Days Between Dates Calculator

Convert both dates to milliseconds (Unix timestamp — milliseconds since January 1, 1970), subtract them, and divide by 86,400,000 (milliseconds per day). Example: days between January 1 and December 31 = (Dec 31 ms − Jan 1 ms) / 86,400,000 = 364 days (in a non-leap year). Our calculator does this automatically and also computes weeks, months, business days, hours, and minutes from the total.

Business days (also called working days) are Monday through Friday, excluding Saturdays and Sundays. This calculator counts all weekdays between the two dates. It does not exclude public holidays, which vary by country, state, and employer. For legal contracts or delivery deadlines that exclude specific public holidays, you will need to subtract those manually. In the US, there are typically 260–262 business days per year (depending on how weekends fall).

A standard (common) year has 365 days. A leap year has 366 days, with February 29 added. Leap years occur every 4 years, except for century years not divisible by 400. So 2000 was a leap year (divisible by 400), but 1900 was not (divisible by 100 but not 400). The next century year is 2100, which will not be a leap year. The average Gregorian year is 365.2425 days, keeping the calendar aligned with Earth's orbit over centuries.

Set Start Date to today using the "Today" button, then enter your next birthday as the End Date. The calculator will show exactly how many days remain. If you want to know your age in days, set Start Date to your birth date and End Date to today. The result is the total number of days you have been alive. For a fun twist, check our Seconds Alive calculator to see your age in seconds.

Calendar days include every day of the week — Monday through Sunday, including holidays. Working days (business days) exclude Saturdays and Sundays and may also exclude public holidays. Example: if a contract says "deliver in 10 business days" starting Monday, the deadline is the Friday two weeks later. If it says "10 calendar days," the deadline is the Thursday of the following week. Always clarify which type is meant in legal, financial, or shipping contexts.

January: 31. February: 28 (29 in leap years). March: 31. April: 30. May: 31. June: 30. July: 31. August: 31. September: 30. October: 31. November: 30. December: 31. A quick mnemonic: count on your knuckles — knuckles are 31-day months, valleys between knuckles are 30-day months (or 28/29 for February). The months 7, 8, 9 (July, August, September) use the same knuckle-valley-knuckle pattern starting from the index finger.

Months = (end year − start year) × 12 + (end month − start month). Example: January 15, 2024 to August 20, 2026 = (2026−2024) × 12 + (8−1) = 24 + 7 = 31 months. If the end day is before the start day, subtract 1 month and add the remaining days. This calculator gives the whole-month count; the "exact duration" field shows years, months, and remaining days together for a complete breakdown.

A Julian Day Number (JDN) is a continuous count of days since the beginning of the Julian Period (January 1, 4713 BC). It is widely used in astronomy and computing to simplify date arithmetic — subtracting two Julian Day Numbers gives the exact number of days between them without dealing with months, leap years, or calendar reforms. For example, J2000.0 (January 1.5, 2000, i.e., noon on January 1, 2000) = JDN 2,451,545. Software date libraries often use similar internal representations (Unix timestamps in seconds or milliseconds).

A business quarter is approximately 91 days (one quarter of 365). Q1 (Jan–Mar) = 90 days (91 in a leap year). Q2 (Apr–Jun) = 91 days. Q3 (Jul–Sep) = 92 days. Q4 (Oct–Dec) = 92 days. Total: 365 days. Financial quarters are used for earnings reports, tax filings, and budgeting. Fiscal year quarters may differ from calendar quarters — some companies start their fiscal year in July or October.

Some interesting historical dates to calculate from: Apollo 11 Moon landing: July 20, 1969. World War II ended (VJ Day): September 2, 1945. The French Revolution (Bastille Day): July 14, 1789. Shakespeare's birth: April 23, 1564. The fall of the Roman Empire (Western): September 4, 476 AD. Columbus reached the Americas: October 12, 1492. The signing of the Magna Carta: June 15, 1215. Enter any of these as the Start Date and today as the End Date to see how many days have passed.