Physique Forecast
See exactly where your body is headed — and what a beer on Friday or a skipped Tuesday lunch really costs you.
Not a calorie formula with a fudge factor. It runs the actual Protokl workout algorithm through a simulated body and a physiology model calibrated against real training data — then projects muscle and fat, week by week. Free, no signup.
The stuff other calculators pretend doesn't exist. This is what actually decides your results — drag them to match how you really train and eat.
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Protokl builds personalized workout and nutrition plans around your body composition, goals, and experience level. Science-backed. AI-powered. Syncs with Apple Health.
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Five models, one forecast
Most calculators multiply your weight by a number. This one runs a full simulation — the same system the Protokl app uses internally. Here's the pipeline every forecast goes through:
- 1
Your real workout algorithm
The exact recommendation engine from the Protokl app generates the daily workouts — the same progressive-overload, periodization and recovery logic real users get.
- 2
A training simulator runs the whole block
A simulated lifter performs those workouts day by day for weeks — logging every set, accumulating fatigue, and recovering between sessions exactly like the app tracks it.
- 3
A physiology model decides what the body can really do
Muscle and strength adapt at true physiological rates set by your training experience and recovery — so the lifter can only lift what a real body could. Calibrated against real 12-week training data to within half a percentage point on the main lift.
- 4
Your recommended diet is partitioned into muscle vs fat
Each week your Protokl calorie and protein targets meet an energy-balance model. Realized muscle is the smaller of what training can build and what the diet can fuel — whatever energy is left over becomes fat.
- 5
Then your real life adjusts it
Alcohol adds calories and blunts muscle protein synthesis; skipped meals cut intake and protein. Toggle them and watch the trajectory change — so you see what actually happens, not a best-case fantasy.
Straight talk on accuracy: the strength side is tightly calibrated against real data. The body-composition side is a directional, population-average estimate — individual metabolism and, above all, adherence vary — so the most reliable read is the difference between your current habits and a dialed-in version of the same plan.
Why “Eat Light All Week, Drink on the Weekend” Keeps You Lean but Skinny
It is one of the most common real-world patterns: skip lunch through the week, bank the calories, and spend them on Friday and Saturday. On the scale it looks disciplined — your weekly average intake stays moderate, so you do not get fat.
But body composition is not decided by weekly average calories alone. Muscle is built on training days, in a fed state, with enough protein and good recovery. Under-eating on those days starves muscle protein synthesis exactly when it matters, and weekend alcohol blunts recovery for a day or two after. The result: your body has just enough energy to hold what it has, but not enough of the right inputs at the right times to build. You stay lean and stall.
The fix is rarely “eat more” in bulk — it is redistributing intake toward training days, keeping protein high every day, and pulling back the alcohol. The forecast above shows how much muscle that is worth for your numbers.
How the Forecast Works
Each week the model derives your recommended calories and protein from the Mifflin-St Jeor equation and your goal, computes your energy balance, and partitions it into muscle and fat. The key rule: realized muscle is the smaller of what your training can build (capped at physiological rates by training experience) and what your diet and protein can fuel — whatever energy is left over becomes fat. Alcohol adds calories and blunts muscle building; skipped meals lower intake and protein.
This is the same body-composition engine Protokl uses internally, calibrated against real training and scale-weight data. It is a directional, population-average projection — useful for comparing choices, not for predicting a single week to the ounce.
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Frequently Asked Questions
Does alcohol really affect muscle gain?
Yes, on two fronts. Alcohol adds calories (~100 per standard drink) that push your energy balance toward fat storage while suppressing fat oxidation. More importantly, drinking around training blunts muscle protein synthesis — studies show acute reductions of roughly 25-35% when alcohol is consumed after a workout — and it degrades the sleep and recovery that muscle growth depends on. You can drink and still make progress, but heavy weekend drinking measurably slows muscle gain and worsens your muscle-to-fat ratio. This calculator models that cost directly.
I skip lunch to stay lean while I drink on weekends. Is that a problem?
It is a classic trade-off. Under-eating on weekdays offsets weekend alcohol calories, so your weight and fat stay controlled — which is why it feels like it works. But it also means you spend training days under-fed and low on protein, exactly when your muscles need fuel to grow, and the alcohol blunts recovery on top of that. The net result is that you can stay lean while barely building muscle. If your goal is body composition rather than just weight, spreading protein across the day and cutting the alcohol does far more than the scale suggests.
How accurate is a body-composition forecast?
Treat it as a directional, population-average projection — not a precise week-by-week prediction. Real TDEE varies ±10-15% between individuals, and day-to-day scale weight is dominated by water and glycogen, not tissue change. The value is in the comparison: how your muscle and fat trajectories differ between habits, and what a given change (less alcohol, more consistent meals, a different surplus) is worth. The engine here was calibrated against real 12-week training and scale-weight data, predicting the demonstrated bench trajectory to within half a percentage point.
How much muscle can I realistically build?
Natural muscle gain is slower than most expect and depends heavily on training age. Beginners can add roughly 1-2 lbs of muscle per month in year one, intermediates about 0.5-1 lb per month, and advanced lifters as little as 0.25-0.5 lb per month even with everything optimized. The forecast caps lean-mass gain at these physiological rates, so scale gains beyond them show up as fat — which is exactly why an aggressive surplus does not build muscle faster, it just adds fat.
What is the difference between this and a normal calorie calculator?
A standard calculator gives you a single calorie and macro target assuming you follow it perfectly and live like a monk. This tool projects the actual body-composition outcome over time and lets you dial in the two variables that quietly determine most peoples results — alcohol and meal consistency — then shows the muscle and fat difference between your real habits and a dialed-in version of the same plan.