Five hours. That is the number most people keep in their heads when they think about the time difference between UK and America. You're in London, you want to call your friend in New York, and you just subtract five. It’s a simple rule of thumb. Except, honestly, it’s often wrong. If you’ve ever sat waiting for a Zoom call that nobody else joined, or you woke up your sister in California at 4:00 AM because you forgot about the Pacific Ocean, you know the math isn't always that clean.
The United States is massive. It's roughly 40 times the size of the UK. While the United Kingdom sits snugly within a single time zone—Greenwich Mean Time (GMT) in the winter and British Summer Time (BST) in the summer—America is sliced into six different primary time zones. Then you have the Daylight Saving Time (DST) trap. Every year, there are these weird two-to-three-week windows where the gap shrinks or grows because the UK and the US don't change their clocks on the same day. It's a logistical nightmare for businesses and families alike.
The coastal divide and why New York isn't the whole story
Most people default to Eastern Time because that’s where the stock markets and the big news networks live. When it’s noon in London, it’s 7:00 AM in New York. That’s your five-hour gap. But America keeps going west. It keeps going for thousands of miles.
If you're looking at Chicago or Dallas, you're in Central Time. Now the gap is six hours. Head further west to Denver or Salt Lake City in the Mountain Time Zone, and you're looking at seven hours. By the time you reach the West Coast—Los Angeles, San Francisco, Seattle—the time difference between UK and America has stretched to a massive eight hours. If you’re in London and finishing your dinner at 8:00 PM, your friend in LA is just starting their lunch at noon. It makes real-time gaming or collaborative work almost impossible without someone losing sleep.
Then there is the Alaska Time Zone (nine hours behind the UK) and Hawaii-Aleutian Time (ten or eleven hours behind). Hawaii is actually a great example of the complexity here because they don't participate in Daylight Saving Time at all. While the rest of the US is jumping forward and backward, Hawaii stays put.
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The two-week glitch that ruins your calendar
This is where things get genuinely annoying. The United States usually enters Daylight Saving Time on the second Sunday in March and exits on the first Sunday in November. The UK, following the European schedule, typically changes its clocks on the last Sunday in March and the last Sunday in October.
This creates a "glitch" period.
In late March, for about two weeks, the time difference between UK and America actually narrows by one hour. New York is suddenly only four hours behind London instead of five. Then, in the autumn, the UK drops back to GMT before the US drops back to Standard Time, widening the gap for a week.
If you work for a global company, this is the week where everything breaks. I’ve seen senior VPs miss board meetings because their Outlook calendar synced to one region’s change but not the other. You can't just trust your phone to do the heavy lifting during these transition windows. You have to manually verify.
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A quick look at the zones (Standard Time)
- London to New York (Eastern): 5 Hours.
- London to Chicago (Central): 6 Hours.
- London to Denver (Mountain): 7 Hours.
- London to Los Angeles (Pacific): 8 Hours.
- London to Anchorage (Alaska): 9 Hours.
- London to Honolulu (Hawaii): 11 Hours.
The Arizona and Hawaii exception
Arizona is a bit of a rebel. Most of the state does not observe Daylight Saving Time. They decided a long time ago that they have enough sunlight and don't need to "save" any more of it. However, the Navajo Nation, which covers a large portion of northeastern Arizona, does observe DST.
Imagine driving across the state of Arizona in the summer. You could technically change your watch three or four times in a single afternoon just by crossing tribal land borders. For someone in the UK trying to coordinate a shipment or a call to a warehouse in Phoenix, you have to remember that in the summer, Arizona is effectively on the same time as California (Pacific), but in the winter, they align with the Mountain time zone. It is enough to give anyone a headache.
Practical ways to manage the gap without losing your mind
If you are dealing with the time difference between UK and America daily, you need a system. Relying on "I think they are five hours behind" is a recipe for disaster, especially when the West Coast is involved.
- Use a World Clock that shows "Duration of Overlap": Instead of just looking at what time it is there, look at your "Golden Hours." These are the hours where both regions are awake and working. For London and New York, this is usually 1:00 PM to 5:00 PM GMT. For London and LA, the window is tiny—usually just 4:00 PM to 6:00 PM GMT.
- The "Tomorrow" Problem: When you send an email late at night in the UK, it’s still the afternoon in the US. They might reply, and you’ll see it when you wake up. But if you're on the US West Coast and send an email at 5:00 PM Friday, your UK contact won't see it until Monday morning. You've essentially lost a whole weekend of progress.
- Check the "Spring Forward" Dates Yearly: Seriously. Put a reminder in your phone for the second Sunday in March and the last Sunday in March. Label it "Time Zone Chaos."
- Military Time is your friend: When communicating across these zones, using a 24-hour clock (like 17:00 instead of 5:00) prevents the "Wait, did you mean 5:00 AM or 5:00 PM?" confusion.
Jet lag is a physiological reality
Traveling across these zones is a different beast. Going from the UK to the US (Westward) is generally considered "easier." You are essentially gaining hours. You might feel tired by 8:00 PM New York time because your body thinks it’s 1:00 AM, but you can usually power through.
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Coming back? That’s the killer. Going Eastward from the US to the UK means you are "losing" time. You leave New York at 9:00 PM, fly for seven hours, and land in London at 9:00 AM. Your body thinks it’s 4:00 AM. You’ve missed an entire night of sleep. Experts from the Sleep Foundation often suggest shifting your bedtime by one hour each night for three days before you fly to help mitigate the shock to your circadian rhythm.
What to do next
To handle the time difference between UK and America effectively, stop calculating it manually in your head during the transition months of March and October.
- Download a dedicated time zone app like World Time Buddy or use the "Clocks" feature on your smartphone to save specific cities like "Phoenix," "New York," and "London" side-by-side.
- Verify the specific dates for the next clock change in both countries; in 2026, the US shifts on March 8, while the UK waits until March 29.
- Always include the time zone abbreviation (GMT, BST, ET, PT) in meeting invites to ensure there is a single source of truth for all participants.
By acknowledging the complexity of the US landscape—and the quirks of the DST calendar—you can avoid the most common scheduling blunders that plague international relations.