How to use iFast, in the order that works

Day one: start a fast, ignore the rest

The most common way to fail at this is to spend your first evening configuring an app instead of fasting. Every screen you set up before you have fasted once is a decision made without information.

Before you do: fasting is not for everyone. If you are pregnant or breastfeeding, under 18, take insulin, a sulfonylurea or anything that has to be taken with food, take blood-pressure medication, or have ever had an eating disorder, talk to a doctor first rather than starting today.

With that said: open the iFast tab, pick a window, press start. If you are new to this, 12:12 or 14:10 is the honest place to begin. 12:12 sounds trivial and is not, if you currently eat from 7am to 11pm. 16:8 is the default for a reason, but starting there and quitting in week two beats nothing only in the sense that both produce no result.

The timer runs whether or not the app is open, survives a restart, and does not need your phone unlocked. There is nothing to babysit.

The ring fills as the hours pass and its colour tracks which metabolic zone you have reached, with the named stage shown further down the screen. Once you have finished your first fast, the ring changes job: between fasts it counts how long since the last one ended, which is the number most people find changes their thinking, because it makes the eating window visible instead of theoretical.

The first week: let the streak do the work

A fast counts toward your streak if you reach 80 percent of your goal. Not 100. If you set 16 hours and finish at 13, that day still counts.

This is deliberate and it is the most important thing to understand about the app. A streak that resets to zero on a single miss is the mechanic that turns one bad day into quitting altogether. Here one miss in any rolling seven-day window is forgiven, and today never breaks your streak, so you always have the rest of the day to fix things.

You also earn a freeze for every seven days of streak, up to three saved. A freeze covers a day you did not fast at all. Life happens, and it should not cost you anything.

Practically, this means you should set a window you can hit on a normal Tuesday rather than your best day. The forgiveness is there to absorb the exceptions, not to be your plan.

Week two: start logging one thing

Not everything. One thing. The most useful first log is whatever you are most curious about, because curiosity is what makes you keep doing it.

For most people that is water, because it is the easiest to log and the fastest to change. Tap the Charts tab, hit the plus, pick Water, and type the amount. You can type an exact number rather than picking from preset buttons, and you can set the time it actually happened if you are logging after the fact.

Weight is the other reasonable starting point, with one caveat: weigh yourself at the same time of day, and ignore any single reading. The first fortnight of any eating change moves a couple of kilograms of water and glycogen, which tells you nothing about fat.

If you have an Apple Watch or carry your phone, connect Apple Health in Settings and steps arrive on their own. That is the highest-value setup step in the app because it costs one tap and then keeps working.

Week three: look at the charts, but look at the right one

The chart that matters is not the one you expect. It is the five-week grid on the Fasting card, which shows which days you fasted and whether you hit your goal.

Length is the number people fixate on, and consistency is the one worth watching. The grid makes your actual pattern impossible to argue with, which is uncomfortable for about thirty seconds and useful thereafter. Most people discover they are a weekday faster who thought they were a daily one.

The Avg fast and Goal hit chips above it give you the same story in two numbers. If your goal-hit rate is under about half, your window is too ambitious rather than your willpower being insufficient. Shorten it. A 14-hour fast you actually do beats a 16-hour fast you abandon.

When the coach becomes useful, and when it does not

The Coach tab has two halves and they suit different moments. Today builds you a plan around your fasting window: when to eat, roughly what, hydration and movement cues. Chat can pull your recent fasts, weight, hydration, steps and Apple Health data into an answer.

Do not start here. A day plan built before the app knows anything about you is a generic day plan. It becomes genuinely useful once you have a fortnight of logs, because then it is reasoning about you rather than about an average person.

The chat is most useful for the specific awkward question rather than the general one. "Why am I hungry at 3pm" gets a better answer than "how do I lose weight", because the first is answerable from your data and the second is not.

You can swap any meal or workout block in a plan that does not fit your day. It is worth doing rather than abandoning the whole plan, which is what most people do the first time something in it is wrong.

The order, condensed

If you take one thing from this: the app is designed to be adopted in layers, and adopting it all at once is the main way people bounce off it.

The parts people miss

The widget. It puts your fast on the home screen so you can see it without opening anything, which removes the main friction in checking.

Editing. Weight, water, meals, steps and completed fasts can all be corrected or deleted: open the relevant chart and tap Edit entries. Workouts brought in from Apple Health can be deleted but not edited. A tracker you cannot correct becomes a tracker you stop trusting, and then stop using.

The Tools tab. TDEE, BMI, body fat and a hydration target, each linking out to the research behind the formula. Worth ten minutes once, not worth checking weekly.

And the notification settings. Reminders are on by default because they help most people; if they do not help you, turn them off in Settings and they will stay off.