. You're planning a trip and want to know if 17 days is enough to do everything you have in mind. Date math sounds trivial until you try to account for months with different lengths, leap years, and weekends.
Project managers use this constantly — estimating sprints, calculating buffer time, and converting between calendar days and business days. HR departments need it for probation periods, benefits eligibility dates, and FMLA calculations. Real estate closings, legal filing deadlines, and insurance waiting periods all hinge on precise day counts.
It's also the quick answer to casual questions: how many days until Christmas, how long until summer break, or how many weekends are left before a deadline. The business-day count is especially useful because manually counting while skipping Saturdays and Sundays is tedious and error-prone.
Good to know
Business days and calendar days diverge fast. A 30-calendar-day window contains only about 22 business days. Over 90 calendar days, you lose roughly 26 days to weekends. If a deadline is in "business days," always convert to calendar days so you don't underestimate the timeline.
This calculator does not account for public holidays. Business days here means weekdays (Monday–Friday). Federal holidays, state holidays, and company-specific closures aren't subtracted because they vary by location and employer. For precise SLA or legal deadline calculations, subtract holidays manually from the business day count.
"Inclusive" vs. "exclusive" counting matters. If an event starts on January 1 and ends on January 31, is that 30 days or 31? It depends on whether you count the start date. This calculator uses exclusive counting (the standard for durations) — January 1 to January 31 = 30 days. Legal and medical contexts sometimes use inclusive counting, so verify which convention applies.
Months are not equal units. "Three months from January 31" could be April 30 or May 1 depending on interpretation, because February has fewer days. This calculator handles month math by adjusting to the last valid day of the target month when needed.
Quick Reference
| Duration | Calendar Days | Business Days (approx.) |
|---|---|---|
| 1 week | 7 | 5 |
| 2 weeks | 14 | 10 |
| 1 month | 28–31 | 20–23 |
| 90 days | 90 | ~64 |
| 6 months | 181–184 | ~130 |
| 1 year | 365 (366 leap) | ~261 |
| Common notice period | 30 days | ~22 |
| Typical probation | 90 days | ~64 |