FreeTools Labs Glossary
Dates, time and working hours
Learn how calendar and time differences are calculated, and why months, years and working spans cannot always be treated as fixed quantities.
Relevant tool
Date & Time Calculator
Calculate dates, ISO weeks, workdays, clock times, durations and working time.
Open Date & Time Calculator →Date and time tasks use calendar rules, clock intervals and entered work periods; a date difference is not the same operation as a duration that crosses midnight.
Functions and inputs
Eleven paths cover date difference, date shifting, calendar information, weekdays, time difference, time shifting, duration arithmetic, decimal hours, daily work time, intervals and weekly work time.
Calculation model
The modes turn the chosen calendar or clock relationship into weeks, remaining days, weekdays or elapsed time: weeks = floor(days ÷ 7); remaining days = days mod 7; weekdays = Mon–Fri.
How the calculator model works
Date-only differences use calendar dates; weekday counting includes both endpoints and counts Monday to Friday only. Time-only differences crossing midnight require the explicit next-day option. Daily and weekly work-time paths add entered values mathematically and do not infer breaks or employment rules.
Checked examples
These checked cases cover a date interval, a leap-day shift and an overnight clock interval: 2026-01-01 → 2026-01-11 = 10 d = 1 w + 3 d; 2026-03-29 → 2026-03-30 = 1 d; 2028-01-31 + 1 month = 2028-02-29; 23:00 → 01:00 (+1 d) = 2:00.
Units, display and interpretation
Calendar dates, ISO weeks, clock notation and decimal hours remain distinct displays so that the chosen mode is clear: calendar days · complete weeks/remainder · ISO week · HH:MM(:SS) · decimal hours.
Scope and limits
There is no timezone conversion, public-holiday database or employment-law assessment. Calendar and work-time results are limited to the entered dates, times, pauses, intervals and target hours.