KST to AST
-13hKST
KSTSOURCEAST
ASTGreen rows indicate typical business hours (9 AM - 5 PM)
KST and AST on the World Map
The map below highlights the KST (Korea Standard Time) and AST (Atlantic Standard Time) timezone regions across the globe.
KST – Korea Standard Time
UTC+09:00Korea Standard Time (KST) is the time zone for South Korea, 9 hours ahead of UTC.
- •South Korea does not observe daylight saving time.
- •Seoul is home to Samsung, LG, and Hyundai headquarters.
- •KST is the same offset as JST (UTC+09:00).
AST – Atlantic Standard Time
UTC-04:00Atlantic Standard Time (AST) is the time zone for the Canadian Atlantic provinces and the Caribbean, 4 hours behind UTC.
- •Puerto Rico uses AST year-round and does not observe DST.
- •AST is 1 hour ahead of EST.
- •Halifax, the capital of Nova Scotia, is the largest city in AST Canada.
Time Conversion Guide: KST to AST
KST runs on Korea Standard Time (KST) at UTC+09:00. AST runs on Atlantic Standard Time (AST) at UTC-04:00. That puts KST 13 hours behind AST — a difference of -13h at the current offsets.
In practice, when it is 9:00 AM in KST it is 8:00 PM in AST on the previous day. Midnight in KST is 11:00 AM in AST. Neither zone observes daylight saving time, so the offset between them stays constant all year.
KST to AST time conversion table
| KST (KST) | AST (AST) | Day |
|---|---|---|
| 12:00 AM | 11:00 AM | previous day |
| 6:00 AM | 5:00 PM | previous day |
| 7:00 AM | 6:00 PM | previous day |
| 8:00 AM | 7:00 PM | previous day |
| 9:00 AM | 8:00 PM | previous day |
| 12:00 PM | 11:00 PM | previous day |
| 3:00 PM | 2:00 AM | same day |
| 5:00 PM | 4:00 AM | same day |
| 6:00 PM | 5:00 AM | same day |
| 9:00 PM | 8:00 AM | same day |
Why people convert KST to AST time
- Scheduling a call from KST to AST: a 10:00 AM start in KST lands at 9:00 PM in AST the previous day, so you can confirm the slot without doing the arithmetic yourself.
- Handling a -13h gap: KST and AST 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 AST is 8:00 PM in KST.
- Keeping family and friends in sync: knowing that 8:00 PM in KST is 7:00 AM in AST makes it easy to avoid calling at 3 AM.
- Always state the zone abbreviation, not just the hour. "3:00 PM KST" is unambiguous; "3 PM" across a -13h gap is not.
- With a -13h gap there is no shared 9-to-5 window, so alternate the early start: one week KST takes the early slot, the next week AST does.
About KST (Korea Standard Time)
Korea Standard Time (KST) is the time zone used in South Korea. It shares the same UTC offset as Japan Standard Time but is a distinct time zone. South Korea does not observe daylight saving time. Seoul, the capital, is a major global tech and business hub.
About AST (Atlantic Standard Time)
Atlantic Standard Time (AST) covers Canada's Atlantic provinces (Nova Scotia, New Brunswick, Prince Edward Island, and most of Labrador), as well as several Caribbean nations. Puerto Rico and the US Virgin Islands use AST year-round without daylight saving time. The Canadian provinces switch to Atlantic Daylight Time (ADT) in summer.
Best time to call between KST and AST
With a -13h offset there is no overlap inside a normal 9 AM – 5 PM day. AST opens at 9:00 AM AST, which is 8:00 PM in KST, so real-time calls need an early-morning or late-evening slot on one side.
Business hours overlap
KST and AST have no shared working hours because of the -13h gap. Teams need to alternate early starts or rely on asynchronous handovers.
KST is 13 hours behind AST (KST UTC+09:00 → AST UTC-04:00). 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
KST
Does not observe DST
AST
☀ Currently in DST
Standard: UTC-04:00 · DST: UTC-03:00
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 KST and AST?
KST (KST, UTC+09:00) is 13 hours behind AST (AST, UTC-04:00). The gap is currently -13h.
How do I convert KST time to AST time?
Add -13h to KST local time. For example, 9:00 AM in KST is 8:00 PM in AST (previous day).
What time is it in AST right now?
AST uses AST at UTC-04:00. Use the live converter at the top of this page — it updates in real time and already accounts for the -13h offset from KST.
What is the best time to call AST from KST?
There is no shared working-hours window because of the -13h gap. The closest option is 1:00 PM in KST, which is 12:00 AM in AST.
Which is behind, KST or AST?
KST is 13 hours behind AST. When it is 12:00 PM in KST it is 11:00 PM in AST.
Does daylight saving time affect the KST–AST difference?
Neither zone observes daylight saving time, so the -13h offset between KST and AST is fixed all year.
Which other cities share KST's time zone?
KST also covers Seoul, Busan, Incheon, Daegu, Daejeon, Pyongyang.
Which countries use KST, KST's zone?
KST is used in South Korea, North Korea.
Is there a day difference between KST and AST?
Sometimes. The -13h gap is large enough that 8:00 PM or later in KST already falls on the in AST.
What is the time difference between KST and AST?
AST is -13h from KST.
What timezone is KST in?
KST operates on its local timezone.
What timezone is AST in?
AST operates on its local timezone.
Which countries use KST (Korea Standard Time)?
KST is used in South Korea, North Korea.
Does KST observe daylight saving time?
No, KST does not observe daylight saving time and remains at UTC+09:00 year-round.
What are some interesting facts about KST?
South Korea does not observe daylight saving time. Seoul is home to Samsung, LG, and Hyundai headquarters.
Which cities are in the AST timezone?
Major cities in the AST timezone include Halifax, San Juan, Santo Domingo, Caracas, La Paz, Fredericton, Charlottetown.
What is the UTC offset for AST?
Atlantic Standard Time (AST) is at UTC-04:00. During daylight saving time, it shifts to ADT.
What should I know about the AST timezone?
Puerto Rico uses AST year-round and does not observe DST. AST is 1 hour ahead of EST.
When is it midnight in KST, what time is it in AST?
When it is 12:00 AM (midnight) in KST (KST), it is -13h later in AST (AST).
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