Isfahan stays on Iran Standard Time at UTC+03:30 every day of the year. There is no spring-forward or fall-back here, which puts it with the majority: most of the world's time zones do not observe daylight saving.

That sounds like it makes scheduling simpler, and locally it does — but it introduces a different trap for anyone working with Isfahan from a country that does change clocks. The offset between you and Isfahan is not constant: it changes when your clocks move, even though nothing changed here. A recurring call that has run at the same local time for months will shift by an hour, from your side, without anyone editing the invite.

Most time zones sit a whole number of hours from UTC. Isfahan does not: it runs at UTC+03:30, offset by 30 minutes from the nearest whole hour. Only a handful of the world's zones do this.

It matters more than it sounds. Mental arithmetic that works everywhere else quietly fails here, and some scheduling tools round to the nearest hour — which puts a meeting in the wrong place by 30 minutes. If you are coordinating with Isfahan, read the offset rather than estimating it.

The difference between two cities is not a constant. It changes whenever either side moves its clocks — and because regions switch on different dates, there are short windows each year when the usual gap is wrong. These are the dates that matter for Isfahan: