Date Calculator
Calculate the difference between dates or add/subtract days from a date.
Days between
Add / subtract days
What is a date calculator?
A date calculator computes the difference between two dates or adds/subtracts a duration from a date. How many days until your vacation? How many weeks between two events? What date is 90 business days from now? This tool answers all these questions instantly, handling the complexities of varying month lengths and leap years.
Date arithmetic is surprisingly complex because months have different lengths (28-31 days), years can be 365 or 366 days, and business days exclude weekends and optionally holidays. This tool handles all these cases and presents results in multiple formats: total days, weeks and days, months and days, and years.
How to use this tool
To find the duration between two dates: enter the start and end dates. The tool shows the difference in days, weeks, months, and years. To add or subtract time from a date: enter a start date and a duration (days, weeks, months, or years). The tool calculates the resulting date.
Business days calculation
Business days (also called working days) exclude weekends (Saturday and Sunday). Some calculations also exclude public holidays. Business day calculations are important for legal deadlines, shipping estimates, project timelines, and financial settlement periods. A 30-day deadline is very different from a 30-business-day deadline — the latter is about 6 calendar weeks.
Leap year rules
A year is a leap year if it is divisible by 4, except for century years (divisible by 100) which must also be divisible by 400. So 2024 is a leap year, 1900 was not, and 2000 was. Leap years add February 29, making the year 366 days instead of 365. This tool correctly handles leap years in all calculations.
Frequently asked questions
How do I calculate my exact age in days?
Enter your birth date as the start date and today's date as the end date. The tool shows your age in total days, as well as years, months, and days. A person born on January 1, 2000, was 9,131 days old on January 1, 2025. The tool handles leap years automatically in this calculation.
What about dates before the year 1?
This tool works with dates in the common era (CE/AD). Calculations involving dates before year 1 (BCE/BC) require special handling of the proleptic Gregorian calendar and the fact that there is no year 0 in the traditional calendar. For historical dates, the results may differ from some sources that use different calendar systems.