Coming to iPhone
Your watch says 3 140. You burned 2 610.
Realburn finds your real calorie burn, with or without a watch. It checks every number against your scale, so your deficit is the one you actually have.
Know your numbers? See what you really burn with the calculator
The problem
The calorie number you trust is a guess.
The average error of Apple Watch calorie estimates, across 56 studies. Heart rate was off by 4%, steps by 8%.
Choe and Kang, Apple Watch accuracy in monitoring health metrics, Physiological Measurement, 2025.
Apple Watch calorie estimates are off by 28% on average.
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Your watch
Guesses your burn from your heart rate and movement, with a model built for the average person. On a big day it can add hundreds of calories you never burned.
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Activity apps
Add up what the watch says and believe it. If the watch is off by 500, so is your deficit.
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Diet apps
Ignore the watch and learn your burn from your weight. Accurate, but slow, and only if you log every meal.
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Realburn
Puts the watch next to the scale. Your weight trend shows what you really burned, and Realburn learns how far off your watch is, then corrects every day after.
How it works
Start with your phone. Every step makes the number more exact.
Realburn reads Apple Health and shows how sure it is of every number. Add a source and the range gets narrower.
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01 Estimate · ±12%
Just your iPhone
Your resting burn from age, sex, height and weight, plus the steps and workouts your phone records, plus digestion.
Example: between 2,300 and 2,920 kcal, most likely 2,560.
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02 Good
+ a scale
Weigh in, even once a week. Your weight trend shows your real deficit, and roughly how much you eat, without logging a thing.
Example: between 2,450 and 2,760 kcal, most likely 2,590.
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03 Calibrated
+ the food you log
In any app that writes to Apple Health, or with Realburn’s Quick Log. Food in, weight change out: your real burn, as one number.
Example: 2,610 kcal, checked against the scale.
It makes the burn finer, minute by minute instead of step by step. Realburn checks it against the scale like any other source and tells you how far off it is.
Example numbers, for illustration.
Works without a watch
No watch? No food log? Still a real number.
No watch
Your iPhone is enough
Realburn has its own burn model. It doesn’t copy a device’s number; it builds yours from your body, your steps and your workouts, and shows the range honestly while it learns.
No food log
Quick Log, in five seconds
No food database, no barcodes. Type a number, tap a meal you saved once, or pick a size. Logging doesn’t need to be exact, only consistent.
Three weeks, then stop
Calibrate once, keep the number
Log roughly and weigh in each morning for 21 days. Realburn learns your personal factor, like “your body burns 9% less than the formula”, and you can stop logging. Your daily burn stays calibrated, and the scale keeps checking it.
Privacy
Your body’s data stays on your iPhone.
- No accountNo sign-up, no password, no profile on a server.
- Calculated on your phoneYour weight, food and activity are read from Apple Health and processed on the device. They never leave it.
- No ads, no trackingHealth data is never used for advertising or sold. Not now, not later.
Questions
FAQ
When does Realburn launch?
Realburn is in development for iPhone. Join the waitlist and you’ll get one email on launch day.
Do I need an Apple Watch?
No. Realburn works with just your iPhone. A watch or ring makes the activity part finer, and Realburn checks it against your scale.
Do I have to log my food?
No. With a scale, your weight trend already shows your real deficit and roughly how much you eat. Logging, in any app or with Quick Log, is what gets you to a single calibrated number, and three weeks of it is enough.
How can Realburn know my watch is wrong?
Energy doesn’t disappear. Over a few weeks, the food you ate minus the change in your weight tells how much you really burned. Realburn compares that with what your watch reported for the same days and works out your watch’s personal factor, like ×0.83.
Every number comes with its precision, so you always know how sure it is.
Which apps and devices does it work with?
Anything that writes to Apple Health: Apple Watch and other watches or rings, smart scales, and food apps like MyFitnessPal, Cronometer, MacroFactor or Yazio. Realburn also catches sources that count the same calories twice.
Will it be free?
Your daily burn and your balance, deficit included, will be free. A Pro upgrade will add calibration and long-term trends.
Is it on Android?
No. Realburn is built on Apple Health, so it’s iPhone only.
Is this medical advice?
No. Realburn gives estimates for healthy adults. If you have a medical condition or an eating disorder, follow your doctor’s guidance.