# Jet Lag Planner

> A day-by-day sleep, light and caffeine plan to beat jet lag, with calendar export. Pick your home and destination time zones, travel date and usual sleep times. The planner computes the real time difference for that date (including daylight saving), shifts your sleep before departure, and lists when to seek or avoid bright light and when to stop caffeine until you are adapted. Download it as a calendar file.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://jetlagplanner.usefulweb.site/ (interactive tool at https://jetlagplanner.usefulweb.site/tool)
- JSON API: POST https://jetlagplanner.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://jetlagplanner.usefulweb.site/api/v1/tool)
- OpenAPI: https://jetlagplanner.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://jetlagplanner.usefulweb.site/mcp - tool `jet_lag_planner`

## Inputs
- homeZone (select): Home time zone
- destinationZone (select): Destination time zone
- homeZoneCustom (text): Other home zone (IANA name) - Overrides the list if filled in.
- destinationZoneCustom (text): Other destination zone (IANA name) - Overrides the list if filled in.
- departureDate (date, required): Departure date
- arrivalDate (date): Arrival date (local) - Defaults to the departure date.
- bedtime (time): Usual bedtime
- wakeTime (time): Usual wake time
- daysBefore (integer): Days to pre-adjust before departure
- chronotype (select): Chronotype

## Method
- Time difference = destination UTC offset (at noon UTC on the arrival date) − home UTC offset (at noon UTC on the departure date), via the Intl time-zone database, so daylight saving is included. It is normalised to −12…+12 h; positive = eastward (clock must advance), negative = westward (delay).
- Pre-flight: sleep and wake move 1 hour per day toward destination time (earlier for east, later for west), as suggested in the CDC Yellow Book jet-lag chapter for the 2–3 days before travel; days beyond what is needed are skipped.
- After arrival you sleep on local time; the body clock is assumed to catch up 1 h/day after eastward and 1.5 h/day after westward travel (common planning rule of thumb, not an individual prediction).
- Core body temperature minimum (CBTmin) is estimated at 2.5 h before the body’s habitual wake time (2 h for early birds, 3 h for night owls).
- Light rule (phase-response curve): to advance (east) seek bright light in the 3 h after CBTmin and avoid it in the 3 h before; to delay (west) seek light in the 3 h before CBTmin and avoid it in the 3 h after. If a window falls while you sleep, use only its waking part.
- Caffeine cut-off = 6 h before planned bedtime (CDC Yellow Book example).
- The .ics file contains bedtime, light and caffeine events in UTC with UIDs derived from a hash of your inputs, CRLF line endings and folded lines.

## Limits
- General planning guidance, not medical advice. Ask a clinician before using melatonin or sleep medication.