Date Calculator
Add or subtract business and calendar days, find durations between dates, and identify leap years.
Parameters & Inputs
Summary & Breakdown
Calendar Detail
About the Date Calculator
Calendar arithmetic is complicated by irregular month lengths, leap year Februarys, and business workweeks that exclude Saturdays and Sundays.
This date utility operates in two modes: finding the exact calendar and business day gap between two chosen dates, or adding/subtracting days, weeks, months, or years forward or backward.
Ideal for calculating loan maturities, project sprint milestones, court deadlines, and vacation countdowns.
How the Calculations Work
Computes millisecond duration between timestamps, tallies weekend days (Saturdays and Sundays), and offsets calendar dates via JavaScript UTC date components.
Days = (Date2 - Date1) / 86,400,000 ms | Business Days = Total Days - Weekends
Variables & Definitions
- Date 1 & Date 2: Start and end calendar dates
- Business Days: Standard Monday through Friday workdays
- Calendar Days: Every 24-hour solar day inclusive
Between October 1 and November 15: Exactly 45 calendar days elapse. Excluding 13 Saturday/Sunday weekend days leaves 32 business working days.
Key Terms Explained
Business Days
Working days excluding weekends (Saturday and Sunday) and statutory public bank holidays.
Julian Day Number
The continuous count of days since the beginning of the Julian period used by astronomers.
ISO 8601
The international standard for date formatting (YYYY-MM-DD).
Daylight Saving Time (DST)
Clock shifts that produce 23-hour or 25-hour days twice a year.
Practical Tips & Pitfalls to Avoid
Check business day assumptions
Statutory public holidays vary by jurisdiction and are not automatically deducted from business days.
Count inclusive or exclusive
Standard date difference counts elapsed intervals (if today is Monday and tomorrow is Tuesday, difference is 1 day).
Adding months on the 31st
Adding one month to January 31 lands on February 28 (or 29 in leap years).
Calculate project sprints
Add 14 days or 2 weeks to your kickoff date to find exact two-week sprint deadlines.
Frequently Asked Questions
A common 365-day year contains 260 or 261 weekdays (Monday through Friday), depending on which day of the week January 1 falls on.
It excludes weekends (Saturday and Sunday). National and bank holidays depend on specific country and state calendars.
A leap year contains 366 days instead of the standard 365, adding February 29th.
Century years (1800, 1900, 2100) are not leap years unless they are evenly divisible by 400 (like 1600, 2000, 2400).
When adding a month to an end-of-month date where the destination month is shorter, the date snaps to the last day of that shorter month.