Time zone and jet lag calculator: when you land and when you are back to normal
Two questions, one tool. First: what time is it at your destination when you land, and does that still fall on the same calendar day. Second: how long your body needs before it accepts the new time as its own. The second question is usually underestimated. Almost everyone counts on two days, because that is a comfortable number. Going east it is closer to one day per hour the clock jumps forward, and that is the difference between a planned week and a slept-through one.
The flight
The time zones sit inside the tool, as of September 2026. Daylight saving is calculated with the current rules for the EU and North America, and in a simplified way for Australia and New Zealand. Countries that change their rule at short notice are not covered. For the schedule, the airline's own information applies, not this calculation.
Arrival and adjustment
What to do on which day
Everything runs in your browser: the tool loads nothing and stores nothing.
How the arrival time is calculated
The tool takes your departure time as local time, subtracts the offset of the origin and gets the departure in UTC. It adds the air time, then converts the result back into local time with the offset of the destination. One detail hides in there that often goes wrong: the destination offset is taken on the arrival day, not the departure day. Anyone flying on the night of a clock change would otherwise be calculated with two different rules and land an hour off. Daylight saving is not looked up in a table but derived from the rule. For the EU that is the last Sunday in March to the last Sunday in October, for North America the second Sunday in March to the first Sunday in November. Australia and New Zealand sit in the southern hemisphere and run the other way round; we treat them in a simplified way. If the landing falls on a different calendar day, that appears as a marker after the time. On flights to Asia this is the normal case, and it is the most common reason a hotel booking ends up one day off.
Why east is harder than west
Without external cues the body clock runs slightly longer than twenty-four hours. That is why the body finds it easy to stretch a day and hard to shorten one. Flying west means staying up longer. Almost everyone manages that. Flying east means sleeping earlier than the body wants to, and hardly anyone can do that on command. As a rule of thumb we count about one hour of adjustment per day going east and about one and a half going west. Six hours west are done in four days; six hours east need six. The strongest lever is light, not sleep. Going east, bright light in the morning and darkness late in the evening help; going west it is exactly the other way round. The second strongest lever is fixed meal times on local time. Both are in the plan on the right, broken down by day. On short trips the advice inverts. If you fly to New York for two days, do not adjust at all: stay on home time and place appointments so that they fall inside your usual daytime window. The tool spots this case from the length of stay and says so.
What the tool cannot do
It is not a time zone database. The offsets sit inside the tool, as of September 2026, and cover 46 places. Countries that change their daylight saving rule at short notice are not represented, and that happens regularly. It knows no schedules. You enter the flight time yourself, and that means the time in the air. A connection is not flight time; if you want to include it, add the layover. It is not medical advice. The rules of thumb come from sleep research and apply to healthy adults without medication. Anyone taking sleeping pills, melatonin or medication on a fixed schedule should discuss the change with a doctor rather than with a calculator. And it knows nothing about you. Some people are back to normal on day three after an eight-hour shift, others need twice as long. The number is an expectation, not a promise.