IRST to CST Time Converter
CST is 8 hours and 30 minutes behind IRST. IRST is UTC+3:30, and The US Central states are currently on CDT (UTC-5:00).
Best Time to Call Between IRST and CST
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 4:00 PM to 10:00 PM IRST, which is 7:30 AM to 1:30 PM CST.
both at work IRST only CST only neither — hours along the strip are IRST.
Common Times Converted
IRST on the left, CST on the right.
IRST to CST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| IRST | CST | Working hours |
|---|---|---|
| 12:00 AM | 3:30 PM prev day | CST only |
| 1:00 AM | 4:30 PM prev day | CST only |
| 2:00 AM | 5:30 PM prev day | — |
| 3:00 AM | 6:30 PM prev day | — |
| 4:00 AM | 7:30 PM prev day | — |
| 5:00 AM | 8:30 PM prev day | — |
| 6:00 AM | 9:30 PM prev day | — |
| 7:00 AM | 10:30 PM prev day | — |
| 8:00 AM | 11:30 PM prev day | — |
| 9:00 AM | 12:30 AM | IRST only |
| 10:00 AM | 1:30 AM | IRST only |
| 11:00 AM | 2:30 AM | IRST only |
| 12:00 PM | 3:30 AM | IRST only |
| 1:00 PM | 4:30 AM | IRST only |
| 2:00 PM | 5:30 AM | IRST only |
| 3:00 PM | 6:30 AM | IRST only |
| 4:00 PM | 7:30 AM | IRST only |
| 5:00 PM | 8:30 AM | — |
| 6:00 PM | 9:30 AM | CST only |
| 7:00 PM | 10:30 AM | CST only |
| 8:00 PM | 11:30 AM | CST only |
| 9:00 PM | 12:30 PM | CST only |
| 10:00 PM | 1:30 PM | CST only |
| 11:00 PM | 2:30 PM | CST only |
What IRST and CST Actually Are
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.
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.
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.
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 IRST
Cities on CST
Frequently Asked Questions
What is the time difference between IRST and CST?
CST is 8 hours and 30 minutes behind IRST. That is the live figure. Taken strictly as written, the gap between IRST and CST 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 IRST in CST?
9:00 AM IRST is 12:30 AM CST.
What are the best hours to schedule a call between IRST and CST?
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 4:00 PM to 10:00 PM IRST, which is 7:30 AM to 1:30 PM CST.
Does the difference between IRST and CST 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 IRST always mean Iran Standard Time?
Iran abolished daylight saving in 2022, so the half-hour offset now holds all year.
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.