- How to Use the Date Difference Calculator
- How Date Difference Is Calculated
- Practical Examples
- Example 1: How many days until a deadline?
- Example 2: How long have I been alive?
- Example 3: What date is 90 days from now?
- Frequently Asked Questions
- How many days are in a year?
- How do you calculate business days between two dates?
- What is the date 30 days from today?
- How do I calculate the number of weeks between two dates?
Date Difference Calculator
Find the exact days, months & years between any two dates
How to Use the Date Difference Calculator
Our free date difference calculator has two modes:
- Days Between Dates — Enter a start date and an end date to find the exact difference in years, months, days, weeks, hours, minutes, and business days.
- Add/Subtract Days — Enter a start date and a number of days (positive to add, negative to subtract) to find the resulting date.
The calculator automatically detects the day of the week for both dates and calculates business days (excluding weekends).
How Date Difference Is Calculated
Calculating the exact difference between two dates requires handling several complexities:
- Variable month lengths — Months range from 28 to 31 days. February has 28 days (29 in leap years).
- Leap years — Years divisible by 4 are leap years, except centuries not divisible by 400 (so 2000 was a leap year, but 1900 was not).
- Business days — Weekdays (Monday–Friday) only, excluding Saturdays and Sundays.
The formula works by: subtracting years, then months, then days — adjusting for negative results by borrowing from the next larger unit (similar to subtraction with borrowing in arithmetic).
Practical Examples
Example 1: How many days until a deadline?
Your project deadline is December 31, 2026 and today is July 14, 2026. The difference is 170 days (or about 24 weeks and 2 days). That’s approximately 121 business days to complete your work.
Example 2: How long have I been alive?
Born on March 15, 1995, and today is July 14, 2026: that’s 31 years, 3 months, and 29 days — or approximately 11,444 days (about 274,656 hours).
Example 3: What date is 90 days from now?
Starting from July 14, 2026, adding 90 days: the result is October 12, 2026 (Monday). This is useful for contract deadlines, trial periods, and warranty expiration dates.
Frequently Asked Questions
How many days are in a year?
A regular year has 365 days, while a leap year has 366 days. For precise calculations over long periods, the average year length is 365.2425 days (accounting for the leap year cycle).
How do you calculate business days between two dates?
Business days exclude Saturdays and Sundays. Count all days between the two dates, then subtract the number of weekend days. Our calculator does this automatically. Note that official holidays are not excluded — these vary by country and region.
What is the date 30 days from today?
Use the “Add/Subtract Days” tab and enter 30 in the days field. The calculator will show you the exact date and day of the week. This is commonly needed for billing cycles, payment terms, and trial periods.
How do I calculate the number of weeks between two dates?
Take the total number of days between the two dates and divide by 7. For example, 45 days = 6 weeks and 3 days. Our calculator shows both total weeks and remaining days automatically.