About

Accurate time tracking drives efficient project management, legal compliance, and supply chain logistics. Errors in calculating durations lead to missed deadlines or breach of contract penalties. This tool determines the exact time delta between two specific timestamps. It handles standard calendar days and business days, accounting for leap years and specific exclusions. Use this for verifying invoices, planning sprints, or determining statute of limitations expirations.

Formulas

The core calculation relies on converting timestamps to Coordinated Universal Time (UTC) milliseconds to avoid timezone variance.

Δt = |Datet_end − Datet_start|

To convert milliseconds to days:

Days = Δt1000 × 60 × 60 × 24

Reference Data

Time Unit	Conversion Factor (Approx)	Standard Definition
Gregorian Year	365.2425 days	Average length accounting for leap years
Business Month	21.74 days	Average working days per month (5-day week)
Common Year	365 days	52 weeks + 1 day
Leap Year	366 days	Occurs every 4 years (mostly)
Fortnight	14 days	Two weeks
Quarter	91.31 days	1/4 of a solar year
Olympiad	1,461 days	Four-year period
Sidereal Day	23h 56m 4s	Earth's rotation relative to stars

Frequently Asked Questions

Most legal and project management standards calculate "duration" as the difference, meaning the end date is exclusive (T2 - T1). However, for inclusive counts (e.g., "Day 1 to Day 3" is 3 days), select the "Include End Date" option in the settings.

Business day logic strictly excludes Saturdays and Sundays. The tool iterates through the date range, checking the day index (0 for Sunday, 6 for Saturday). Optional holiday databases can be applied to subtract federal or bank holidays.

Leap years introduce a 366th day (February 29). Simple subtraction often ignores this if using fixed 365-day math. This tool uses native UTC timestamps, which inherently account for the extra 24 hours in leap years.

The tool supports the ECMAScript Date object range, approximately ±100,000,000 days relative to January 1, 1970. This covers all practical historical and future logistics needs.