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The planner gives you two FIT files. Pick by head unit:

• Garmin bundle (ZIP): the GPS route plus a target-watts number that renders on the screen as you ride, segment by segment. The full-feature path for Power Guide-capable Garmin devices (device list).
• FIT Workout: one structured workout, watts targets only, one step per 90-120 s split with a ±5 % tolerance band. No route on the screen. Loads on any head unit that reads FIT workouts: Wahoo Roam / Bolt / Elemnt, Hammerhead Karoo 2 / 3, Bryton Rider, and any Garmin Edge (including the older 520 / 820 that can't read Power Guide).

If your Edge supports Power Guide, take the bundle. Otherwise the Workout is the universal fallback.

USB sideloading is the only path that keeps the watts overlay. The Garmin Connect web upload and Garmin Express both re-save the file and lose the overlay (why), so drag-drop the files onto the device directly:

1. Unzip the bundle. It contains course_YYYY-MM-DD.fit and power_guide_YYYY-MM-DD.fit.
2. Plug the Edge into your computer with the supplied USB cable. It mounts as a regular drive (called GARMIN on macOS and Windows).
3. Drop both .fit files into GARMIN/NewFiles/.
4. Eject, disconnect, then power-cycle the Edge. It picks them up on next boot and moves them into GARMIN/Courses/.

On the Edge, go to Navigation → Courses, find the course (named after your route), and tap Ride. The Power Guide overlay appears as a native data field showing the target watts for the current segment, with a colour band that flips when you drift outside the ±5 % tolerance.

If your device isn't on the Power Guide list, it loads the route but not the watts overlay. Use the FIT Workout instead.

On Fenix / Forerunner / Epix watches the procedure is the same: the watch mounts as a GARMIN drive over USB, drop the two FIT files into GARMIN/NewFiles/, eject, and pick the course from Navigation → Courses on the watch.

• Wahoo Roam / Bolt / Elemnt. Open the Wahoo app on your phone, tap the workout icon → Plans → Import workout file (or share-sheet the .fit file from email / iMessage into the Wahoo app). The workout shows up under Workouts on the head unit. Pair the power meter, hit Start workout, and the device counts you through the steps with watts targets per interval.
• Hammerhead Karoo 2 / 3. Drag the .fit file onto the Karoo over USB into Workouts/, or upload to a coaching platform that syncs (TrainingPeaks, intervals.icu) and let the Karoo pick it up. Workouts menu on the device, select, start.
• Bryton Rider. Sideload the .fit file via the Bryton app or USB into the workout folder. Workout menu on the device.
• Older Garmin (any pre-Power-Guide Edge or watch). Same USB drag-drop as the bundle, but the workout goes into GARMIN/Workouts/ instead of Courses/. Training → Workouts → Choose Workout.

The Workout carries no GPS. You ride the route on whatever map you already loaded, and the device counts the power targets in parallel. Pair it with the GPX you loaded for navigation.

Power Guide is a Garmin Connect feature; the bundle's per- split watts overlay only renders on Power Guide-capable Garmin devices. Other head units (Wahoo, Hammerhead, Bryton, older Garmins) read the FIT Workout download instead: same per-split power targets, no GPS overlay.

Compatible families (Garmin's published list, 2026):

Older Edges (520, 820, 530, 830, 1030, 1030 Plus) and pre- Power-Guide watches load the Course track but don't render the watts overlay. Use the FIT Workout download instead.

Three things to check before blaming the model:

1. FTP. Was the value you typed current, or last year's? Stale FTP is the single biggest source of error in the cohort.
2. CdA. The 0.40 default is amateur-in-drops. Run bpm calibrate on a flat tempo ride to pull it within ~0.02 of truth, or use a wind-tunnel value if you have one.
3. Effort. 1.0 means "at your ceiling, every watt available". Mid-pack sportive is 0.85; gruppetto is 0.70.

After that, the honest gaps live on the methodology page (crits, bunch-tow, deep wet cobble). Honest gaps →

If it's still off, donate the ride via the Analyzer with a comment about what looked wrong. The FIT is stripped and anonymised before it hits the cohort. Never paste a raw FIT into a GitHub issue: that's a privacy leak you can't take back. Donated rides are how the model gets fitter.

Copy the planner URL. Every input (route, FTP, weight, CdA, effort, intent, sex) is in the querystring, so the link reproduces the run on the other side.

Custom-uploaded courses use a separate share flow: the AES decryption key lives in the URL fragment (the part after #), which browsers don't send to the server. Only someone with the full link can decrypt the route. The server stores ciphertext, never sees your route in plaintext. Privacy →

No. The whole model is power-balance physics: it solves for power against drag, rolling resistance, gradient. Without a measured FTP, the ceiling number is a guess and so is the prediction.

Nothing, and free forever. The library is open source (MIT); the hosted web app is free: no ads, no subscription, no paid tier. Email sign-in is only needed to download the Power Guide FIT or upload a ride, so abuse isn't anonymous.

Anonymous usage analytics via self-hosted PostHog (which pages get hit, which downloads succeed, which API calls error). No PII. The hashed email never touches the analytics stream.

Hosting is out of pocket on Scaleway: a couple hundred euros a month, so under heavy load it may throttle or briefly stop working. If it ever stops being viable, the library + Docker compose run locally, no lock-in. Privacy →

Not to plan a route or see a prediction. The planner form works anonymously. Sign-in (email magic link, no password) is needed only to:

• Download the Garmin Power Guide FIT for your Edge.
• Upload a past ride to the analyzer.
• Upload a custom GPX (the encrypted BYO-course flow).

That's it. No newsletter, no marketing follow-ups. Email is one-way hashed in storage; the address is never displayed back.

Not needed to ride. Here for anyone curious about how the files are built.

• The bundle ZIP holds two FITs: a Course FIT (GPS track, named alerts at every named cobble or gravel sector and food station, Virtual Partner pacing) and a Power Guide FIT (the per-split target-watts overlay). Both carry the same course_pk, which is how the device pairs them once both are loaded.
• The watts overlay rides in Garmin's Power Guide FIT messages, 352 and 353. Only Power Guide-capable firmware reads them; other units ignore those messages and show the track alone.
• Loading over the Garmin Connect web upload or Garmin Express re-saves the file and drops messages 352 and 353, which is why the overlay disappears if you don't sideload over USB.