IRST to Chicago
-8h 30mIRST
IRSTSOURCEChicago
CDTGreen rows indicate typical business hours (9 AM - 5 PM)
IRST and CDT on the World Map
The map below highlights the IRST (Iran Standard Time) and CDT (Central Standard Time) timezone regions across the globe.
IRST – Iran Standard Time
UTC+03:30Iran Standard Time (IRST) is the time zone for Iran, 3 hours and 30 minutes ahead of UTC.
- •IRST is one of only a few time zones with a 30-minute offset.
- •Iran observes daylight saving time, switching to IRDT (UTC+04:30).
- •Tehran has a metropolitan population of over 16 million.
CST – Central Standard Time
UTC-06:00Central Standard Time (CST) is the time zone for the central United States, Canada, and Mexico, 6 hours behind UTC.
- •CST covers 20 US states fully or partially.
- •Chicago and Houston are the two largest cities in the Central Time Zone.
- •Mexico City, one of the world's most populous cities, operates on CST.
- •CST is 1 hour behind EST and 2 hours ahead of PST.
About Chicago
WikipediaChicago operates on Central Time (CST/CDT), 1 hour behind New York. Home to CME and CBOE, Chicago is a global center for derivatives trading.
The Chicago Board of Trade is the world's oldest futures and options exchange.
Time Conversion Guide: IRST to Chicago
IRST runs on Iran Standard Time (IRST) at UTC+03:30. Chicago runs on Central Daylight Time (CDT) at UTC-05:00, also currently on daylight saving time. That puts IRST 8 hours 30 minutes behind Chicago — a difference of -8h 30m at the current offsets.
In practice, when it is 9:00 AM in IRST it is 12:30 AM in Chicago. Midnight in IRST is 3:30 PM in Chicago.Chicago observes daylight saving time while IRST does not, so the gap narrows or widens by an hour part of the year.
IRST to Chicago time conversion table
| IRST (IRST) | Chicago (CDT) | Day |
|---|---|---|
| 12:00 AM | 3:30 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 | same day |
| 12:00 PM | 3:30 AM | same day |
| 3:00 PM | 6:30 AM | same day |
| 5:00 PM | 8:30 AM | same day |
| 6:00 PM | 9:30 AM | same day |
| 9:00 PM | 12:30 PM | same day |
Why people convert IRST to Chicago time
- Scheduling a call from IRST to Chicago: a 10:00 AM start in IRST lands at 1:30 AM in Chicago, so you can confirm the slot without doing the arithmetic yourself.
- Handling a -8h 30m gap: IRST and Chicago have no overlap inside a normal 9-to-5 day, so real-time meetings need an early-morning or late-evening slot on one side. 9:00 AM in Chicago is 12:30 AM in IRST.
- Coordinating a IRST-based team with Chicago contacts: quoting times in the other side's local clock — not your own — removes the single biggest source of missed meetings.
- Always state the zone abbreviation, not just the hour. "3:00 PM IRST" is unambiguous; "3 PM" across a -8h 30m gap is not.
- With a -8h 30m gap there is no shared 9-to-5 window, so alternate the early start: one week IRST takes the early slot, the next week Chicago does.
- Chicago: Clocks fall back on Sun, Nov 1, 2026. Any meeting series spanning that date will shift by an hour in local time.
About IRST (Iran Standard Time)
Iran Standard Time (IRST) is one of the few time zones with a 30-minute offset. Iran observes daylight saving time (IRDT, UTC+04:30) from late March to late September. Tehran, the capital, is one of the largest cities in the Middle East.
About CST (Central Standard Time)
Central Standard Time (CST) covers the central region of North America. It is the second most populous time zone in the US, including major cities like Chicago, Houston, and Dallas. CST is also used in Mexico City and much of Central America including Guatemala, Honduras, El Salvador, and Costa Rica. During summer, most of the US and Canada switch to Central Daylight Time (CDT, UTC-05:00), while Mexico and Central American countries generally remain on CST.
