The method
How LeanLab decides your numbers
Every number in the app — calories, protein, weekly loss rate, time to goal — comes from a small set of rules. They're listed here, in plain English, so you can see exactly what the app is doing with your data and why. None of it is magic, and none of it is guessed.
The pace you pick
Three speeds of fat loss
When you set up your goal, you choose how fast you want to move. There's no metabolic magic at any of these speeds — eating less, you lose more. The difference is how much it costs you in hunger, sleep, training quality, and life outside the gym.
Conservative
0.5% per week
Slow and almost invisible week-to-week. You barely notice the deficit; you can socialise, train hard, and sleep through the night without hunger waking you up.
Best for: You have 6+ months. You've cut before and rebounded. You'd rather not feel it.
Moderate
0.7% per week
The sweet spot. Visible weekly progress, manageable hunger, muscle still preserved. Most people should be here.
Best for: You have 3–6 months. You can plan meals and skip the odd dinner out.
Aggressive
0.9% per week
Fast. You'll feel it most days. Training quality dips around week 4 and you'll be ready for a diet break around week 8. Worth it if you have a specific deadline.
Best for: You have 6–10 weeks. You're well-trained and well-rested. You're prepared to feel hungry.
Daily calories
How much energy you eat each day.
Formula
Cut: bodyweight (kg) × 22 · Maintain: bodyweight (kg) × 35
What it is
Your calorie target is the single biggest lever for fat loss. LeanLab puts you in a moderate deficit: roughly bodyweight × 22 kcal per day for cutting, and bodyweight × 35 for maintenance. The deficit is calibrated so you lose roughly 0.5–1.0% of your body weight per week, which is fast enough to see weekly progress but slow enough to keep muscle, hair, mood and sleep intact.
How it shapes your goal
Eating under target speeds fat loss but past a point your body fights back — energy drops, training suffers, hunger spikes, and you regain whatever you lost. Eating over target slows or reverses progress. LeanLab tracks your actual intake against this target on the dashboard rings and the diet log.
Why this works
Your body needs about 22 kcal per kg of bodyweight per day to keep going at rest. Multiply that by activity and you arrive at maintenance. Subtract roughly 20% and you have a sustainable deficit that the body doesn't fully compensate for through metabolic slowdown.
Protein target
Builds and protects muscle while you cut.
Formula
Protein (g) = goal weight (kg) × 2.2 (≈ 1.0 g per lb of goal weight)
What it is
Protein is the most important macronutrient when losing fat. LeanLab targets roughly 2.2 g per kilogram of your goal weight — enough to repair muscle after training and to keep you full between meals. Goal-weight rather than current-weight scales the protein down as you lean out, so you're not eating more than you can use.
How it shapes your goal
Hitting protein every day is what separates 'lose weight' from 'lose fat'. Under-eat protein and a meaningful share of the weight you lose will be muscle, not fat — the scale will move but the mirror won't.
Why this works
Muscle is built and broken down constantly. A deficit tips that balance toward breakdown. Eating protein every few hours keeps amino acids available, which protects muscle even when total calories are below maintenance.
Fat minimum
Hormones need fat, so we set a floor.
Formula
Fat (g) = at least 50 g per day (≈ 0.7 g per kg of bodyweight as a soft target)
What it is
Fat below 50 g per day for weeks at a time disrupts the hormones that regulate testosterone, oestrogen, mood and sleep. LeanLab treats 50 g as a hard floor — go below it occasionally is fine, go below it every day is not.
How it shapes your goal
Chronic low fat shows up as low energy in the gym, worse recovery, mood dips and slower fat loss. The diet stops working faster than it should.
Why this works
Sex hormones are synthesised from cholesterol, which comes from dietary fat. Some fat is also needed to absorb fat-soluble vitamins (A, D, E, K). Below 50 g you start running into deficits in both areas.
Carbs
Whatever calorie budget is left after protein and fat.
Formula
Carbs (g) = (calories − protein × 4 − fat × 9) ÷ 4
What it is
Carbs are flexible. Once protein and fat are set, the calories that remain are filled with carbs. There's no special target — you just match the number to what's left. Higher-carb on training days, lower-carb on rest days is fine but not required.
How it shapes your goal
Carbs fuel your training. Drop them too low and your hardest sets feel harder, which means less stimulus to keep muscle. Match them to the budget and you train well even in a deficit.
Why this works
Protein and fat have non-negotiable minimums (muscle, hormones). Carbs are the variable that adjusts to keep total calories on target.
Weekly weight loss target
How fast you should be losing.
Formula
0.5–1.0% of body weight per week (Conservative · Moderate · Aggressive)
What it is
LeanLab targets 0.5–1.0% of your body weight per week. For an 80 kg person that's 0.4–0.8 kg per week. Faster than 1% and you start losing muscle alongside fat. Slower than 0.5% and most people lose patience before they see results.
How it shapes your goal
This rate is what feeds the timeline estimate. Pick conservative and the math expects 0.5% — your goal date is further out but the diet is easier to sustain. Pick aggressive and the math expects 0.9% — your goal date is closer but the diet bites harder.
