Date Calculator
Calculate days between two dates, add or subtract days, or find out how long until an event.
What is a date calculator used for?
Calculating days between dates is more useful than it might seem — from knowing how many days you have been in a new job to planning how much time is left before an important event:
📅 Personal planning
Count the days until your holiday, wedding, an exam or any date you mark on the calendar.
💼 Professional use
Calculate delivery deadlines, probationary periods, contract expiry dates or seniority with precision.
⚖️ Legal matters
Many legal deadlines are measured in calendar days. Add exactly the number of days indicated in a notice or resolution.
🏥 Health tracking
Keep track of days since an operation, the start of a treatment, or your last medical check-up.
Calendar days vs working days
It is important to distinguish between the two types of days commonly used:
- Calendar days: all days including Saturdays, Sundays and public holidays. These are the days this calculator uses.
- Working days: only business days (usually Monday to Friday), excluding weekends and official holidays. These are commonly used in administrative and legal procedures.
How is the difference between two dates calculated?
The calculation is based on subtracting the numeric values of both dates. JavaScript represents each date as the number of milliseconds elapsed since 1 January 1970. By subtracting both and dividing by 86,400,000 (the milliseconds in a day), we obtain the exact difference. For the breakdown into years, months and days, the actual length of each month and leap years are taken into account.
| Period | Approximate days |
|---|---|
| 1 week | 7 days |
| 1 month (average) | 30.44 days |
| 1 quarter | 91 days |
| 1 normal year | 365 days |
| 1 leap year | 366 days |
| 1 decade | 3,652 days |
Frequently asked questions about date calculation
How are days between two dates calculated?
The start date is subtracted from the end date in milliseconds and the result is converted to days by dividing by 86,400,000. Our calculator does this automatically and also shows the breakdown in years, months and days.
Do leap years affect the calculation?
Yes. A leap year has 366 days instead of 365. Our calculator accounts for them automatically to always give an exact result.
Can I calculate how many days are left until a future date?
Yes. In the Days until an event tab, enter the event date and you will see exactly how many days, weeks and months are left.
What if I add days and land on a weekend or holiday?
The calculator shows the exact date resulting from adding or subtracting calendar days, without excluding weekends or holidays. If you need working days only, please account for this manually.