Best time to call between IRST and Chicago
With a -8h 30m offset there is no overlap inside a normal 9 AM – 5 PM day. Chicago opens at 9:00 AM CDT, which is 12:30 AM in IRST, so real-time calls need an early-morning or late-evening slot on one side.
Business hours overlap
IRST and Chicago have no shared working hours because of the -8h 30m gap. Teams need to alternate early starts or rely on asynchronous handovers.
IRST is 8 hours 30 minutes behind Chicago (IRST UTC+03:30 → CDT UTC-05:00). There is no shared 9-to-5 window, so plan around an early or late slot. Remember to re-check around daylight-saving transitions.
🕐 Daylight Saving Time Info
IRST
Does not observe DST
Chicago
☀ Currently in DST
Standard: UTC-06:00 · DST: UTC-05:00
Clocks fall back on Sun, Nov 1, 2026
Learn More About Time
Dive deeper into the fascinating world of timekeeping, time zones, and how they shape our global society:
Frequently Asked Questions
What is the time difference between IRST and Chicago?
IRST (IRST, UTC+03:30) is 8 hours 30 minutes behind Chicago (CDT, UTC-05:00). The gap is currently -8h 30m.
How do I convert IRST time to Chicago time?
Add -8h 30m to IRST local time. For example, 9:00 AM in IRST is 12:30 AM in Chicago.
What time is it in Chicago right now?
Chicago uses CDT at UTC-05:00. Use the live converter at the top of this page — it updates in real time and already accounts for the -8h 30m offset from IRST.
What is the best time to call Chicago from IRST?
There is no shared working-hours window because of the -8h 30m gap. The closest option is 1:00 PM in IRST, which is 4:30 AM in Chicago.
Which is behind, IRST or Chicago?
IRST is 8 hours 30 minutes behind Chicago. When it is 12:00 PM in IRST it is 3:30 AM in Chicago.
Do IRST and Chicago use different time zones?
IRST uses IRST at UTC+03:30, while Chicago (USA) uses CDT at UTC-05:00. The IANA identifiers are Asia/Tehran and America/Chicago.
Does daylight saving time affect the IRST–Chicago difference?
Yes at the moment: Chicago is on daylight saving time and IRST is not, so the -8h 30m gap shifts by an hour when exactly one of them changes clocks.
Which other cities share IRST's time zone?
IRST also covers Tehran, Isfahan, Mashhad, Tabriz, Shiraz, Karaj.
Which countries use IRST, IRST's zone?
IRST is used in Iran.
Is there a day difference between IRST and Chicago?
Not normally. The -8h 30m gap only pushes the date over the previous day.
What is the time difference between IRST and Chicago?
Chicago is -8h 30m from IRST.
What timezone is IRST in?
IRST operates on its local timezone.
What timezone is Chicago in?
Chicago operates on Central Time (CST/CDT), 1 hour behind New York. Home to CME and CBOE, Chicago is a global center for derivatives trading.
What are the business hours in Chicago?
Standard business hours in Chicago are 8:00 AM - 5:00 PM CST.
Which countries use IRST (Iran Standard Time)?
IRST is used in Iran.
Does IRST observe daylight saving time?
Yes, IRST switches to IRDT during summer months.
What are some interesting facts about IRST?
IRST is one of only a few time zones with a 30-minute offset. Iran observes daylight saving time, switching to IRDT (UTC+04:30).
Which cities are in the CST timezone?
Major cities in the CST timezone include Chicago, Houston, Dallas, San Antonio, Mexico City, Austin, Winnipeg, Memphis.
What is the UTC offset for CST?
Central Standard Time (CST) is at UTC-06:00. During daylight saving time, it shifts to CDT.
What should I know about the CST timezone?
CST covers 20 US states fully or partially. Chicago and Houston are the two largest cities in the Central Time Zone.
When is it midnight in IRST, what time is it in Chicago?
When it is 12:00 AM (midnight) in IRST (IRST), it is -8h 30m later in Chicago (CST).
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