Date & Duration Calculator

The calculator computes duration by converting both dates to UTC timestamps and finding the absolute difference in milliseconds. This value is then divided by 86,400,000 (the number of milliseconds in a standard day: 24 hours * 60 minutes * 60 seconds * 1,000 milliseconds). You can choose whether to include or exclude the start date in the final count.

Our calculation engine relies on the standard Gregorian calendar system. It automatically accounts for leap years (years divisible by 4, except for century years not divisible by 400) by assigning 29 days to February. It also handles variable month lengths (28, 30, or 31 days) to ensure precise year-month-day breakdowns.

Calendar days represent the total elapsed time between two dates without any exclusions. Business days exclude weekends (Saturdays and Sundays) and can optionally exclude U.S. federal holidays. This is calculated using the formula: Business Days = Calendar Days - Weekend Days - Holidays.

To calculate a future date by adding business days, select the 'Add / Subtract Date' tab, choose 'Add (+)', set the delta type to 'Business Days', and input 45. The engine will start from your reference date and step forward day-by-day, skipping Saturdays, Sundays, and federal holidays until it reaches the 45th business day.

No. All date calculations, calendar generation, and holiday shifts are performed client-side using JavaScript in your web browser. None of your date entries, holiday requests, or calculated time spans are sent to a server, ensuring 100% data privacy.