Convert CDT to IRST
IRST is 8 hours 30 minutes ahead of CDT. CDT is UTC−5 and IRST is UTC+3:30.
Right now: CDT · IRST
Best time to schedule a meeting
Standard 9–5 working hours do not overlap at all between CDT and IRST. Someone has to take an early or late call — or use asynchronous communication instead.
| CDT | IRST | Suitable? |
|---|---|---|
| 9:00 AM | 5:30 PM | outside 9–5 |
| 10:00 AM | 6:30 PM | outside 9–5 |
| 11:00 AM | 7:30 PM | outside 9–5 |
| 12:00 PM | 8:30 PM | outside 9–5 |
| 1:00 PM | 9:30 PM | outside 9–5 |
| 2:00 PM | 10:30 PM | outside 9–5 |
| 3:00 PM | 11:30 PM | outside 9–5 |
| 4:00 PM | 12:30 AM (next day) | outside 9–5 |
| 5:00 PM | 1:30 AM (next day) | outside 9–5 |
CDT to IRST conversion table
| CDT | IRST |
|---|---|
| 12:00 AM | 8:30 AM |
| 1:00 AM | 9:30 AM |
| 2:00 AM | 10:30 AM |
| 3:00 AM | 11:30 AM |
| 4:00 AM | 12:30 PM |
| 5:00 AM | 1:30 PM |
| 6:00 AM | 2:30 PM |
| 7:00 AM | 3:30 PM |
| 8:00 AM | 4:30 PM |
| 9:00 AM | 5:30 PM |
| 10:00 AM | 6:30 PM |
| 11:00 AM | 7:30 PM |
| 12:00 PM | 8:30 PM |
| 1:00 PM | 9:30 PM |
| 2:00 PM | 10:30 PM |
| 3:00 PM | 11:30 PM |
| 4:00 PM | 12:30 AM (next day) |
| 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) |
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.
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.
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 CDT in IRST?
9:00 AM CDT is 5:30 PM IRST.
Is IRST ahead of CDT?
IRST is 8 hours 30 minutes ahead of CDT.
Which time zone does this use?
CDT is UTC−5 and IRST is UTC+3:30. 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.