Input flights + sleep chronotype + activity goals; AI returns hour-by-hour pre-flight, in-flight, post-arrival behavioral plan (light exposure, caffeine timing, melatonin window, meal schedule). Adjusts in real-time if you miss a step. No subscription lock — $4.99 per trip OR $19/yr unlimited.

What we ship

**Core features (MVP)**

• 3-question chronotype quiz (morning lark / night owl / neutral + sleep window) and a flight input form (outbound + return, autocomplete city + datetime).
• Hour-by-hour behavioral plan: bright-light exposure windows, caffeine cutoff, melatonin window (if user opts in), bedtime shifts per day, meal timing.
• On-trip activity overlay: user marks "important meeting 9am day 1" / "leisure / no meetings" — AI tunes plan to goals, not just arrival.
• Real-time re-adjust: if user marks "missed melatonin", Claude generates an updated plan for remaining hours.
• Full "not medical advice" disclaimer in onboarding + footer of every screen.

**Primary user flow**

1. User finds us via ProductHunt / SEO "jet lag calculator".

2. No signup: enter outbound flight + arrival flight + chronotype quiz + trip goal → see first 24 hours of plan free.

3. To unlock full plan + push notifications + adjustments → pay $4.99 per-trip or $19/yr.

4. Stripe checkout → email with linked plan + push setup (PWA install).

**What it looks like**

• **Landing**: split hero. Left: "Most jet-lag apps work for someone else's body. Yours doesn't care about your morning meeting." Right: animated mockup hour-by-hour timeline with light/sleep/melatonin chips.
• **Main screen**: hourly timeline — bright-light icon + caffeine icon + sleep icon on each hour; bottom "mark as missed" button triggers re-adjust.
• **Output format**: PWA push notification "It's your bright-light window: get outside for 30 min" (every 1-3 hours during active protocol).

**MVP build plan (11 days)**

• Day 1-2: FastAPI + Postgres on Railway, Stripe one-time + subscription, JWT auth optional (guest-checkout OK).
• Day 3-4: Chronotype quiz + flight input form, validation, Claude Sonnet prompt engineering for structured JSON plan output.
• Day 5-6: Timeline UI (React PWA), Tailwind, Cloudflare Pages deploy.
• Day 7: PWA push notifications via Web Push API.
• Day 8: On-trip activity overlay + real-time adjust endpoint (Claude streaming, partial re-generation).
• Day 9: "Not medical advice" disclaimer in onboarding + footer + email.
• Day 10: Landing + pricing page + ProductHunt assets.
• Day 11: Smoke tests, Stripe webhook production, ship.

Source signals

• `SIG-20260504-global-health-companion-jet-lag-optimizer` — TravelAwaits 2025 confirms jet lag as universal trip-quality destroyer; existing solutions fragment into 3 inadequate buckets; UNWTO 2024 reports 700M international arrivals/year with 30-40% reporting significant jet lag impact

Reasoning

The pain signal is direct and quantified: TravelAwaits 2025 cites "jet lag can ruin a vacation in many subtle ways" as universal pain, and existing solutions segment into three inadequate buckets — generic sleep apps without flight awareness, expensive physical kits (FlyKitt $300+), and manual light-exposure calculators that demand the user understand circadian science themselves.

Why now: Claude Sonnet 4.6 can generate a structured JSON behavioral plan from 3-5 parameters (departure, arrival, chronotype, trip goal) — what required a human chronobiologist at StopJetLag six years ago is now a $0.02 API call. That's a structural shift from Timeshifter's mono-algorithm to truly personalized output.

Differentiation: (a) per-trip pricing $4.99 removes Timeshifter's subscription friction; (b) on-trip activity input ("I have an important meeting 9am day 1" vs "vacation, no meetings") changes recommendations — competitors don't have this; (c) real-time adjustment if user missed a step — Timeshifter requires manual plan restart.

Gross margin profile: $4.99 per-trip × $0.05 LLM cost = 99% gross margin. Solo build in 11 days. Zero regulatory friction provided "not medical advice" disclaimer is strictly maintained.

Quick competitive read

Direct competitors — low-to-medium density (3 named players, each with a specific weakness):

• **Timeshifter** ($9.99/mo, 6 yrs old): single-product jet-lag app; rigid one-chronobiologist algorithm; no on-trip activity input; subscription-only no per-trip option.
• **StopJetLag** ($59.95 one-time per trip, 18 yrs old): email-delivered PDF plan from human consultant; dated UI; one-shot purchase friction.
• **Sleepopolis Jet Lag Calculator** (free, 3 yrs old): web calculator; basic time-zone math; no behavioral plan; no AI.

White-space: per-trip pricing + AI personalization + on-trip activity awareness — empty.

Initial pricing hypothesis

$4.99 per-trip (one-shot, no subscription), $19/yr Unlimited (unlimited trips, re-adjustment, PDF export). 7-day free trial on Unlimited. Anchored to developed-tier consumer wellness willingness ($5-20/mo, taxonomy.yaml) and to Timeshifter $9.99/mo as ceiling — we are 50% cheaper on subscription and 2× cheaper per-trip.

Distribution hypothesis

ProductHunt launch + SEO long-tail on "jet lag calculator", "how to avoid jet lag flying to Tokyo" (low competition from consumer apps). Communities: r/solotravel, r/digitalnomad, r/business_travel — post "I built X because Timeshifter felt rigid". After 100 paying users — Twitter/X build-in-public, affiliate with travel bloggers.