FatForecaster

Measure the same way every time. The app reads change over time, so you want two readings to differ only because your body changed.

• Weight: weigh every morning, after the toilet and before you eat or drink. Use the same scale on the same hard floor, in the same clothes or none.
• Weigh daily, not weekly. One reading can swing by a kilo or more from water, salt and food. The 7-day trend smooths this out if it has enough readings.
• Waist: stand relaxed and measure on bare skin at navel level, with the tape level with the floor. Keep it snug without denting the skin. Breathe out normally, then read it.
• Neck (Navy method only): measure just below the Adam's apple, with your shoulders relaxed and the tape sloping slightly down at the front.
• Hips (Navy method, when asked): measure at the widest point, with your feet together.

Take each tape measurement two or three times and use the average. With waist-based formulas, one centimetre makes a real difference.

Re-measure your body every 4 to 6 weeks, the same interval as the reminder in Settings. Do it at the time of your morning weigh-in, and not straight after a big meal or a workout.

The app compares how your weight changed with what you logged eating over the same days. That's how it tells a real deficit from ordinary day-to-day noise.

Two weeks is about the shortest stretch that gives a reliable signal. With less, a forecast would mostly be a guess, so the app waits.

Food-logging apps such as MyFitnessPal often don't have your local product. They offer similar items from other brands, or a generic entry.

The lowest-calorie option is tempting. If you always pick it, you under-log what you really eat, and the gap adds up over every meal.

Pick the highest-calorie option that is still plausible. Logging a little too much on an uncertain item affects your numbers far less than a habit of logging too little.

• Current trend is your trend weight, a 7-day moving average of your logged weight. Every calculation in the app uses it, never a single scale reading.
• Estimated body fat % is not a new measurement. The app works it out from your trend weight and the lean mass from your last re-measurement. It drifts a little between re-measurements and resets when you record a new one.
• Recalibrated TDEE, on the Review tab, is your real average daily burn. The app calculates it from what you logged eating and how your weight changed over the last 14 days. It ignores the burn figures you log.
• Forecast date and the days-remaining range come from your recalibrated TDEE, your trend weight and your target weight. The range narrows as you log more days.

If you eat as much as your recalibrated TDEE or more, there's no deficit to project. The app tells you that instead of guessing a date. If you eat clearly more, it tells you you're moving away from your goal.

• The solid Logged line is your estimated body fat % on each day you have data.
• The dotted Forecast line carries that pace forward to your target. It curves because your lean mass, and with it your daily burn, slowly goes down as you lose weight.
• The shaded band shows how far the forecast date could move if your consistency changes. It's wider when your logging is less consistent.
• The dashed horizontal line is your target body fat %.
• The Original plan line keeps the first forecast date the app could calculate, so you can see if you're drifting from it. It appears after your first day that counts as a real deficit.

The forecast never uses your logged burn to decide whether you're in a deficit. That includes burn from a wearable or the Health app.

It relies on two things it trusts more: what you logged eating, and what your weight did over the same two weeks. If those don't match burn minus intake, the app believes your weight.

Common reasons for the gap:

• Wearables often overestimate burn, especially active calories.
• If you lift weights, you can lose fat while you gain muscle. The scale stays flat while you make progress.
• Food is easy to under-log. Portions are hard to judge, snacks get forgotten and a big weekend adds up.
• Water and glycogen change from day to day. The 7-day trend smooths this but can't remove it.

The app averages 14 days of intake, so one heavy day moves the average more than most people expect. One big weekend can cancel out a careful week.

The Review tab shows the gap directly: your logged burn next to your recalibrated TDEE.

To check your real progress, re-measure your body fat %. It reads your body composition without relying on the scale or a burn estimate.

The default estimate uses your height, weight and waist. Its formula was fitted against real DEXA scans from a large general-population sample and stayed accurate across many body shapes.

The Navy method, a formula from 1984, uses your neck and waist. It treats neck size as a sign of how muscular you are. That works for a typical build, but it has known blind spots:

• If your waist is large for your weight, the Navy method often underestimates your body fat by a lot.
• A very muscular neck can make it overestimate.

If you've had a DEXA scan, InBody, BodPod or caliper reading, enter that number in New body fat %. A real scan beats any formula.

If an estimate doesn't match what you see in the mirror or in progress photos, trust your eyes. Tape-based methods have this known limit. It doesn't mean anything is wrong with you.

When you lose weight, some of it is usually lean tissue as well as fat. This setting controls how much of the weight you lose counts as fat. That changes the target weight for your target body fat %.

The guide in Settings suggests a starting point from your training frequency, your protein intake and your waist and hip trend if you've measured it. You can also set the ratio yourself.

A re-measurement corrects your lean-mass baseline. Your weight and calorie history is still valid, but the app now reads it differently.

So the app recalculates every earlier day straight away. Old, outdated estimates don't stay on the chart.

No. There are no accounts and no servers. Everything you enter is stored only on your iPhone, and the app contains no analytics, ads or trackers.

The privacy policy lists everything the app stores.

No. You can type everything in yourself. If you connect the Health app, FatForecaster reads your weight, calories eaten, protein and calories burned. It never writes to Health.

To stop, open the Health app and go to Sharing › Apps › FatForecaster, or tap Disconnect in the app's Settings.

To back up, export a backup from Settings. The app hands the file to your share sheet, and you choose where it goes.

To clear your daily logs, tap Erase all logged history in Settings. Deleting the app removes all of its data.