Basetime

Jet lag calculator — light & sleep plan by route

Jet lag comes from the number of time zones you cross and the direction you fly. East is harder than west, and light at the right time is the fastest fix. Pick your route below for a day-by-day sleep and daylight plan in the destination's local time.

Toronto → Hong Kong
12 zones east · ~12 days · severe
New York → Tokyo
11 zones west · ~8 days · severe
London → Sydney
9 zones east · ~9 days · severe
London → Tokyo
8 zones east · ~8 days · severe
Tokyo → London
8 zones west · ~6 days · severe
San Francisco → London
8 zones east · ~8 days · severe
London → Los Angeles
8 zones west · ~6 days · severe
San Francisco → Tokyo
8 zones west · ~6 days · severe
Los Angeles → Sydney
7 zones west · ~5 days · severe
Sydney → Los Angeles
7 zones east · ~7 days · severe
London → Singapore
7 zones east · ~7 days · severe
Singapore → London
7 zones west · ~5 days · severe
New York → Paris
6 zones east · ~6 days · severe
Dubai → Sydney
6 zones east · ~6 days · severe
Chicago → London
6 zones east · ~6 days · severe
New York → London
5 zones east · ~5 days · moderate
London → New York
5 zones west · ~4 days · moderate
New York → Los Angeles
3 zones west · ~2 days · moderate
Los Angeles → New York
3 zones east · ~3 days · moderate
London → Dubai
3 zones east · ~3 days · moderate

How the calculator works

Jet lag is a mismatch between your body clock and the local day. Cross five time zones and your internal clock is five hours off; because it can only shift by roughly an hour a day, it takes several days to catch up. Basetime works out the exact shift for your route from live time-zone data — daylight saving included — then decides whether you need to advance your clock (fly east, go to bed earlier) or delay it (fly west, stay up later).

The direction matters more than most people think. Our natural rhythm runs a little longer than 24 hours, so stretching the day westward is comfortable, while compressing it eastward is a fight. That's why the same five-zone hop feels rougher going New York → London than the other way around, and why the recovery estimate on each route page is longer for eastward trips.

Light is the lever that actually moves the clock. Get bright daylight at the right time and you can shift an hour or more per day; get it at the wrong time and you push yourself backwards. Each route page places the light-seeking and light-avoiding windows on the correct side of your day and lays out a night-by-night sleep target in the destination's local time — so you can start adjusting on the plane and arrive most of the way there.

Pick a route above to get your plan. Flying a pairing we haven't listed yet? The engine covers every zone, so more routes are on the way — or check the local time and sun times for your destination in the meantime.

FAQ

What causes jet lag?

Your body clock is still set to where you left. Every time zone you cross is an hour it has to shift, and it can only move about an hour a day — so a long-haul flight leaves your internal clock out of sync with the local day.

Why is flying east worse than west?

Flying east forces a phase advance — an earlier bedtime — which fights the body's natural tendency to run slightly longer than 24 hours. Flying west is a phase delay (later bedtime), which is easier, so westward trips settle a day or two faster.

What's the fastest way to beat jet lag?

Well-timed bright light. After an eastward trip, chase morning light and dim the evenings; after a westward trip, get evening light and shade your early mornings. Each route page gives you the exact windows in local time.