Calculate days between dates, add or subtract time from any date, and count business days excluding weekends and holidays. Free, instant, handles leap years automatically.
This is the single most common source of "off by one" errors in date calculations. The two methods give genuinely different answers, and which one applies depends entirely on context.
| Method | Jan 1 to Jan 3 equals | Used For |
|---|---|---|
| Exclusive (gap only) | 2 days | Hotel nights, elapsed time, "how many days until" |
| Inclusive (both count) | 3 days | Eligibility periods, legal notice periods, billing cycles |
Hotel bookings almost always use exclusive counting — checking in on Jan 1 and checking out on Jan 3 means 2 nights stayed. Legal notice periods and eligibility windows often use inclusive counting — "you have 3 days from January 1st" typically means January 1, 2, and 3 all count. Always read the specific contract, rule, or policy carefully rather than assuming. The calculator above lets you toggle between both methods.
"Business days" isn't universal — different countries have different weekend days and different public holiday calendars, which matters for international contracts and shipping estimates.
| Country/Region | Weekend Days | Typical Annual Public Holidays |
|---|---|---|
| United States | Saturday, Sunday | 11 federal holidays |
| United Kingdom | Saturday, Sunday | 8 bank holidays |
| Canada | Saturday, Sunday | 9-10 (varies by province) |
| Australia | Saturday, Sunday | 8-13 (varies by state) |
| UAE / Saudi Arabia | Friday, Saturday | varies, often Islamic calendar-based |
| Israel | Friday, Saturday | varies, Hebrew calendar-based |
Our Business Days calculator above uses the standard Saturday/Sunday weekend and optionally excludes the 11 major US federal holidays. For countries with different weekend conventions or holiday calendars, manually adjust the total by the relevant difference.
A leap year adds February 29th to keep the calendar aligned with Earth's orbit, which takes approximately 365.2422 days. Without leap years, the calendar would drift by about 1 day every 4 years.
The leap year rule: A year is a leap year if divisible by 4 — EXCEPT century years (divisible by 100), which are NOT leap years — UNLESS also divisible by 400. So 2024 and 2028 are leap years. 2100 will NOT be a leap year despite being divisible by 4. 2000 WAS a leap year because it's divisible by 400.
| Year | Leap Year? | Why |
|---|---|---|
| 2024 | Yes | Divisible by 4, not a century year |
| 2026 (current) | No | Not divisible by 4 |
| 2028 | Yes | Divisible by 4, not a century year |
| 2000 | Yes | Divisible by 400 |
| 2100 | No | Divisible by 100, but not 400 |
Our calculator handles all leap year logic automatically — every "days between dates" and "add/subtract" calculation correctly accounts for February having 29 days in leap years and 28 in regular years.
One of the most common sources of real-world errors — missed flights, contract disputes, software bugs — is date format ambiguity between countries.
| Format | 03/04/2026 means | Used In |
|---|---|---|
| MM/DD/YYYY | March 4, 2026 | United States |
| DD/MM/YYYY | April 3, 2026 | UK, Europe, most of the world |
| YYYY-MM-DD (ISO 8601) | Unambiguous | International standard, technical/legal documents |
💡 Best practice: Whenever writing a date for an international audience, a contract, or any technical context, use ISO 8601 format (YYYY-MM-DD) — for example, 2026-04-03. It's unambiguous, and as a bonus, it sorts correctly alphabetically/numerically, which is why it's the standard for filenames, databases, and APIs worldwide.
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