Date Calculator
Find the number of days between two dates, or add and subtract days from any date. Results include weeks, workdays, and a years-months-days breakdown.
Date Difference
Days between two dates
Add / Subtract
Add or subtract days
Quick Examples
What Is a Date Calculator?
A date calculator performs calendar arithmetic: it counts the exact number of days between two dates, or finds the date that falls a given number of days before or after a starting date. It answers questions like "how many days until the deadline?", "when does a 90-day notice period end?", and "how many workdays are left this quarter?"
Counting days by hand across month boundaries is slow and error-prone — months have 28 to 31 days and leap years insert an extra day every four years. The calculator above handles all of that automatically, showing total days, weeks, workdays, and a calendar-accurate years-months-days breakdown.
Days Between Two Dates: Exclusive Counting
The number of days between two dates is the count of calendar days from the earlier date to the later date, not counting the start date itself. This is called exclusive counting and it is the standard mathematical convention:
- January 1 to January 5 = 4 days (January 2, 3, 4, 5)
- January 1 to February 1 = 31 days (all of January)
- January 1 to December 31 in a non-leap year = 364 days
- June 14 to December 25, 2026 = 194 days
Think of it like hotel nights: check in on Monday, check out on Friday — you stayed 4 nights, not 5. The arrival day is day zero. If your situation needs inclusive counting (both dates counted, as in "a 3-day event running Thursday to Saturday"), add 1 to the result or tick the include-end-date checkbox.
This distinction decides real deadlines. "30 days from January 1" ends on January 31 under exclusive counting (January 1 is day 0), but on February 1 if the document counts January 1 as day 1. Always check whether your contract counts the start date as day 0 or day 1.
Workdays vs. Calendar Days
The calculator shows both total calendar days and workdays (Monday through Friday), because the two answer different questions:
| Use Case | Which Count to Use |
|---|---|
| Payment terms (Net 30, Net 60) | Calendar days |
| Project deadlines from a contract date | Calendar days, unless the contract says business days |
| Statutory notice periods | Calendar days in most jurisdictions |
| Delivery estimates from a carrier | Workdays |
| Sprint and task effort estimation | Workdays |
| Bank processing times | Workdays, often excluding public holidays |
A standard year contains 260 to 262 workdays, depending on how weekends align with January 1 and December 31. Public holidays are not excluded automatically because they vary by country and employer — subtract weekday holidays manually for a holiday-adjusted count.
Leap Years
February has 29 days in a leap year and 28 otherwise. A year is a leap year if divisible by 4, except century years (1900, 2100), which must also be divisible by 400 — so 2000 was a leap year but 1900 was not. Any range crossing February of a leap year is exactly 1 day longer than the same range in a non-leap year.
Adding and Subtracting Days
Adding or subtracting days shifts the calendar by exactly one position per day, regardless of month boundaries or leap years:
- Contract deadlines: a 30-day payment term on a March 15 invoice falls on April 14.
- Notice periods: a 90-day notice starting October 1, 2026 ends December 30, 2026.
- Free trials: a 14-day trial starting November 20 ends December 4.
- Medication courses: a 28-day course starting January 3 ends January 31.
- Returns: a 30-day return window on a December 1 purchase expires December 31.
Month and Year Arithmetic
The years-months-days breakdown uses exact calendar months, which differs from dividing the day count by 30. A complete calendar month elapses when the end date's day-of-month reaches the start date's day-of-month:
| Start Date | End Date | Breakdown |
|---|---|---|
| Jan 1 | Feb 1 | 1 month, 0 days |
| Jan 1 | Mar 15 | 2 months, 14 days |
| Jan 31 | Feb 28 | 0 months, 28 days |
| Jan 31 | Mar 1 | 1 month, 1 day |
| Jan 31 | Mar 31 | 2 months, 0 days |
| Dec 31, 2023 | Jan 1, 2024 | 0 months, 1 day |
Adding 1 month is not the same as adding 30 days. January 31 plus one calendar month is February 28 (clamped to the last valid day), not March 2. The Add / Subtract mode adds calendar days only.
How to Calculate Days Between Dates by Hand
For a quick estimate: multiply complete years by 365.25 (the .25 accounts for leap years), add leftover months multiplied by 30.4375 (the average month), add the leftover days, and round. Within a single month it is simpler: 22 days lie between July 4 and July 26 (26 − 4 = 22), or 23 counting the end date.
Common Date-Calculation Mistakes
- Off by one: exclusive vs. inclusive. Decide up front whether the start date counts as day 0 or day 1 — critical for legal deadlines.
- Treating all months as 30 days. Dividing a day count by 30 is an approximation; twelve months are 365 or 366 days, not 360.
- Confusing workday conventions. Excel's NETWORKDAYS counts both endpoints inclusively — 1 more than an exclusive workday count.
- Mixing month and day arithmetic. "One month from January 31" and "30 days from January 31" land on different dates.
Excel and Google Sheets Formulas
| What to Calculate | Formula | Notes |
|---|---|---|
| Days between two dates | =B1-A1 | Format the cell as a number |
| Workdays between two dates | =NETWORKDAYS(A1,B1) | Inclusive of both dates; optional holiday range |
| Add N days to a date | =A1+30 | Format the result as a date |
| Add N workdays to a date | =WORKDAY(A1,30) | Skips weekends; optional holiday range |
| Complete years elapsed | =DATEDIF(A1,B1,"Y") | Undocumented but works in all Excel versions |
| Remaining months / days | =DATEDIF(A1,B1,"YM") / "MD" | After complete years / months are removed |
Frequently Asked Questions
Conclusion
Date arithmetic looks simple until month lengths, leap years, weekends, and the exclusive-versus-inclusive question get involved. Remember: day counts exclude the start date by convention (add 1 for inclusive counting), and calendar months are not interchangeable with 30-day blocks.
Use the date calculator above to count the days between any two dates or add and subtract days — with weeks, workdays, and a calendar-accurate breakdown computed instantly.