Atlantic Daylight Time is 3 hours ahead of Mountain Daylight Time.

Frequently asked

Quick answers about converting between Atlantic Daylight Time and Mountain Daylight Time. Can't find what you need? Email [email protected].

What is the time difference between Atlantic Daylight Time and Mountain Daylight Time?

Atlantic Daylight Time is 3 hours ahead of Mountain Daylight Time right now. We always show the live, daylight-saving-correct difference, so this figure already accounts for whichever side is observing summer time today.

When it's 9am in Atlantic Daylight Time, what time is it in Mountain Daylight Time?

9am in Atlantic Daylight Time is 6am in Mountain Daylight Time. Use the hour-by-hour table above to read any other time across — find the row and read the matching cell in the other column.

What's the best time for a call between Atlantic Daylight Time and Mountain Daylight Time?

12pm–5pm in Atlantic Daylight Time lines up with 9am–2pm in Mountain Daylight Time — both sides are inside a 9-to-5 working day.

Does this account for daylight saving time?

Yes. We track every clock change in both places, so the abbreviations you see — ADT and MDT — are the ones actually in effect right now, not a fixed all-year value. When either side changes its clocks, this page updates automatically.

Why is the date sometimes different on each side?

When two places are far enough apart, the same moment can fall on different calendar days. That is why some conversions are marked "previous day" or "next day" — it is the same instant in time, read off two clocks that crossed midnight at different points.