Convert IRST to CDT
CDT is 8 hours 30 minutes behind IRST. IRST is UTC+3:30 and CDT is UTC−5.
Right now: IRST · CDT
Best time to schedule a meeting
Standard 9–5 working hours do not overlap at all between IRST and CDT. Someone has to take an early or late call — or use asynchronous communication instead.
| IRST | CDT | Suitable? |
|---|---|---|
| 9:00 AM | 12:30 AM | outside 9–5 |
| 10:00 AM | 1:30 AM | outside 9–5 |
| 11:00 AM | 2:30 AM | outside 9–5 |
| 12:00 PM | 3:30 AM | outside 9–5 |
| 1:00 PM | 4:30 AM | outside 9–5 |
| 2:00 PM | 5:30 AM | outside 9–5 |
| 3:00 PM | 6:30 AM | outside 9–5 |
| 4:00 PM | 7:30 AM | outside 9–5 |
| 5:00 PM | 8:30 AM | outside 9–5 |
IRST to CDT conversion table
| IRST | CDT |
|---|---|
| 12:00 AM | 3:30 PM (previous day) |
| 1:00 AM | 4:30 PM (previous day) |
| 2:00 AM | 5:30 PM (previous day) |
| 3:00 AM | 6:30 PM (previous day) |
| 4:00 AM | 7:30 PM (previous day) |
| 5:00 AM | 8:30 PM (previous day) |
| 6:00 AM | 9:30 PM (previous day) |
| 7:00 AM | 10:30 PM (previous day) |
| 8:00 AM | 11:30 PM (previous day) |
| 9:00 AM | 12:30 AM |
| 10:00 AM | 1:30 AM |
| 11:00 AM | 2:30 AM |
| 12:00 PM | 3:30 AM |
| 1:00 PM | 4:30 AM |
| 2:00 PM | 5:30 AM |
| 3:00 PM | 6:30 AM |
| 4:00 PM | 7:30 AM |
| 5:00 PM | 8:30 AM |
| 6:00 PM | 9:30 AM |
| 7:00 PM | 10:30 AM |
| 8:00 PM | 11:30 AM |
| 9:00 PM | 12:30 PM |
| 10:00 PM | 1:30 PM |
| 11:00 PM | 2:30 PM |
About IRST
Iran Standard Time (IRST) is UTC+3:30. It is used in Iran, all year.
Iran Standard Time is UTC+3:30. Iran ran daylight saving for decades and stopped in 2022, so material written before then puts the country half an hour further ahead in summer and is now wrong. Half-hour offsets are rare enough that scheduling tools sometimes round them, which turns a correct calculation into a thirty-minute error.
About CDT
Central Daylight Time (CDT) is UTC−5. It is used in Chicago, Dallas and Houston from March to November.
Central Daylight Time is UTC−5, the summer clock for Chicago, Dallas and Houston, from the second Sunday in March to the first Sunday in November. Mexico is the complication: it abolished daylight saving nationally in 2022, so Mexico City stays on UTC−6 all year and is now an hour behind Chicago for eight months of the year rather than matching it.
Does this gap change with the seasons?
This gap is seasonal. The abbreviations themselves are fixed offsets, but the region on CDT switches to CST (UTC−6) from November to March. So the 8.5-hour figure on this page is correct for the part of the year when both places are actually on these abbreviations, and changes by an hour outside it.
IRST does not shift, so the whole change comes from one side. A recurring meeting fixed in IRST will appear to move by an hour for everyone on the other side, twice a year, without anyone changing anything.
This is the reason scheduling systems store an IANA zone such as Region/City rather than an offset or an abbreviation: the zone knows its own rules and the offset does not.
Frequently asked questions
What time is 9:00 AM IRST in CDT?
9:00 AM IRST is 12:30 AM CDT.
Is CDT ahead of IRST?
CDT is 8 hours 30 minutes behind IRST.
Which time zone does this use?
IRST is UTC+3:30 and CDT is UTC−5. Both abbreviations denote a single fixed offset, so this conversion never shifts with daylight saving — what changes is which abbreviation a place is using at the time.