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.
5 min readtime zones, developers
Calcadian Blog
Guides to date & time calculation
Practical guides to date math, time zones, business days, ISO weeks, Unix timestamps, and fiscal calendars, from the team behind Calcadian.
How to Calculate Age in Years, Months, and Days
The right way to compute exact age from a date of birth, including the leap-year edge case that breaks naive subtraction.
4 min readage, how-toWhat Is a Unix Timestamp, and Why Does It Start in 1970?
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.
4 min readunix, timestampsHow Many Days Are in a Fiscal Year?
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.
5 min readfiscal year, accountingISO Week vs US Week Numbering: What's the Difference?
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.
5 min readiso week, calendarHow to Count Business Days Between Two Dates (Excluding Holidays)
A clear method for counting working days between two dates, with weekend handling, US/UK/EU holiday rules, and Excel/Sheets equivalents.
6 min readbusiness days, how-to