CT to IRST Time Converter

Common Times Converted

CT on the left, IRST on the right.

CT to IRST: Full 24-Hour Conversion Table

Shaded rows are working hours; the darker shade marks the hours when both zones are at work.

What CT and IRST Actually Are

CT — Central Time

Chicago, Houston, Dallas, Mexico City, Winnipeg. Standing at UTC-6:00 as written, and the region does change its clocks, so its live offset moves by an hour twice a year. The next change is on Sunday, November 1, 2026, to CST.

Central Time is the widest US zone by land area, stretching from the Gulf coast to the Canadian border, and it also covers Mexico City.

IRST — Iran Standard Time

Tehran, Mashhad, Isfahan. Standing at UTC+3:30 as written, and the region does not change its clocks, so that offset holds all year. Iran abolished daylight saving in 2022, so the half-hour offset now holds all year.

Iran abolished daylight saving in 2022. Its half-hour offset is a deliberate compromise between the solar times of its western and eastern borders.

What This Means in Practice

Expect times on the half hour

IRST sits on a 30-minute offset rather than a whole hour, so a round number on one side is never a round number on the other. A 9:00 meeting becomes 30 minutes past the hour, which is exactly the detail calendar invitations get wrong when someone converts in their head.

The date changes mid-working-day

For 1 of the eight hours in a normal CT working day, the equivalent IRST time falls on a different calendar date. Anything scheduled in that stretch needs the date checked as well as the time, or a Tuesday call quietly becomes a Wednesday one at the other end.

This gap is not fixed

CT changes its clocks and IRST does not, so the difference between them moves by an hour twice a year. A recurring meeting set now will drift for one side from Sunday, November 1, 2026 unless someone resets it.

Major Cities in Each Zone

Cities on CT

Cities on IRST