Building a Work-Hours Calculator? Time Arithmetic Is the Trap
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If you have ever built a timesheet tool, a shift planner, or a payroll helper, you know the feature looks trivial until you write the first test. Start time minus end time, minus a break, times an hourly rate. What could go wrong? Plenty — and almost all of it comes from treating time like ordinary decimal numbers. This article walks through the four traps that bite every work-hours calculator, with the validation cases I use to check them. The examples are in JavaScript, but the lessons apply