Jet Lag Calculator
Estimate how many days it takes to recover from jet lag based on the time zones you cross and your direction of travel, with the recovery rule of thumb explained.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Estimate how many days it takes to recover from jet lag based on time zones crossed and travel direction.
Show the formula & steps
How the Jet Lag Calculator Works
Jet lag happens when your internal body clock is still set to your departure time zone while you have arrived in another. This calculator estimates the recovery time based on the two factors that matter most: how many time zones you cross and your direction of travel.
Enter the number of time zones between origin and destination, then choose eastbound or westbound. The tool returns an estimated number of recovery days and a rough severity rating.
The Formula
Sleep researchers commonly summarize jet lag recovery with a simple rate:
Recovery (days) ≈ time zones crossed × rate Eastbound rate ≈ 1 day per time zone Westbound rate ≈ 1 day per 1.5 time zones (about 0.67 days per zone)
Crossing two or fewer time zones is treated as negligible, since small shifts sit within normal daily variation. The result is rounded up to whole days for planning.
Worked Example
You fly eastbound across 8 time zones (for example, US East Coast to much of Europe is closer to 5–6; a longer haul like the US to East Asia can be 8 or more):
- Direction: eastbound, rate = 1 day per zone
- Recovery ≈ 8 × 1.0 = 8 days
The same 8-zone trip westbound would estimate:
- Recovery ≈ 8 × 0.67 = 5.33 → rounded up to 6 days
This is why returning west often feels easier than flying east.
Estimated Recovery by Zones Crossed
These are planning estimates, rounded up to whole days:
| Time zones | Eastbound | Westbound |
|---|---|---|
| 3 | 3 days | 2 days |
| 5 | 5 days | 4 days |
| 8 | 8 days | 6 days |
| 11 | 11 days | 8 days |
Beating Jet Lag
- Pre-adjust your clock. Shift sleep and meals an hour or so toward the destination for a few days before departure.
- Use light strategically. Morning light helps after eastward flights; evening light helps after westward flights.
- Adopt local time immediately. Eat and sleep on the new schedule the moment you land.
- Stay hydrated and limit alcohol. Both speed how quickly you feel normal again.
Treat the number above as a guide for scheduling meetings or rest days, not as a medical figure.
Frequently asked questions
How long does jet lag last?+
A common rule of thumb is that the body clock re-synchronizes about one time zone per day. Traveling east is usually harder, so plan on roughly one recovery day per time zone, while traveling west often resolves faster, closer to one day for every one and a half zones crossed.
Why is jet lag worse traveling east?+
The human body clock runs slightly longer than 24 hours, so it is easier to delay (stay up later, which happens when flying west) than to advance (go to sleep earlier, which flying east demands). Advancing the clock is harder for most people, so eastbound jet lag tends to be more severe and longer-lasting.
Do you get jet lag from crossing one or two time zones?+
Usually very little. Shifts of one to two hours fall within the body's normal day-to-day variation, so most travelers feel only minor effects. Noticeable jet lag typically starts at around three or more time zones, which is why this calculator treats two or fewer zones as negligible.
How can I recover from jet lag faster?+
Shift your sleep schedule a little toward the destination before you leave, get bright light at the right times (morning light helps after eastward travel, evening light after westward), stay hydrated, and adopt local meal and sleep times on arrival. These habits help your clock adjust quicker than the average rate.
Is this jet lag estimate exact?+
No. It is a general planning guide based on a widely cited recovery rate, not a medical prediction. Actual recovery depends on age, individual sleep patterns, light exposure, flight timing, and how well you manage sleep before and after travel. Use it to set expectations, not as medical advice.