How to Convert Between Time Zones Using UTC Offsets
Skip the guesswork: convert the local time to UTC, then to the target zone. Includes half-hour offsets, date changes and a worked meeting-overlap example.
Time & Dates
Durations, time zones, working days and clock formats made simple.
12-Hour to 24-Hour Time: Conversion Rules and Common Slips
Two rules cover every conversion between AM/PM and the 24-hour clock. Here they are, with a reference table, midnight and noon explained, and the usual mistakes.
Daylight Saving Time: Why Some Days Have 23 or 25 Hours
When clocks change, a local day is no longer 24 hours. Learn what shifts, how it alters durations and meeting times, and how to calculate safely.
How to Find the Day of the Week for Any Date in Your Head
The doomsday method turns weekday-finding into a few small sums. Learn the anchor dates, the century table and two worked examples you can check.
How to Calculate Age From a Date of Birth by Hand
Subtracting years is only half the job. Here is the borrow method for an exact age, a way to check it in days, and what happens to 29 February birthdays.
How to Calculate Hours Between Two Times, Even Overnight
Time subtraction trips people up because minutes run to 60 and a shift can cross midnight. Here is a reliable method, with a break deducted and a flight example.
How to Count the Days Between Two Dates (and Avoid Off-by-One)
Counting days between dates is simple once you decide whether both end dates count. This guide covers the day-of-year method, year boundaries and leap days.
How to Count Working Days Between Two Dates
Working days are weekdays minus holidays. Learn the weeks-times-five shortcut, how to decide whether the start day counts, and how to add working days to a date.
Leap Year Rules Explained: Why 1900 Was Not but 2000 Was
Every fourth year is a leap year, except when it is not. Learn the full three-part rule, the reason behind it and a formula for counting leap years.
Converting Minutes to Decimal Hours for Timesheets and Pay
Pay is calculated in decimal hours, but clocks run in base 60. Learn the conversion, a quick reference table, and why rounding each shift can shave off pay.