CST to IRST
+9h 30mCST
CSTSOURCEIRST
IRSTGreen rows indicate typical business hours (9 AM - 5 PM)
CST and IRST on the World Map
The map below highlights the CST (Central Standard Time) and IRST (Iran Standard Time) timezone regions across the globe.
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.
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.
Understanding the +9h 30m Gap: CST vs IRST
CST runs on Central Standard Time (CST) at UTC-06:00. IRST runs on Iran Standard Time (IRST) at UTC+03:30. That puts CST 9 hours 30 minutes ahead of IRST — a difference of +9h 30m at the current offsets.
In practice, when it is 9:00 AM in CST it is 6:30 PM in IRST. Midnight in CST is 9:30 AM in IRST. Neither zone observes daylight saving time, so the offset between them stays constant all year.
CST to IRST time conversion table
| CST (CST) | IRST (IRST) | Day |
|---|---|---|
| 12:00 AM | 9:30 AM | same day |
| 6:00 AM | 3:30 PM | same day |
| 7:00 AM | 4:30 PM | same day |
| 8:00 AM | 5:30 PM | same day |
| 9:00 AM | 6:30 PM | same day |
| 12:00 PM | 9:30 PM | same day |
| 3:00 PM | 12:30 AM | next day |
| 5:00 PM | 2:30 AM | next day |
| 6:00 PM | 3:30 AM | next day |
| 9:00 PM | 6:30 AM | next day |
Why people convert CST to IRST time
- Scheduling a call from CST to IRST: a 10:00 AM start in CST lands at 7:30 PM in IRST, so you can confirm the slot without doing the arithmetic yourself.
- Handling a +9h 30m gap: CST 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 6:30 PM in CST.
- Keeping family and friends in sync: knowing that 8:00 PM in CST is 5:30 AM in IRST makes it easy to avoid calling at 3 AM.
- Always state the zone abbreviation, not just the hour. "3:00 PM CST" 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 CST takes the early slot, the next week IRST does.
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 CST and IRST
With a +9h 30m offset there is no overlap inside a normal 9 AM – 5 PM day. IRST opens at 9:00 AM IRST, which is 6:30 PM in CST, so real-time calls need an early-morning or late-evening slot on one side.
Business hours overlap
CST and IRST have no shared working hours because of the +9h 30m gap. Teams need to alternate early starts or rely on asynchronous handovers.
CST is 9 hours 30 minutes ahead of IRST (CST UTC-06:00 → 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
CST
☀ 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:
Frequently Asked Questions
What is the time difference between CST and IRST?
CST (CST, UTC-06:00) is 9 hours 30 minutes ahead of IRST (IRST, UTC+03:30). The gap is currently +9h 30m.
How do I convert CST time to IRST time?
Add +9h 30m to CST local time. For example, 9:00 AM in CST is 6:30 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 +9h 30m offset from CST.
What is the best time to call IRST from CST?
There is no shared working-hours window because of the +9h 30m gap. The closest option is 1:00 PM in CST, which is 10:30 PM in IRST.
Which is ahead, CST or IRST?
CST is 9 hours 30 minutes ahead of IRST. When it is 12:00 PM in CST it is 9:30 PM in IRST.
Does daylight saving time affect the CST–IRST difference?
Neither zone observes daylight saving time, so the +9h 30m offset between CST and IRST is fixed all year.
Which other cities share CST's time zone?
CST also covers Chicago, Houston, Dallas, San Antonio, Mexico City, Austin, Winnipeg, Memphis and 6 more.
Which countries use CST, CST's zone?
CST 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 CST and IRST?
Not normally. The +9h 30m gap only pushes the date over for late-evening times.
What is the time difference between CST and IRST?
IRST is +9h 30m from CST.
What timezone is CST in?
CST operates on its local timezone.
What timezone is IRST in?
IRST operates on its local timezone.
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 CST, what time is it in IRST?
When it is 12:00 AM (midnight) in CST (CST), it is +9h 30m later in IRST (IRST).
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See every conversion from CST →·See every conversion from IRST →