How to Calculate Time Differences Between Cities Quickly
Three methods to find the time in another city: mental math, UTC offsets, and tools.
The quickest way: use a tool
If you need an exact answer right now, skip the math and use a free converter. Our timezone converter handles DST automatically — pick a source and target zone, enter a date and time, and you get the answer. Bookmark it.
For just "what time is it RIGHT NOW in city X," browse our world clock showing live time in 5000+ cities.
That said, knowing the math is useful when you can't reach for a tool — like when you're in a meeting and someone asks "can we move this to 2 PM their time?"
Method 1: Use UTC offsets (most accurate)
Every time zone is expressed as an offset from UTC (Coordinated Universal Time), formerly known as GMT. For example:
- UTC-8: Los Angeles (Pacific Standard Time)
- UTC-5: New York (Eastern Standard Time)
- UTC+0: London (Greenwich Mean Time)
- UTC+1: Paris, Berlin (Central European Time)
- UTC+5:30: Mumbai, Delhi (Indian Standard Time)
- UTC+8: Beijing, Singapore
- UTC+9: Tokyo (Japan Standard Time)
- UTC+10: Sydney (Australian Eastern Standard Time)
The formula: (City A's local time) − (A's UTC offset) + (B's UTC offset) = City B's local time
Example: What's 3 PM in Los Angeles in Mumbai terms?
- LA = UTC-8, Mumbai = UTC+5:30
- Difference = +13:30
- 3 PM LA + 13:30 = 4:30 AM the next day in Mumbai
Method 2: Memorize relative offsets (fastest)
If you regularly work with the same set of cities, just memorize their relative differences from your own time:
- "London is 5 hours ahead of NYC"
- "Mumbai is 12.5 hours ahead of NYC"
- "Tokyo is 13 hours ahead of NYC"
- "Sydney is 14 hours ahead of NYC (16 during their summer DST)"
The math becomes mental: if it's 10 AM NYC, London is 3 PM, Mumbai is 10:30 PM, Tokyo is 11 PM.
Method 3: The fingers trick
An old reporter's trick for live mental math when you can't use a calculator:
- Visualize a clock with your home city at 12.
- For "ahead" cities (east of you), count clockwise. London +5 from NYC means visualize London at the 5 o'clock position.
- If it's 10 AM NYC (top of clock), London is at "10 + 5 = 3 PM."
- For "behind" cities (west of you), count counterclockwise.
Works for back-of-napkin estimates; not for precise DST-handling.
The DST trap (why mental math fails)
UTC offsets are constant by law, but the relative difference between two cities changes during the year because of DST. Examples:
- NYC and London: Normally 5 hours apart. But during a 2-3 week window each spring and fall when only one has switched DST, the difference is 4 hours.
- NYC and India: India never observes DST. So in summer (NYC on EDT), the gap is 9.5 hours. In winter (NYC on EST), the gap is 10.5 hours.
- Sydney and most of the world: Australia's DST runs opposite to the Northern Hemisphere (Oct-Apr). The relative difference shifts twice a year for confusing reasons.
This is why you can't memorize "Mumbai is 9.5 hours ahead of NYC" — sometimes it's 10.5. Use a tool that handles DST for anything important.
Useful cheats for common conversions
These rules of thumb work most of the year:
- NYC ↔ LA: 3 hours west (LA is earlier)
- NYC ↔ Chicago: 1 hour west
- NYC ↔ London: 5 hours east (Nov-Mar) or 4 hours east (Mar-Oct)
- NYC ↔ Paris/Berlin: 6 hours east (Nov-Mar) or 5 hours east (Mar-Oct)
- NYC ↔ Mumbai: 9.5h (Mar-Oct) or 10.5h (Nov-Mar)
- NYC ↔ Tokyo: 13h (Mar-Oct) or 14h (Nov-Mar)
- NYC ↔ Sydney: 14h, 15h, or 16h depending on whose DST is active
- London ↔ Mumbai: 4.5 hours east, year-round (Mumbai doesn't observe DST)
- London ↔ Tokyo: 9 hours east in their winter, 8 hours in their summer
For meeting planning
When scheduling a meeting across zones, think in terms of "reasonable hours" for each city:
- Reasonable working hours: 8 AM to 6 PM local time for the attendee.
- Stretchable hours: 7 AM to 8 PM local — fine occasionally, not as a regular slot.
- Hostile hours: Before 7 AM or after 8 PM. Avoid except for emergencies.
For three or more zones, you'll often find there is no single hour in all participants' "reasonable" ranges. Either rotate who gets the bad slot, or move to async. See our guide to multi-timezone work.
Bookmarkable city pages
If you regularly check "what time is it in X," bookmark the dedicated page for that city — it's faster than typing the city name into a search every time: