Use this free days between dates calculator to count the exact number of days between any two dates. If you need to calculate days between two dates for a contract, project, or countdown, this days calculator between two dates will help you find the total day count instantly, including weeks, decimal weeks, and leap years.
How to use this days between dates calculator
Dates can be entered in any order - this days calculator between two dates always counts from the earlier date to the later one to calculate days between dates accurately.
How to calculate days between two dates
Learning how to calculate days between two dates by hand requires a method that correctly handles months of different lengths and leap years. This days between dates calculator uses Unix timestamps - converting each date to a count of milliseconds since midnight January 1, 1970, subtracting, and dividing by 86,400,000 (the number of milliseconds in one day) to calculate days between dates.
This one-step arithmetic handles everything automatically. Every February 29 in the range contributes its full 86,400,000 milliseconds to the difference; no extra code is needed to detect leap years. The result is always a whole number because both dates are normalised to midnight before conversion.
Why 86,400,000 milliseconds per day?
One day = 24 hours x 60 minutes x 60 seconds x 1,000 milliseconds = 86,400,000 ms. This value is fixed for all calendar days except on days that cross a daylight saving time transition. Because both dates are set to midnight in the local calendar (not a UTC offset), DST transitions do not affect the count - any clock-shift is applied equally to both endpoints.
The formula
What does "days between dates" mean?
Knowing how many days between dates exist is the count of calendar days separating two date points. It answers the question: "if I start on date A and finish on date B, how many days is that?" and is the core question our day calculator between dates answers across an enormous range of practical contexts.
In finance, simple interest accrues daily. To calculate interest owed on a loan from disbursement to repayment, you need the exact day count. In project management, sprint lengths, milestone gaps, and deadline countdowns all depend on an accurate day count. In law and human resources, probation periods, notice periods, and benefit eligibility periods are defined in calendar days.
The years/months/days breakdown shown alongside the total is an approximate calendar expression of the same number. The two values always represent the same duration - one in raw days, one in human-readable calendar units.
Understanding your result
Total days
The exact count of calendar days between the two dates, exclusive of the end date (the standard mathematical convention). This is the primary result and is precise to the day.
Total weeks and remainder
Total days divided by 7, floored to whole weeks, plus any remaining days. Useful for scheduling recurring weekly events, counting pay periods, and any weekly-cycle planning.
Decimal weeks
The exact week count including fractional weeks. 10 days = 1.43 weeks. Useful for proportional calculations - for example, if a weekly salary needs to be prorated for a partial week.
Years, months, days summary
An approximate calendar breakdown of the same duration. Useful for communicating the span in human-friendly terms - "about 2 years and 7 months" - rather than citing a large day count.
Days between dates examples
Example 1 - Project deadline
Start: March 20, 2026 (today) - End: June 30, 2026
March has 31 days: 11 remaining in March, all of April (30), all of May (31), and 30 days in June = 11 + 30 + 31 + 30 = 102 days (14 weeks, 4 days).
Example 2 - Lease duration confirmation
Start: September 1, 2023 - End: September 1, 2024
This one-year span crosses Feb 29, 2024 (leap year). Total = 366 days (52 weeks, 2 days).
Example 3 - Loan interest period
Start: January 15, 2025 - End: July 15, 2025
Jan: 16 remaining + Feb: 28 + Mar: 31 + Apr: 30 + May: 31 + Jun: 30 + Jul: 15 = 181 days (25 weeks, 6 days). A lender would use 181 as the day count for simple interest calculation.
Quick tips for counting days
Common mistakes when counting days between dates
Multiplying years by 365 without checking for leap years
A three-year span from 2020 to 2023 is 366 + 365 + 365 = 1,096 days, not 1,095 - because 2020 was a leap year. Always use exact arithmetic when day-count precision matters.
Using "30 days per month" approximations
A span from January 1 to April 1 is 90 days (31 + 28 + 31 = 90 in a non-leap year), not 90 (3 x 30). The 30-day approximation introduces errors of up to 3 days per month and compounds over longer periods.
Not specifying the inclusive/exclusive convention
From Monday to Friday is 4 days (exclusive end) if you count Mon/Tue/Wed/Thu, but 5 days (inclusive both ends) if you count Mon/Tue/Wed/Thu/Fri. Always clarify with stakeholders which convention applies before using a day count in a contract or schedule.
Assuming a "month" is always 30 or 31 days
February has 28 or 29 days. Any span that includes the end of February will differ from the same nominal span in other months. For exact day counts, always compute from specific calendar dates rather than adding a fixed number of days per month.
By using our dedicated days between dates calculator, you can avoid these manual calculation errors and instantly get an accurate day count for any calendar period.