Why this works
Research on dieting athletes shows that under 1%/week, muscle is largely preserved. Above that, muscle loss accelerates. The sweet spot for most people is around 0.7%/week — fast enough to feel like it's working, slow enough to keep what you've built.
Body fat percentage
The number that actually matters — not your bodyweight.
Formula
Navy formula (waist + neck + hip + height) or user-entered estimate
What it is
Body fat percentage is the fraction of your weight that is fat versus everything else (muscle, water, organs, bone). It is what most people actually mean when they say 'lean'. LeanLab estimates it two ways: the Navy circumference formula (a regression on waist, neck, hip and height) and your own estimate (from a DEXA scan, calipers, or a visual reference chart).
How it shapes your goal
Body fat % is the input to the timeline. We work out how many kilograms of pure fat you need to lose to reach your target body fat, then divide by your weekly fat-loss rate to estimate weeks-to-goal. Without a body fat %, we fall back to a weight-only estimate.
Why this works
Your weight on a scale changes for many reasons that aren't fat — water, glycogen, salt, hormones, what you ate yesterday. Body fat % filters those out and tells you whether the change is what you actually wanted.
Diet break
A planned pause after 12 weeks in a deficit.
Formula
After 12 continuous weeks cutting → eat at maintenance for 1–2 weeks
What it is
After ~12 weeks in a deficit, hormones (leptin, thyroid, testosterone) drop, and the body adapts by burning a little less energy at rest. A 1–2 week stretch eating at maintenance lets those hormones recover. You don't lose fat during the break, but you also don't gain — and when you go back into the deficit, progress resumes faster than it would have if you'd just kept grinding.
How it shapes your goal
LeanLab automatically watches the date you started cutting and surfaces a banner once you've been at it for 12 continuous weeks. Ignoring this banner doesn't stop you from progressing, but most people stall around week 14–16 if they push through without one.
Why this works
The body senses energy deficit through circulating leptin and thyroid hormone, both of which drop during a cut. Eating at maintenance for ~10–14 days restores them, which restores spontaneous activity (NEAT) and rate of fat loss when you resume.
Sleep
Sleep deprivation makes fat loss harder, sometimes impossible.
Formula
If 7-day avg sleep < 6.0 h → timeline × 1.20
What it is
Sleep less than 6 hours on average and the body shifts what it burns. In a 2010 study, people in a calorie deficit who slept 5.5 h lost mostly muscle; the same people sleeping 8.5 h lost mostly fat. Same diet, different results.
How it shapes your goal
LeanLab applies a 1.20× multiplier to your time-to-goal whenever your 7-day average sleep drops below 6 hours. This isn't punishment — it's an honest projection. Sleep more and the projection tightens automatically. The dashboard sleep card surfaces a nudge whenever the 7-day average drops below 6.5 h so you can see it coming.
Why this works
Sleep deprivation raises cortisol and ghrelin, lowers leptin, blunts insulin sensitivity, and impairs recovery from training. The combined effect is that the body resists losing fat and resists keeping muscle.
Estimated 1-rep max
What you could lift for one rep, based on what you did for several.
Formula
1RM = weight × (1 + reps / 30) (Epley)
What it is
If you bench 100 kg for 8 reps, the Epley formula estimates your one-rep max at 100 × (1 + 8/30) = 127 kg. It's a theoretical maximum — you might lift a little more or less in practice. It's most accurate in the 1–10 rep range and gets shaky beyond that.
How it shapes your goal
Your estimated 1RM is shown on each Personal Best card on the Progress tab. It's a single number that summarises how strong you are at one lift, and it makes month-over-month progress visible even when the rep ranges change.
Why this works
The relationship between weight and maximum reps is roughly linear in the lower rep ranges. Epley fits that line. Other formulas (Brzycki, Lombardi) exist and give similar numbers within a few percent.
Time to goal
Weeks until you reach your target — based on everything above.
Formula
weeks = (current weight − goal weight) ÷ (weight × loss%/week) × sleep multiplier
What it is
LeanLab's timeline takes your current weight, your goal weight, your chosen weekly loss rate, and (if you logged sleep) the sleep-penalty multiplier. It assumes you stay reasonably consistent — not perfect, but in the right ballpark week to week.
How it shapes your goal
The estimate updates every time you weigh in. If you're ahead of pace, the date moves closer; if you're behind, it slides out. Plan for the projection, train and eat for the week in front of you.
Why this works
Linear projection from a stable rate is the right model for fat loss over weeks-to-months. Day-to-day weight is noisy; the 7-day average smooths it; the weekly rate is what the timeline is built on.
How everything fits together
One picture
You set a goal weight and a pace. From your current weight, LeanLab works out your daily calories, your protein, fat and carb targets, and how many weeks it should take. As you weigh in and log meals, the projection updates: if you're ahead of pace, your goal date pulls in; if you're behind, it slides out. Sleep less than 6 hours on average and the timeline stretches by ~20%. Add 2 000 steps per day and you can usually shave a week off without touching food. Hit 12 weeks of cutting and a diet-break banner appears, recommending a planned pause at maintenance — not because you've failed, but because your body needs it to keep responding.