Days Since Calculator
Count how many days have passed since any historical date or personal milestone. Enter values for instant results with step-by-step formulas.
Reviewed by Abdullah, Technical Content Specialist
Formula
Days = (End Date - Start Date) / 86,400,000 ms/day
The difference in milliseconds between two JavaScript Date objects is divided by 86,400,000 (the number of milliseconds in a 24-hour day) to obtain the number of calendar days. Business days are computed by iterating through each day and excluding Saturdays and Sundays.
Worked Examples
Example 1: Days Since a Birthday
Problem:How many days have passed since January 15, 1990, to March 21, 2026?
Solution:Start date: 1990-01-15\nEnd date: 2026-03-21\nDifference in ms: (2026-03-21) - (1990-01-15) = 1,141,516,800,000 ms\nTotal days = 1,141,516,800,000 / 86,400,000 = 13,214 days\nWeeks = 13,214 / 7 = 1,887 weeks and 5 days\nApprox years = 13,214 / 365.25 = 36.18 years
Result:13,214 days | 1,887 weeks 5 days | ~36.18 years
Example 2: Business Days in a Quarter
Problem:How many business days are there from January 1, 2026 to March 31, 2026?
Solution:Total calendar days: 89\nWeekend days (Sat+Sun): 24\nBusiness days = 89 - 24 = 65\nWeeks = 89 / 7 = 12 weeks and 5 days\nMonths ~ 2.9
Result:89 calendar days | 65 business days | ~12 weeks 5 days
Frequently Asked Questions
How does Days Since Calculator count the number of days between two dates?
Days Since Calculator computes the difference between two dates by converting both dates into milliseconds since January 1, 1970 (the Unix epoch), then subtracting the start date from the end date. The millisecond difference is divided by 86,400,000 (the number of milliseconds in one day) to get the total number of calendar days. It properly handles leap years because the underlying JavaScript Date object accounts for them automatically. You can also choose to include the end day in the count, which adds one extra day to the total, useful when you want to count both the start and end dates as full days.
What is the difference between calendar days and business days?
Calendar days include every single day in the range, whether it falls on a weekday or weekend. Business days, also called working days, only count Monday through Friday and exclude Saturdays and Sundays. For example, a span of 14 calendar days typically contains 10 business days and 4 weekend days. This distinction matters for legal deadlines, shipping estimates, project planning, and payroll calculations. Note that Days Since Calculator does not account for public holidays, which vary by country and region, so the business day count represents a standard working week without holiday adjustments.
How do I calculate the number of working days between two dates?
Count total calendar days, subtract weekends (roughly 2/7 of total days), then subtract any public holidays in the range. For accuracy, iterate through each day and check. Most spreadsheets have NETWORKDAYS functions that handle this automatically.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy