What date is 06/07/2026?
If you're American, it's the 7th of June. If you're British, it's the 6th of July. Both readers are completely sure of their answer, and neither of them will think to question it. That's what makes date bugs so nasty. Nothing looks broken. Someone just turns up a month early.
At Helm Tickets, this mattered a lot. The whole point of a ticketing system is organising events on dates, so when we expanded into the US, getting date formats right wasn't a nice extra. A ticket with the wrong date on it is a ticket for the wrong event.
This chapter covers how to show dates and times so people read them correctly, how to store them so they stay correct, and the timezone problems that sit underneath both.