Date Calculator
Quick References
Related Calculators
Understanding Date Calculations
Common Uses
Project Planning
- • Calculate project timelines
- • Determine milestone dates
- • Count working days
Personal Events
- • Days until a special date
- • Age in days
- • Anniversary countdowns
Legal & Financial
- • Contract expiration dates
- • Interest calculation periods
- • Statute of limitations
Health & Medical
- • Pregnancy due dates
- • Medication schedules
- • Recovery timelines
Understanding Leap Years
A leap year has 366 days instead of 365, with February having 29 days. Leap years occur to keep our calendar aligned with Earth's orbit around the sun.
Leap Year Rules
- The year must be divisible by 4
- If divisible by 100, it must also be divisible by 400
Example: 2000 was a leap year (divisible by 400), but 1900 was not (divisible by 100 but not 400).
Days in Each Month
| Month | Days | Month | Days |
|---|---|---|---|
| January | 31 | July | 31 |
| February | 28/29 | August | 31 |
| March | 31 | September | 30 |
| April | 30 | October | 31 |
| May | 31 | November | 30 |
| June | 30 | December | 31 |
Date Calculation Methods
Exact Day Count
Counts every single day between two dates. Used for interest calculations, age in days, and precise durations.
Calendar Method
Calculates difference in years, months, and days as they appear on a calendar. More intuitive for human understanding (e.g., "2 years, 3 months, 15 days").
Business Days
Excludes weekends and optionally holidays. Used for project planning and legal deadlines that specify "business days."
Interesting Date Facts
- The average month has 30.44 days (365.25 ÷ 12)
- There are exactly 52 weeks and 1 day in a regular year
- The Gregorian calendar was adopted in 1582, skipping 10 days (Oct 4 to Oct 15)
- Different cultures use different calendar systems (Hebrew, Islamic, Chinese, etc.)
- Unix time counts seconds since January 1, 1970 (the "Unix epoch")
Including the End Date
Whether to include the end date depends on context. For "days until" calculations, you typically don't include the end date. For "how many days did I work," you usually do include both the start and end dates. Our calculator gives you the option to choose.
Frequently Asked Questions
How do I calculate the number of days between two dates?
Enter your start date and end date in the calculator above. It will automatically calculate the exact number of days, weeks, months, and years between them. You can also choose whether to include the end date in the count.
What is the difference between calendar days and business days?
Calendar days include all days (weekdays and weekends), while business days typically exclude Saturdays, Sundays, and holidays. Our calculator can show both counts to help with project planning or deadline calculations.
How do leap years affect date calculations?
Leap years add one extra day (February 29) every 4 years, making those years 366 days instead of 365. Our calculator automatically accounts for leap years when calculating days between dates spanning February.
Can I add or subtract days from a specific date?
Yes, use the 'Add/Subtract Days' feature to find a future or past date. Enter your starting date and the number of days to add or subtract, and the calculator will show you the resulting date.