Math
Date Difference Calculator
Calculate the exact number of days, weeks, months, and hours between any two dates. Find countdowns to future events, days since past events, business days, and precise date durations.
Quick presets
Useful Date & Calendar Facts
| Period | Days | Weeks | Hours |
|---|---|---|---|
| 1 week | 7 | 1 | 168 |
| 1 month (avg) | 30.44 | 4.35 | 730 |
| 1 quarter | 91 | 13 | 2,184 |
| 6 months | 182 | 26 | 4,380 |
| 1 year | 365 | 52 | 8,760 |
| 1 leap year | 366 | 52.3 | 8,784 |
| 5 years | 1,826 | 261 | 43,824 |
| 10 years | 3,653 | 521 | 87,672 |
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Frequently Asked Questions
How do I calculate the number of days between two dates?
Subtract the earlier date from the later date. Each day = 86,400 seconds = 86,400,000 milliseconds. In practice: convert both dates to a numerical value (milliseconds since Jan 1, 1970), subtract, and divide by 86,400,000. This calculator handles all of that automatically including leap years and month-length differences.
How many days are in a year?
A regular year has 365 days. A leap year has 366 days. Leap years occur every 4 years, except for century years not divisible by 400. So 2000 and 2400 are leap years, but 1900 and 2100 are not. On average, a year has 365.2425 days. Over a 4-year period: 365 + 365 + 365 + 366 = 1,461 days ÷ 4 = 365.25 days/year.
What are business days and how are they counted?
Business days (also called working days) are weekdays — Monday through Friday — excluding weekends (Saturday and Sunday). They do not automatically exclude public holidays, as these vary by country, region, and employer. To count business days between two dates: count all calendar days and subtract Saturdays and Sundays. This calculator shows business days for ranges up to 2 years.
How many weeks are in a year?
A regular year has 52 weeks and 1 day (365 ÷ 7 = 52.14 weeks). A leap year has 52 weeks and 2 days. The ISO week numbering system defines a year as having either 52 or 53 weeks — years with 53 weeks occur when January 1st falls on a Thursday (or Wednesday in a leap year).
How do I calculate how many months between two dates?
Count the full calendar months between the two dates, adjusting for day-of-month differences. For example, from March 15 to June 10 is 2 full months and 26 days (not quite 3 months). From Jan 1 to Dec 31 is 11 months and 30 days (not 12 full months). This calculator shows both total months and the year/month/day breakdown.
Does this calculator include or exclude the end date?
This calculator counts days from the start date up to but not including the end date. For example, from January 1 to January 3 = 2 days (Jan 1 and Jan 2). To include the end date in your count, simply add 1 to the result. This is the standard convention for date difference calculations.
How do I calculate days until a future event?
Set today as your start date and your event date as the end date. The result is the number of days remaining until your event. Common uses: days until a birthday, wedding, vacation, project deadline, exam, or holiday. The calculator also shows weeks and months so you can plan at different time scales.