Calcadian Blog
Practical guides to date math, time zones, business days, ISO weeks, Unix timestamps, and fiscal calendars, from the team behind Calcadian.
Calculate hours and minutes between two times, subtract unpaid breaks, handle overnight shifts crossing midnight, and convert to decimal hours for payroll.
How to correctly add 90 days to a date for contracts, notice periods, invoice due dates, and legal deadlines, and the calendar-vs-business-day trap that catches people out.
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.
