Fern should feel like a companion helping you succeed — not a rule enforcer tracking whether you comply. Free, no account required, nothing tracked.
"Glycogen stores are running low — your body is shifting toward burning fat."
That's Fern's own in-app language, not marketing copy. A stage-aware ring, a Live Activity, and Dynamic Island support keep you oriented without turning your phone into something to check obsessively.
"Ketone production is ramping up as an alternate fuel source."
By now you've built real history. Fern logs every fast automatically — a real daily-hours chart, editable entries, and totals for the week and month, so progress is something you can actually see.
"Cellular cleanup processes are thought to increase around this point."
Miss a day and a streak freeze bridges the gap instead of resetting you to zero. Milestone badges, from 12 to 48 hours, are computed from your real fasting history — never a counter that can drift from what you actually did.
Fern+ lines your fasting window up with your actual sleep pattern, and lets you fine-tune it yourself on an interactive 24-hour dial.
Yes. Every named protocol — 16:8, 18:6, 20:4, OMAD, and 5:2 — is free, with no paywall and no trial that expires. Fully custom fasting windows, along with extras like Circadian Smart Schedule, are part of the optional Fern+ subscription.
No. Fern never asks for a sign-in, an email address, or a profile. Your fasting history lives entirely on your device — there's no backend to sign into in the first place.
16:8, 18:6, 20:4, OMAD, and 5:2 are built in as free presets. With Fern+, you can also set a fully custom fasting window by dragging the start and end times directly on the circadian dial.
No ads, no analytics SDKs, no tracking of any kind. Fern has no server to send data to — everything it knows about your fasts stays in local storage on your own iPhone.
A Fern+ feature that lines your next fasting window up with your actual sleep pattern instead of a fixed clock time, and lets you fine-tune it yourself by dragging on an interactive 24-hour dial.
Yes — an active fast shows a Live Activity on the Lock Screen and, on supported iPhones, a glanceable countdown in the Dynamic Island, so you don't need to open the app to check progress.
Only if you turn it on — it's never requested automatically. When connected, Fern reads (and never writes) your weight and sleep data to show trends alongside your fasting history.
Fern+ is a single flat monthly price shown before you ever subscribe — no promotional first-year rate that jumps later. Cancel anytime through your Apple ID subscription settings, no separate account needed.
No — it's general wellness information, not medical advice, and doesn't replace guidance from a doctor. Fern says this directly before you start, especially if you mention a health condition during setup.