CST to AST Time Converter
AST is 2 hours ahead of CST. The US Central states are currently on CDT (UTC-5:00), and Atlantic Canada and the Caribbean are currently on ADT (UTC-3:00).
Best Time to Call Between CST and AST
Both zones are inside normal business hours between 9:00 AM and 3:00 PM CST — that's 11:00 AM to 5:00 PM AST. That's a 6-hour window.
both at work CST only AST only neither — hours along the strip are CST.
Common Times Converted
CST on the left, AST on the right.
CST to AST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| CST | AST | Working hours |
|---|---|---|
| 12:00 AM | 2:00 AM | — |
| 1:00 AM | 3:00 AM | — |
| 2:00 AM | 4:00 AM | — |
| 3:00 AM | 5:00 AM | — |
| 4:00 AM | 6:00 AM | — |
| 5:00 AM | 7:00 AM | — |
| 6:00 AM | 8:00 AM | — |
| 7:00 AM | 9:00 AM | AST only |
| 8:00 AM | 10:00 AM | AST only |
| 9:00 AM | 11:00 AM | Both zones |
| 10:00 AM | 12:00 PM | Both zones |
| 11:00 AM | 1:00 PM | Both zones |
| 12:00 PM | 2:00 PM | Both zones |
| 1:00 PM | 3:00 PM | Both zones |
| 2:00 PM | 4:00 PM | Both zones |
| 3:00 PM | 5:00 PM | CST only |
| 4:00 PM | 6:00 PM | CST only |
| 5:00 PM | 7:00 PM | — |
| 6:00 PM | 8:00 PM | — |
| 7:00 PM | 9:00 PM | — |
| 8:00 PM | 10:00 PM | — |
| 9:00 PM | 11:00 PM | — |
| 10:00 PM | 12:00 AM next day | — |
| 11:00 PM | 1:00 AM next day | — |
What CST and AST Actually Are
CST — Central Standard Time
Chicago, Houston, Dallas, Mexico City, Winnipeg. Standing at UTC-6:00 as written, and the region does change its clocks, so its live offset moves by an hour twice a year. The next change is on Sunday, November 1, 2026, to CST. CST also stands for China Standard Time (UTC+8) and Cuba Standard Time (UTC-5). This page covers the North American one.
Saskatchewan sits inside the Central zone but never changes its clocks, so it matches CST in winter and its neighbors' MDT in summer.
AST — Atlantic Standard Time
Halifax, San Juan, Santo Domingo, Bermuda. Standing at UTC-4:00 as written, and the region does change its clocks, so its live offset moves by an hour twice a year. The next change is on Sunday, November 1, 2026, to AST. AST also stands for Arabia Standard Time (UTC+3), used in Saudi Arabia, Iraq and Kuwait.
Atlantic Standard Time is the only North American zone whose name is more commonly associated, worldwide, with a completely different zone — Arabia Standard Time.
What This Means in Practice
Both sides change clocks, on different dates
Both regions observe daylight saving but do not switch on the same day, so for a week or two each spring and fall the gap between them is an hour different from the rest of the year. Those short windows are where recurring invitations quietly break.
Close enough to share a working day
At only 2 hours apart, the two working days overlap almost completely. Scheduling is barely constrained by the difference.
Major Cities in Each Zone
Cities on CST
Cities on AST
Frequently Asked Questions
What is the time difference between CST and AST?
AST is 2 hours ahead of CST.
What is 9:00 AM CST in AST?
9:00 AM CST is 11:00 AM AST.
What are the best hours to schedule a call between CST and AST?
Between 9:00 AM and 3:00 PM CST, which is 11:00 AM to 5:00 PM AST. Both sides are inside normal business hours through that window.
Does the difference between CST and AST change during the year?
Yes. Both regions observe daylight saving, and they do not switch on the same dates, so the gap shifts by an hour at least twice a year. The next clock change is on Sunday, November 1, 2026.
Does CST always mean Central Standard Time?
CST also stands for China Standard Time (UTC+8) and Cuba Standard Time (UTC-5). This page covers the North American one.
Does AST always mean Atlantic Standard Time?
AST also stands for Arabia Standard Time (UTC+3), used in Saudi Arabia, Iraq and Kuwait.