Date Calculator
This date calculator finds the exact number of days, weeks, months, and years between any two dates. You can also add or subtract days from a specific date to find a future or past date, with options to count only business days.
Frequently Asked Questions
How do you calculate days between two dates?
To calculate days between two dates, subtract the earlier date from the later date. Convert both dates to a common reference (such as Julian Day Number or Unix timestamp), then find the difference. For example, from January 1 to March 15 in a non-leap year: 31 days (Jan) + 28 days (Feb) + 15 days (Mar) = 74 days. Our calculator handles all the complexity of varying month lengths, leap years, and calendar rules automatically.
How do you add days to a date?
To add days to a date, start from the given date and count forward the specified number of days, accounting for varying month lengths and leap years. For example, adding 45 days to January 20 means counting through the remaining 11 days of January (to Jan 31), all 28 days of February (non-leap year), and 6 more days into March, giving you March 6. Our calculator handles this instantly for any number of days.
How many days are in a year?
A common year has 365 days, while a leap year has 366 days. Leap years occur every 4 years (divisible by 4), except for century years (divisible by 100) unless they're also divisible by 400. So 2024 is a leap year, 1900 was not, but 2000 was. The average length of a year in the Gregorian calendar is 365.2425 days. This is important for accurate date calculations spanning multiple years.
How do you count business days between dates?
To count business days (weekdays), calculate the total days between two dates and subtract weekends. For each complete week, there are 5 business days. Count the remaining partial week days individually, excluding Saturdays and Sundays. For example, Monday to the following Friday is 5 business days (but 5 calendar days if same week, or 12 calendar days if next week). Note that public holidays are not automatically excluded unless specifically accounted for.
How do leap years affect date calculations?
Leap years add February 29, making the year 366 days instead of 365. This affects date calculations spanning February in a leap year. A leap year occurs when the year is divisible by 4, except for century years unless divisible by 400. When calculating days between dates across leap years, each leap year adds one extra day. For example, from Jan 1 to Dec 31 is 364 days in a common year but 365 days in a leap year.
How many weeks between two dates?
To find weeks between two dates, first calculate the total number of days between them, then divide by 7. For example, 45 days between two dates equals 6 weeks and 3 days (6 complete weeks with a 3-day remainder). If you need only complete weeks, round down. For partial weeks, the remainder tells you the extra days. Our calculator provides both the exact week count and the remaining days.
How do you calculate age from a date?
To calculate age from a birth date, find the difference between today's date and the birth date in years, months, and days. Start by subtracting the birth year from the current year. If the current month and day are before the birth month and day, subtract one year (the birthday hasn't occurred yet this year). Then calculate remaining months and days similarly. For example, someone born March 15, 1990 is 35 years old on January 1, 2026 (birthday hasn't passed yet in 2026).
What is a Date Calculator?
A date calculator is a versatile tool for performing arithmetic with calendar dates. Our date calculator lets you find the exact number of days between two dates or calculate a future or past date by adding or subtracting a specific number of days. Whether you need to determine project timelines, count down to deadlines, or plan events, the date calculator provides instant, accurate results broken down into days, weeks, months, and years.
How to Use the Date Calculator
Calculate Days Between Two Dates
- Select the "Days Between" tab
- Enter a start date using the date picker
- Enter an end date using the date picker
- View the result instantly as total days, weeks and days, months and days, or years, months, and days
Add or Subtract Days from a Date
- Select the "Add/Subtract Days" tab
- Choose a starting date
- Enter the number of days to add or subtract
- Toggle between "Add" and "Subtract" mode
- The resulting date is displayed immediately
How Days Between Dates is Calculated
The date calculator computes the difference between two dates by converting each date into a timestamp (milliseconds since January 1, 1970) and finding the absolute difference. The result is then converted into calendar units:
- Total Days: The absolute difference in milliseconds divided by the number of milliseconds in a day (86,400,000).
- Weeks + Days: Total days divided by 7, with the remainder as extra days.
- Years, Months, Days: Calendar-aware calculation that accounts for varying month lengths and leap years.
Examples
Days Between January 1 and December 31
From January 1 to December 31 of the same year is 364 days (365 in a leap year). The date calculator breaks this down as 52 weeks and 0 days, or 11 months and 30 days.
Adding 90 Days to a Date
Adding 90 days to March 1, 2025 gives May 30, 2025. This is useful for calculating quarterly deadlines, warranty expiration dates, or trial period end dates.
Common Use Cases
- Project management: Calculate durations and deadlines
- Legal and contractual: Determine notice periods and filing deadlines
- Healthcare: Track treatment cycles and follow-up appointments
- Education: Count school days and semester lengths
- Personal: Plan vacations, count days until events, or track milestones
- Finance: Calculate interest accrual periods and payment schedules
Tips for Using the Date Calculator
- The order of start and end dates does not matter — the calculator always returns a positive difference
- Use the "Add/Subtract" tab to quickly find future or past dates relative to today
- Copy results to your clipboard with a single click for easy sharing
- The "Years + Months + Days" breakdown accounts for calendar-specific month lengths, providing the most human-readable result