Time Zones and Date Math: Avoiding the Off-by-One-Day Bug
Why a date that looks right in one time zone is wrong in another, and the simple rule that fixes most date-math bugs in software.
Calcadian Blog
Practical guides to date math, time zones, business days, ISO weeks, Unix timestamps, and fiscal calendars, from the team behind Calcadian.
Why a date that looks right in one time zone is wrong in another, and the simple rule that fixes most date-math bugs in software.
The right way to compute exact age from a date of birth, including the leap-year edge case that breaks naive subtraction.
Unix timestamps count seconds since 1970-01-01 UTC. Here's what that means, why it was chosen, and how to convert to and from human-readable dates.
Fiscal years aren't always 365 days. Here's how US federal, UK, and corporate 52/53-week fiscal years work, and how to count their days correctly.
ISO 8601 week numbers and US week numbers disagree by up to a full week. Here's why, and how to know which one your tools use.
A clear method for counting working days between two dates, with weekend handling, US/UK/EU holiday rules, and Excel/Sheets equivalents.