Date Calculator

To calculate days between two dates, subtract the earlier date from the later date and count each complete 24-hour period as one day. For example, from January 15, 2024 to March 10, 2024 is 55 days (31 remaining days in January + 29 days in February [leap year] + 10 days in March = 70 total - 15 start day = 55 days). This calculation must account for varying month lengths (28-31 days) and leap years where February has 29 days instead of 28. Our calculator automatically handles these complexities, showing total days plus breakdowns in weeks (divide days by 7), months, and years. This calculation is useful for project deadlines, vacation planning, age calculations, and determining how many days until important events. You can also use our Age Calculator to find exactly how many days old you are.

To add days to a date, count forward that many days accounting for month-end rollovers and leap years. For example, adding 45 days to January 20, 2024 means: 11 remaining January days + 29 February days (2024 is a leap year) + 5 March days = March 5, 2024. To subtract days, count backward through previous months. Subtracting 45 days from March 10, 2024 means: 10 March days + 29 February days + 6 January days (45 - 10 - 29 = 6) = January 6, 2024. Our calculator handles these calculations automatically, including when you add months or years, which is more complex (adding 1 month to January 31 becomes February 28/29 since February doesn't have 31 days). For more precise time-based calculations including hours and minutes, try our Time Calculator. This feature is essential for calculating payment due dates, project deadlines, subscription renewals, or pregnancy due dates.

Business days (also called working days or weekdays) exclude Saturdays and Sundays from the total day count. To calculate manually, first find total calendar days between dates, then subtract the number of weekend days. For example, 14 calendar days contains 2 full weeks = 4 weekend days (2 Saturdays + 2 Sundays), leaving 10 business days. For partial weeks, identify which day of the week each date falls on and count only Monday through Friday. A period from Monday to Friday of the same week is 5 business days, but Monday to Monday next week is 6 business days (excluding 2 weekend days). Business day calculations are crucial for contract deadlines, shipping estimates, and legal timeframes which often specify "within 5 business days." For calculating work hours and duration across business days, check out our Hours Calculator. Note that business day calculations typically don't account for public holidays, which would further reduce the count in real-world applications.

Calendar days (also called consecutive days) include every single day in a period including weekends and holidays, while business days exclude Saturdays, Sundays, and sometimes public holidays. For example, "within 10 calendar days" of January 15 means by January 25 (regardless of weekends), but "within 10 business days" means 10 weekdays, which could be January 29 after excluding 4 weekend days. This difference significantly impacts deadlines: 30 calendar days is always approximately one month, but 30 business days is about 6 weeks (30 weekdays + 8-12 weekend days). Legal contracts, shipping policies, and return periods must specify which type of days they mean. Banks and government agencies typically use business days for processing times ("allow 3-5 business days for processing"), while insurance, leases, and medical contexts often use calendar days. Always clarify which type applies to avoid missing important deadlines.

Leap years add one extra day (February 29) every 4 years, affecting date calculations that span February in a leap year. Leap years occur in years divisible by 4, except century years which must be divisible by 400 (so 2000 was a leap year but 1900 was not). For example, days between January 1, 2024 and March 1, 2024 is 60 days (including February 29), but the same period in non-leap year 2023 is only 59 days. When adding or subtracting years, be careful: adding "1 year" to February 29, 2024 is technically March 1, 2025 (or February 28, 2025) since 2025 is not a leap year. This affects age calculations for people born on February 29 (they "officially" age only every 4 years), loan amortization schedules, and long-term project planning. Our calculator automatically detects and accounts for leap years in all calculations to ensure accuracy across any date range.

To calculate complete weeks between two dates, first calculate total days, then divide by 7 and round down to get full weeks. For example, 50 days ÷ 7 = 7 complete weeks with 1 day remaining (7 × 7 = 49, leaving 1 day). If you need to know weeks and days separately, use the remainder: 50 days = 7 weeks, 1 day. For pregnancy tracking, healthcare often counts in "weeks + days" format (like "28 weeks, 3 days pregnant"). Note that "weeks between dates" can mean different things: some contexts want Sunday-to-Saturday week blocks, others want any 7-day period. For example, from Friday to Sunday of next week could be "1 complete week" or "2 partial weeks" depending on definition. Our calculator shows total complete weeks (any 7-day periods) plus remaining days for clarity. This calculation helps with project scheduling, pregnancy tracking, and subscription billing cycles.

To calculate a future date, add your desired time period (days, weeks, months, or years) to today's date, accounting for month lengths and leap years. For example, 90 days from January 15, 2024: 16 remaining January days (31 - 15 = 16) + 29 February days (leap year) + 31 March days + 14 April days = April 14, 2024 (16 + 29 + 31 + 14 = 90). For months, remember that "3 months from January 31" becomes April 30 (not April 31) because not all months have 31 days. Adding years is simpler: 1 year from February 29, 2024 is technically February 28, 2025 (or March 1) since 2025 isn't a leap year. Use our "Add or Subtract Time" calculator above to automatically compute future dates, which is essential for calculating loan payment due dates, project deadlines, subscription renewals, or planning events. You can also use our Age Calculator to determine your exact age on a future date.

Date calculators may give different results due to variations in how they handle month boundaries, leap years, or whether they count the start/end dates inclusively or exclusively. For example, "days between January 1 and January 10" could be 9 days (excluding start date) or 10 days (including both dates). Some calculators use average month lengths (30.44 days) for month calculations, while others use exact calendar months, leading to different "months between dates" results. Time zone differences can also cause one-day variations if calculators use server time vs. user local time. Additionally, some calculators may incorrectly handle leap year rules (missing the century exception: 1900 wasn't a leap year). Our calculator uses exact calendar date arithmetic with proper leap year handling and excludes the start date when counting "days between" (so January 1 to January 2 is 1 day, not 2). Always verify that dates are entered in the correct format (MM/DD/YYYY vs DD/MM/YYYY) to avoid confusion.

For project planning, calculate deadlines by working backward from your target completion date or forward from your start date, accounting for business days, holidays, and task dependencies. For example, if a project launches on June 1 and requires 20 business days of testing, start testing by May 3 (counting backward 20 weekdays, approximately 28 calendar days with weekends). Break projects into milestones: "90 days total project" might be divided into 30-day phases, with specific deadlines calculated using a date calculator. Always add buffer time: if something needs "30 days," calculate 35-40 days to account for unexpected delays. Consider critical dates like holidays, team availability, and fiscal year ends that might impact your timeline. Use the "Add/Subtract Time" calculator to establish milestone dates (kickoff + 45 days = design review), then use "Days Between Dates" to verify time allocations are realistic. For detailed scheduling, calculate both calendar days (for overall timeline) and business days (for work requiring staff availability).

Pregnancy due dates are calculated by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP), which is the medical standard called Naegele's Rule. For example, if LMP was January 1, 2024, add 280 days to get due date of October 7, 2024. Alternatively, add 7 days to LMP date then count forward 9 months (January 1 + 7 days = January 8, then 9 months forward = October 8, approximately). Healthcare providers adjust this estimate based on early ultrasound measurements, which are more accurate between 8-13 weeks. Remember that only 4-5% of babies are born on their exact due date; "full term" is actually 37-42 weeks (259-294 days), a 35-day range. Pregnancy is tracked in "weeks + days" format using the due date as reference (like "28 weeks, 3 days pregnant"). Use our "Add or Subtract Time" calculator to add 280 days to your LMP date, or consult our Age Calculator to calculate baby's age after birth. Always verify dates with your healthcare provider as individual circumstances may require adjusted calculations.