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Chicago to IRST

+8h 30m

Chicago

CDTSOURCE
USA · UTC-05:00☀ DST active
HH12
:
MM00
  
12:00 (24-hr)
12 AM6 AM12 PM6 PM12 AM

IRST

IRST
UTC+03:30
HH08
:
MM30
  
20:30 (24-hr)
12 AM6 AM12 PM6 PM12 AM
Chicago
IRST
12:00 AM
8:30 AM
2:00 AM
10:30 AM
4:00 AM
12:30 PM
6:00 AM
2:30 PM
8:00 AM
4:30 PM
10:00 AM
6:30 PM
12:00 PM
8:30 PM
2:00 PM
10:30 PM
4:00 PM
12:30 AM+1
6:00 PM
2:30 AM+1
8:00 PM
4:30 AM+1
10:00 PM
6:30 AM+1

Green rows indicate typical business hours (9 AM - 5 PM)

CDT and IRST on the World Map

The map below highlights the CDT (Central Standard Time) and IRST (Iran Standard Time) timezone regions across the globe.

CDTIRSTChicagoHoustonDallasSan AntonioTehranIsfahanMashhadTabriz
CDT Zone
→
IRST Zone

Explore all world timezones interactively →

CST – Central Standard Time

UTC-06:00

Central Standard Time (CST) is the time zone for the central United States, Canada, and Mexico, 6 hours behind UTC.

Countries in CST
United States (Central)Canada (Manitoba, Saskatchewan)MexicoGuatemalaHondurasEl SalvadorCosta RicaNicaraguaBelize
Major Cities in CST
ChicagoHoustonDallasSan AntonioMexico CityAustinWinnipegMemphisMilwaukeeNashvilleKansas CityNew OrleansMinneapolisGuatemala City
Key Facts about CST
  • •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.
Daylight Saving:Yes – switches to CDT
Learn more about CST on Wikipedia

IRST – Iran Standard Time

UTC+03:30

Iran Standard Time (IRST) is the time zone for Iran, 3 hours and 30 minutes ahead of UTC.

Countries in IRST
Iran
Major Cities in IRST
TehranIsfahanMashhadTabrizShirazKaraj
Key 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).
  • •Tehran has a metropolitan population of over 16 million.
Daylight Saving:Yes – switches to IRDT
Learn more about IRST on Wikipedia

About Chicago

Wikipedia

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.

Population:2.7 million
Metro:9.5 million
Business Hours:8:00 AM - 5:00 PM CST
Currency:USD ($)
Stock Exchange:CME (Chicago Mercantile Exchange), CBOE
Key Landmarks
Willis TowerMillennium ParkCloud Gate (The Bean)Navy PierArt Institute of Chicago
Did You Know?

The Chicago Board of Trade is the world's oldest futures and options exchange.

Learn more about CDT timezone →

Understanding the +8h 30m Gap: Chicago vs IRST

Chicago runs on Central Daylight Time (CDT) at UTC-05:00, currently observing daylight saving time. IRST runs on Iran Standard Time (IRST) at UTC+03:30. That puts Chicago 8 hours 30 minutes ahead of IRST — a difference of +8h 30m at the current offsets.

In practice, when it is 9:00 AM in Chicago it is 5:30 PM in IRST. Midnight in Chicago is 8:30 AM in IRST.Chicago observes daylight saving time while IRST does not, so the gap narrows or widens by an hour part of the year.

Chicago to IRST time conversion table

Chicago (CDT)IRST (IRST)Day
12:00 AM8:30 AMsame day
6:00 AM2:30 PMsame day
7:00 AM3:30 PMsame day
8:00 AM4:30 PMsame day
9:00 AM5:30 PMsame day
12:00 PM8:30 PMsame day
3:00 PM11:30 PMsame day
5:00 PM1:30 AMnext day
6:00 PM2:30 AMnext day
9:00 PM5:30 AMnext day

Why people convert Chicago to IRST time

  • Scheduling a call from Chicago to IRST: a 10:00 AM start in Chicago lands at 6:30 PM in IRST, so you can confirm the slot without doing the arithmetic yourself.
  • Handling a +8h 30m gap: Chicago and IRST 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 IRST is 5:30 PM in Chicago.
  • Keeping family and friends in sync: knowing that 8:00 PM in Chicago is 4:30 AM in IRST makes it easy to avoid calling at 3 AM.
  • Always state the zone abbreviation, not just the hour. "3:00 PM CDT" 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 Chicago takes the early slot, the next week IRST does.
  • Chicago: Clocks fall back on Sun, Nov 1, 2026. Re-check this page after that date because the offset changes and so does the +8h 30m gap.

