Date Difference Calculator
Days Between Dates · Add & Subtract Days · Age in Days
Find the number of days, weeks, months and years between any two dates. Add or subtract days from a date to find a future or past date instantly.
Days Between Two Dates
Add or Subtract Days from a Date
What Is a Date Difference Calculator?
A date difference calculator computes the exact number of days, weeks, months, and years between any two calendar dates. It automatically accounts for leap years (which add an extra day in February every 4 years), making it far more accurate than manual counting.
Common uses include calculating age in days, finding how many days remain until a deadline, determining how long ago an event occurred, and computing contract or visa durations. This tool handles all of these instantly without any arithmetic on your part.
How to Use This Calculator
- Days between dates: Enter a Start Date and an End Date in the top section. Results appear immediately showing the difference in days, weeks, months, and years.
- Add days to a date: In the lower section, enter a Start Date, choose "+ Add", enter the number of days, and the future date is calculated instantly.
- Subtract days from a date: Choose "− Subtract" instead of Add to find a date in the past — useful for deadlines and notice periods.
- Age in days: Enter your birth date as Start Date and today as End Date to see your exact age in all units.
Formula: How Date Differences Are Calculated
The core calculation converts both dates to a Unix timestamp (milliseconds since 1 January 1970) and takes the absolute difference:
Days = |Date2 − Date1| ÷ 86,400,000 ms
From days, the other units are derived:
- Weeks = Days ÷ 7
- Months = Days ÷ 30.44 (average days per month)
- Years = Days ÷ 365.25 (accounts for leap years)
The add/subtract feature simply multiplies the number of days by 86,400,000 ms and adds or subtracts from the start date's timestamp, then formats the result as a date.
Common Date Intervals Quick Reference
| Interval | Exact Days | Approx Weeks | Approx Months |
|---|---|---|---|
| 1 month | 28–31 | 4–4.4 | 1 |
| Quarter (3 months) | 90–92 | ~13 | 3 |
| Half year (6 months) | 181–184 | ~26 | 6 |
| 1 year (regular) | 365 | 52.1 | 12 |
| 1 year (leap) | 366 | 52.3 | 12 |
| 2 years | 730–731 | ~104 | 24 |
| 5 years | 1,826–1,827 | ~261 | 60 |
| 10 years | 3,652–3,653 | ~522 | 120 |
Examples
Example 1: Days until a deadline
If today is 19 April 2026 and your project deadline is 30 June 2026, enter 2026-04-19 as Start Date and 2026-06-30 as End Date. Result: 72 days (10.3 weeks, 2.4 months).
Example 2: Age calculation
Someone born on 1 January 2000 is, as of 19 April 2026, exactly 9,605 days old — or approximately 26.3 years (1,372 weeks).
Example 3: 90 days from today
Starting from 19 April 2026 and adding 90 days gives 18 July 2026. This is a Saturday. Useful for visa durations, payment terms, and Schengen 90/180 day rules.
Example 4: Notice period backdating
If a contract expires on 31 December 2026 and requires 60 days notice, subtracting 60 days gives 1 November 2026 — the last day to submit notice on time.
Tips & Common Mistakes
- Inclusive vs. exclusive counting: The calculator gives the number of days between two dates (exclusive of the start day). If you need to count the start day itself, add 1 to the result.
- Leap years matter: February has 29 days in leap years (2024, 2028…). The calculator handles this automatically.
- Working days: To estimate business days, multiply calendar days by 5/7. Deduct public holidays separately.
- Schengen visa rule: The 90-day Schengen limit is measured over any rolling 180-day period — use the calculator to track your days.
- Daylight saving time: This calculator works on calendar dates, not hours, so DST does not affect results.
Frequently Asked Questions — Date Calculator
Enter today's date as the start date and your future date as the end date. The calculator shows the exact number of days remaining. For example, entering 19 April 2026 and 1 January 2027 gives 256 days until New Year 2027.
Enter your birth date as the start date and today as the end date. The result shows your exact age in days, weeks, months and years. Someone born on 15 March 1990 and calculating on 19 April 2026 is approximately 13,184 days old (36.1 years).
Use the "Add or Subtract Days" section above. Enter today as the start date, select "+ Add", and enter 90 days. The calculator shows the exact date 90 days from now. This is useful for deadlines, contract terms, visa durations and payment due dates.
This calculator shows total calendar days. To estimate working days, multiply calendar days by approximately 5/7 (5 working days out of every 7). For example, 30 calendar days is approximately 21 working days. For precise counts including public holidays, subtract those manually from the total.
Use the "Add or Subtract Days" section. Enter your deadline date as the start date, select "− Subtract", and enter 30 days. The result shows the date exactly 30 days before your deadline. Useful for notice periods, application deadlines and contract milestones.
The calculator handles dates across any year range and accounts for leap years automatically. For example, between 1 January 2020 and 1 January 2025 is exactly 1,827 days — 5 years including the extra leap year days in February 2020 and February 2024.
Use the "Add or Subtract Days" section: enter today's date, select "+ Add", and enter 100. The calculator shows the exact result. Common queries include 30, 60, 90, 180, and 365 days from today — each handled by simply entering the number of days to add.