IRST to CST
-9h 30mIRST
IRSTSOURCECST
CSTGreen rows indicate typical business hours (9 AM - 5 PM)
IRST and CST on the World Map
The map below highlights the IRST (Iran Standard Time) and CST (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.
Time Conversion Guide: IRST to CST
IRST runs on Iran Standard Time (IRST) at UTC+03:30. CST runs on Central Standard Time (CST) at UTC-06:00. That puts IRST 9 hours 30 minutes behind CST — a difference of -9h 30m at the current offsets.
In practice, when it is 9:00 AM in IRST it is 11:30 PM in CST on the previous day. Midnight in IRST is 2:30 PM in CST. Neither zone observes daylight saving time, so the offset between them stays constant all year.
IRST to CST time conversion table
| IRST (IRST) | CST (CST) | Day |
|---|---|---|
| 12:00 AM | 2:30 PM | previous day |
| 6:00 AM | 8:30 PM | previous day |
| 7:00 AM | 9:30 PM | previous day |
| 8:00 AM | 10:30 PM | previous day |
| 9:00 AM | 11:30 PM | previous day |
| 12:00 PM | 2:30 AM | same day |
| 3:00 PM | 5:30 AM | same day |
| 5:00 PM | 7:30 AM | same day |
| 6:00 PM | 8:30 AM | same day |
| 9:00 PM | 11:30 AM | same day |
Why people convert IRST to CST time
- Scheduling a call from IRST to CST: a 10:00 AM start in IRST lands at 12:30 AM in CST, so you can confirm the slot without doing the arithmetic yourself.
- Handling a -9h 30m gap: IRST and CST 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 CST is 11:30 PM in IRST.
- Coordinating a IRST-based team with CST 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 -9h 30m gap is not.
- With a -9h 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 CST does.
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 CST
With a -9h 30m offset there is no overlap inside a normal 9 AM – 5 PM day. CST opens at 9:00 AM CST, which is 11:30 PM in IRST, so real-time calls need an early-morning or late-evening slot on one side.
Business hours overlap
IRST and CST have no shared working hours because of the -9h 30m gap. Teams need to alternate early starts or rely on asynchronous handovers.
IRST is 9 hours 30 minutes behind CST (IRST UTC+03:30 → CST UTC-06:00). 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
CST
☀ 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 CST?
IRST (IRST, UTC+03:30) is 9 hours 30 minutes behind CST (CST, UTC-06:00). The gap is currently -9h 30m.
How do I convert IRST time to CST time?
Add -9h 30m to IRST local time. For example, 9:00 AM in IRST is 11:30 PM in CST (previous day).
What time is it in CST right now?
CST uses CST at UTC-06:00. Use the live converter at the top of this page — it updates in real time and already accounts for the -9h 30m offset from IRST.
What is the best time to call CST from IRST?
There is no shared working-hours window because of the -9h 30m gap. The closest option is 1:00 PM in IRST, which is 3:30 AM in CST.
Which is behind, IRST or CST?
IRST is 9 hours 30 minutes behind CST. When it is 12:00 PM in IRST it is 2:30 AM in CST.
Does daylight saving time affect the IRST–CST difference?
Neither zone observes daylight saving time, so the -9h 30m offset between IRST and CST is fixed all year.
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 CST?
Not normally. The -9h 30m gap only pushes the date over the previous day.
What is the time difference between IRST and CST?
CST is -9h 30m from IRST.
What timezone is IRST in?
IRST operates on its local timezone.
What timezone is CST in?
CST operates on its local timezone.
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 CST?
When it is 12:00 AM (midnight) in IRST (IRST), it is -9h 30m later in CST (CST).
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See every conversion from IRST →·See every conversion from CST →