Date Calculator

A date calculator is a free online tool that performs arithmetic with calendar dates. It can find the exact number of days, weeks, months, and years between any two dates, or add and subtract a specified number of days from a given date. This eliminates the tedious process of counting days on a calendar by hand.

Date calculations are more complex than they appear because months have different lengths (28, 29, 30, or 31 days), leap years add an extra day to February, and weekends and holidays complicate business-day counts. Our date calculator handles all of these variables automatically.

Whether you need to know how many days until a contract expires, when a 90-day return window closes, or how many business days remain before a project deadline, this tool gives you the answer instantly. For time-of-day calculations, pair it with the time calculator.

Finding the exact number of days between two dates is the most common use of this tool. Here is how to do it:

1. Enter the start date — Select the year, month, and day using the date picker or type it directly.
2. Enter the end date — Choose the second date in the same way.
3. Click Calculate — The tool instantly displays the difference in multiple formats.
4. Review the results — See the total in days, weeks, months, and years. You can also toggle whether to include the end date in the count.

For example, the difference between January 1, 2025 and March 15, 2025 is 73 days (or 74 if you include the end date). That is 10 weeks and 3 days, or 2 months and 14 days. The date calculator presents all of these formats simultaneously so you can use whichever is most useful for your situation.

A date duration calculator measures the total span of time between two calendar dates. While similar to counting days, a duration calculation can also express the result in larger units like weeks, months, and years for easier comprehension.

This is especially useful for:

• Anniversary tracking — How many years, months, and days since a wedding or business founding.
• Age verification — Precisely how old someone is today (also available in our age calculator).
• Contract duration — The exact length of a lease, subscription, or employment period.
• Historical research — Days between historical events for academic or personal projects.

The duration calculator accounts for the uneven distribution of days across months. A span from January 31 to March 1 is "1 month and 1 day" in a non-leap year, but "1 month" in a leap year because February has 29 days. These nuances are why manual counting so often produces errors.

Sometimes you do not need the difference between two dates — you need to find a future or past date by adding or subtracting a specific number of days, weeks, or months from a known date.

Common examples:

• 90 days from today — Used for return policies, visa validity, and probation periods. If today is March 1, adding 90 days gives you May 30 (or May 29 in a leap year).
• 30 days from a purchase — Warranty start calculations.
• 180 days before a wedding — When to start planning specific tasks.
• Subtract 14 days — Find the start of a two-week quarantine period.

The date calculator handles month-boundary transitions smoothly. Adding 30 days to January 15 gives you February 14, correctly crossing the month boundary. Adding 60 days to December 10 gives you February 8 of the next year. You never have to count on your fingers or flip through calendar pages again.

A business day calculator counts only working days (Monday through Friday), excluding weekends. This is essential for professional deadlines where "10 business days" does not mean 10 calendar days — it means 14 calendar days at minimum, and more if holidays fall within the period.

Our date calculator includes a business-day mode that:

• Excludes Saturdays and Sundays from the count automatically.
• Handles holiday exclusions — You can factor in public holidays for more accurate results.
• Counts forward or backward — Find the date that is 15 business days from today, or count how many business days have passed since a start date.

Business-day calculations are critical for legal filings (court deadlines are often in business days), shipping estimates, financial settlements (T+2 settlement means two business days), and project management timelines. A 30-business-day deadline is actually six calendar weeks, which catches many people off guard.

Leap years occur every four years to keep the calendar aligned with Earth's orbital period. A standard year has 365 days, but a leap year has 366 days due to the extra day added to February (February 29).

The rules for leap years in the Gregorian calendar are:

1. A year divisible by 4 is a leap year.
2. Exception: A year divisible by 100 is NOT a leap year.
3. Exception to the exception: A year divisible by 400 IS a leap year.

So 2024 is a leap year (divisible by 4), 1900 was not (divisible by 100), but 2000 was (divisible by 400). Our date calculator applies these rules automatically when counting days across year boundaries. This matters more than most people realize — a miscounted leap year shifts every subsequent date by one day, which can cause missed deadlines or incorrect age calculations. The age calculator uses the same leap-year logic for birth-date computations.

The date calculator handles a wide variety of real-world scenarios:

• Visa and immigration — Calculate exactly how many days you have spent in a country to stay within allowed limits (e.g., 90 days in a 180-day Schengen period).
• Pregnancy tracking — Count weeks from the last menstrual period to determine gestational age and estimated due date.
• Contract management — Find expiration dates for leases, warranties, and subscription agreements.
• Project timelines — Determine how many working days remain before a launch or deliverable.
• Insurance claims — Many policies have strict filing windows measured in days.
• Academic planning — Count days until exams, semesters, or application deadlines.
• Personal milestones — Days until a wedding, retirement, graduation, or vacation.

In each case, manual counting is slow and error-prone. The date calculator delivers instant, accurate results and presents them in multiple formats — days, weeks, months, and years — so you always have the number you need.

One of the most searched date calculations is the due date for pregnancy. The standard medical method estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP). This is known as Naegele's rule.

Here is how it works:

1. Enter the first day of your last menstrual period as the start date.
2. Add 280 days using the date calculator.
3. The resulting date is your estimated due date (EDD).

For example, if your LMP was June 1, 2025, adding 280 days gives an estimated due date of March 8, 2026. Keep in mind that only about 5% of babies are born on their exact due date — most arrive within a two-week window on either side.

The date calculator can also help track each trimester milestone by adding 84 days (12 weeks) and 182 days (26 weeks) to the LMP date.

Our date calculator uses the Gregorian calendar, the international civil standard adopted by most countries. Introduced by Pope Gregory XIII in 1582, it refined the older Julian calendar by correcting its leap-year rule to better match the solar year.

Key aspects of the Gregorian calendar:

• 12 months with lengths of 28-31 days.
• 365 days per year, with a leap day every 4 years (with century exceptions).
• Average year length of 365.2425 days, very close to the actual solar year of 365.2422 days.

The ISO 8601 standard builds on the Gregorian calendar by defining a consistent date format (YYYY-MM-DD) and week-numbering system. Week 1 of the year is the week containing the first Thursday, and weeks always start on Monday.

When using the date calculator for historical dates before 1582, be aware that some regions used the Julian calendar, which can differ by several days. For most modern calculations, the Gregorian system is all you need.

Project managers rely on date calculations daily. From sprint planning in agile development to milestone tracking in construction projects, knowing the exact number of days between dates is essential for staying on schedule.

Here is how the date calculator supports project management:

• Sprint boundaries — A two-week sprint starting on Monday, March 3 ends on Friday, March 14 (10 business days later).
• Milestone tracking — If a project kicked off on January 15 and has a 120-day timeline, the deadline falls on May 15.
• Buffer calculation — Add contingency days to each phase to build in schedule padding.
• Retrospective analysis — Count actual days spent versus estimated days to improve future planning.

The business-day mode is especially valuable because project deadlines almost always exclude weekends. A "30-day" project typically means 30 business days, which spans six calendar weeks. Using the date calculator prevents the common mistake of treating business days as calendar days, which can cause teams to miss deadlines by over a week. Combine it with the time calculator for hour-level tracking within each workday.