CST to IRST Time Converter
IRST is 8 hours and 30 minutes ahead of CST. The US Central states are currently on CDT (UTC-5:00), and IRST is UTC+3:30.
Best Time to Call Between CST and IRST
Standard 9-to-5 hours in these two zones never overlap, so someone has to take the call outside their working day. The most workable window is 7:00 AM to 2:00 PM CST, which is 3:30 PM to 10:30 PM IRST.
both at work CST only IRST only neither — hours along the strip are CST.
Common Times Converted
CST on the left, IRST on the right.
CST to IRST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| CST | IRST | Working hours |
|---|---|---|
| 12:00 AM | 8:30 AM | — |
| 1:00 AM | 9:30 AM | IRST only |
| 2:00 AM | 10:30 AM | IRST only |
| 3:00 AM | 11:30 AM | IRST only |
| 4:00 AM | 12:30 PM | IRST only |
| 5:00 AM | 1:30 PM | IRST only |
| 6:00 AM | 2:30 PM | IRST only |
| 7:00 AM | 3:30 PM | IRST only |
| 8:00 AM | 4:30 PM | IRST only |
| 9:00 AM | 5:30 PM | CST only |
| 10:00 AM | 6:30 PM | CST only |
| 11:00 AM | 7:30 PM | CST only |
| 12:00 PM | 8:30 PM | CST only |
| 1:00 PM | 9:30 PM | CST only |
| 2:00 PM | 10:30 PM | CST only |
| 3:00 PM | 11:30 PM | CST only |
| 4:00 PM | 12:30 AM next day | CST only |
| 5:00 PM | 1:30 AM next day | — |
| 6:00 PM | 2:30 AM next day | — |
| 7:00 PM | 3:30 AM next day | — |
| 8:00 PM | 4:30 AM next day | — |
| 9:00 PM | 5:30 AM next day | — |
| 10:00 PM | 6:30 AM next day | — |
| 11:00 PM | 7:30 AM next day | — |
What CST and IRST Actually Are
CST — Central Standard 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. CST also stands for China Standard Time (UTC+8) and Cuba Standard Time (UTC-5). This page covers the North American one.
Saskatchewan sits inside the Central zone but never changes its clocks, so it matches CST in winter and its neighbors' MDT in summer.
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 CST 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
CST 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 CST
Cities on IRST
Frequently Asked Questions
What is the time difference between CST and IRST?
IRST is 8 hours and 30 minutes ahead of CST. That is the live figure. Taken strictly as written, the gap between CST and IRST is 9 hours and 30 minutes — the two differ because at least one of these regions is currently on daylight saving.
What is 9:00 AM CST in IRST?
9:00 AM CST is 5:30 PM IRST.
What are the best hours to schedule a call between CST and IRST?
Standard business hours in these two zones do not overlap at all, so one side has to work outside the 9-to-5. The most workable window is 7:00 AM to 2:00 PM CST, which is 3:30 PM to 10:30 PM IRST.
Does the difference between CST and IRST change during the year?
Yes. CST observes daylight saving and IRST does not, so the gap shifts by an hour at least twice a year. The next clock change is on Sunday, November 1, 2026.
Does CST always mean Central Standard Time?
CST also stands for China Standard Time (UTC+8) and Cuba Standard Time (UTC-5). This page covers the North American one.
Does IRST always mean Iran Standard Time?
Iran abolished daylight saving in 2022, so the half-hour offset now holds all year.