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Intermittent fasting for iPhone

Every fast, in one ring.

Fastrr follows each fast, hour by hour, on a plan fitted to your sleep and your first meal.

Download on the App Store

Includes in-app purchases.

Fastrr’s Today screen at night: the ring at 16 hours 31 minutes, goal reached, in the Deep Fat Burn phase.

A plan that fits your day.

Answer a few questions about your goal and your day. Fastrr recommends a fasting plan, fits your eating window around your sleep and first meal, and lets you choose when your first fast starts.

Tonight20:00Tomorrow12:00

An example 16:8 plan: a 16-hour fast from 20:00, then eight hours to eat.

Plans12:12 · 14:10 · 16:8 · 18:6 · 20:4 · OMADor a custom length

Follow your fast, phase by phase.

Six typical phases, from the first hours to 36 hours and beyond, explained in plain language, with cited sources.

Today shows the phase your fast has likely reached, and what usually happens in it.

  1. Blood Sugar Drop0–4h
  2. Fat Burn Shift4–12h
  3. Early Ketosis12–16h
  4. Deep Fat Burn16–20h
  5. Growth Hormone Rise20–36h
  6. Extended Fast36h+
Phase times are typical, not measured.

Your fast, without opening the app.

A Live Activity starts with your fast and shows it on the Lock Screen and in the Dynamic Island. Widgets sit on the Home Screen, the Lock Screen and in StandBy.

On Apple Watch, see your fast and your goal, start or end a fast, or add a glass of water.

Fastrr on Apple Watch: 14 hours 3 minutes, Early Ketosis, goal at 13:43.
Apple Watch
An iPhone Lock Screen with Fastrr’s Live Activity: goal reached, 16 hours 59 minutes.
Lock Screen

The watch app needs watchOS 26 and works with Fastrr on your iPhone.

Also in Fastrr.

History
Week, month and year charts of your fasts, with your records.
Water and weight
Log water in one tap, and see your weight trend.
Apple Health
Today’s steps, heart rate, sleep and workouts, in the app.
Reminders
When it’s time to start, and when you reach your goal.
Fastrr’s History screen: a week of fasts as bars, with the average, goals reached and total.Fastrr’s Water log at night: 2.0 of 2.5 litres today, with the last seven days as bars against the goal.

Safety

Fasting isn’t for everyone.

Setup starts with a required health check and a disclaimer. Fasting isn’t recommended under 18, in pregnancy or on diabetes medication. If setup flags any of these, Fastrr asks you to check with your doctor and keeps you to gentle fasts of 14 hours or less.

Along the way there are extended-fast warnings and electrolyte reminders.

Privacy

Steps, sleep and heart rate stay on your iPhone.

What Fastrr reads from Apple Health stays on your iPhone and never reaches our servers. We don’t sell your data or use it for advertising, and you can delete your account from inside the app.

One exception: weigh-ins you import from Health are backed up to your account if you sign in.

Read the privacy policy

Fastrr

For iPhone, with an Apple Watch app

Download on the App Store

Includes in-app purchases.