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.

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.

Best time to call between Chicago and IRST

With a +8h 30m offset there is no overlap inside a normal 9 AM – 5 PM day. IRST opens at 9:00 AM IRST, which is 5:30 PM in Chicago, so real-time calls need an early-morning or late-evening slot on one side.

Business hours overlap

Chicago and IRST have no shared working hours because of the +8h 30m gap. Teams need to alternate early starts or rely on asynchronous handovers.

Chicago is 8 hours 30 minutes ahead of IRST (CDT UTC-05:00 → IRST UTC+03:30). 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

Chicago

☀ Currently in DST

Standard: UTC-06:00 · DST: UTC-05:00

Clocks fall back on Sun, Nov 1, 2026

IRST

Does not observe DST

Learn More About Time

Dive deeper into the fascinating world of timekeeping, time zones, and how they shape our global society:

⏳
History of Timekeeping
From sundials to atomic clocks - 5000 years of measuring time
🌍
How Time Zones Work
UTC, offsets, and why zones don't follow straight lines
☀️
Daylight Saving Time
DST dates, which countries observe it, and the ongoing debate

Frequently Asked Questions

What is the time difference between Chicago and IRST?

Chicago (CDT, UTC-05:00) is 8 hours 30 minutes ahead of IRST (IRST, UTC+03:30). The gap is currently +8h 30m.

How do I convert Chicago time to IRST time?

Add +8h 30m to Chicago local time. For example, 9:00 AM in Chicago is 5:30 PM in IRST.

What time is it in IRST right now?

IRST uses IRST at UTC+03:30. Use the live converter at the top of this page — it updates in real time and already accounts for the +8h 30m offset from Chicago.

What is the best time to call IRST from Chicago?

There is no shared working-hours window because of the +8h 30m gap. The closest option is 1:00 PM in Chicago, which is 9:30 PM in IRST.

Which is ahead, Chicago or IRST?

Chicago is 8 hours 30 minutes ahead of IRST. When it is 12:00 PM in Chicago it is 8:30 PM in IRST.

Do Chicago and IRST use different time zones?

Chicago (USA) uses CDT at UTC-05:00, while IRST uses IRST at UTC+03:30. The IANA identifiers are America/Chicago and Asia/Tehran.

Does daylight saving time affect the Chicago–IRST 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 Chicago's time zone?

CDT also covers Chicago, Houston, Dallas, San Antonio, Mexico City, Austin, Winnipeg, Memphis and 6 more.

Which countries use CDT, Chicago's zone?

CDT is used in United States (Central), Canada (Manitoba, Saskatchewan), Mexico, Guatemala, Honduras, El Salvador, Costa Rica, Nicaragua and 1 more.

Is there a day difference between Chicago and IRST?

Not normally. The +8h 30m gap only pushes the date over for late-evening times.

What is the time difference between Chicago and IRST?

IRST is +8h 30m from Chicago.

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 timezone is IRST in?

IRST operates on its local timezone.

What are the business hours in Chicago?

Standard business hours in Chicago are 8:00 AM - 5:00 PM CST.

Which countries use CST (Central Standard Time)?

CST is used in United States (Central), Canada (Manitoba, Saskatchewan), Mexico, Guatemala, Honduras, El Salvador, and 3 more countries.

Does CST observe daylight saving time?

Yes, CST switches to CDT during summer months.

What are some interesting facts about CST?

CST covers 20 US states fully or partially. Chicago and Houston are the two largest cities in the Central Time Zone.

Which cities are in the IRST timezone?

Major cities in the IRST timezone include Tehran, Isfahan, Mashhad, Tabriz, Shiraz, Karaj.

What is the UTC offset for IRST?

Iran Standard Time (IRST) is at UTC+03:30. During daylight saving time, it shifts to IRDT.

What should I know about the IRST timezone?

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).

When is it midnight in Chicago, what time is it in IRST?

When it is 12:00 AM (midnight) in Chicago (CST), it is +8h 30m later in IRST (IRST).

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