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Sources & method

Last updated 13 September 2026

Every number in Month6comes out of a fixed formula, and every formula has a source. Here they are, with the papers behind them. The same list is in the app, under Profile → Sources & method.

Not medical advice

Month6 is a fitness and nutrition app, not a medical service. Nothing here is medical advice, diagnosis or treatment, and no outcome is guaranteed. Talk to a doctor before changing how you eat or train — especially if you are pregnant, under 18, or living with any medical condition, injury or eating disorder.

Your six-month projection

How it’s calculated. Lean mass is projected forward month by month at a rate set by your training experience, capped by a natural fat-free mass index (FFMI) ceiling of 24–25, and turned into weight and body-fat numbers by fixed arithmetic. No model or AI invents these numbers; the same inputs always give the same curve.

What that means here. The ceiling comes from the highest FFMI values measured in athletes who had never used anabolic steroids. Rate ranges are taken conservatively — the headline curve sits at 40% of the way from the low to the high rate, not the midpoint, and female rates are set at roughly half the absolute rate. A projection is an estimate, and assumes you hit at least 80% of your plan.

Your daily protein target

How it’s calculated. Bodyweight in kilograms × a factor set by your goal: 1.8 g/kg to build, 2.0 g/kg to recomp, 2.2 g/kg while cutting.

What that means here. These sit inside the range the evidence supports for people doing resistance training — meta-analysis puts the useful ceiling near 1.6 g/kg for muscle gain, and the ISSN position stand gives 1.4–2.0 g/kg, with more while in a deficit to protect muscle. Nothing here is a medical prescription; if you have kidney disease or any condition affecting protein intake, ask your doctor first.

Your daily calorie target

How it’s calculated. The Mifflin–St Jeor equation for resting energy expenditure, multiplied by an activity factor stepped by how many sessions a week you train (1.45–1.65), then by your goal's factor: ×1.125 to build, ×1.0 to recomp, ×0.825 to cut.

What that means here. A floor is enforced in code before the number is ever shown: your target is never set below 75% of your estimated daily expenditure, no matter what your goal or a check-in adjustment asks for. Starvation targets are refused by design — including by the coach.

Estimated 1RM on your lifts

How it’s calculated. The Epley formula — weight × (1 + reps ÷ 30) — applied to the best working set of each session. Warm-up sets are excluded.

What that means here. It is an estimate of a single-rep max you never have to attempt, and it gets less accurate the more reps a set has. Validation studies put prediction equations like this within a few percent for trained lifts; Month6 uses it to show a trend over time, not to prescribe a one-rep attempt.

Weekly sets per muscle group

How it’s calculated. Working sets per muscle group over a rolling 7 days, against a target range: 10–20 sets for chest, back, shoulders and legs, 6–16 for arms, up to 12 for core.

What that means here. Meta-regression shows muscle growth increasing with weekly set volume across the range studied, which is where the 10–20 band comes from. The range is a guide for spotting a neglected muscle group, not a quota — more is not automatically better, and recovery is part of the plan.

How hard a set was (RIR)

How it’s calculated. Reps in reserve: how many more reps you could have done. 0 means you hit failure, 3 means you had three left.

What that means here. RIR is a validated way to record effort without needing a max attempt, and it is what progression uses to decide whether to add load. Your own rating is the input — Month6 never infers it.

The 7h+ sleep ring

How it’s calculated. The sleep ring closes when you log seven or more hours.

What that means here. Seven to nine hours is the recommended range for adults in the National Sleep Foundation's consensus review, so seven is the floor rather than the goal. Under-18s need more; if you regularly can't sleep, that is a conversation for a doctor, not an app.

Ages 16–17: conservative defaults

How it’s calculated. Month6 is for ages 16 and up. Under 18, the coach runs in a conservative mode: no aggressive deficits, no maximal-load prescriptions, and technique before load.

What that means here. Supervised, technique-led resistance training is considered safe and beneficial for adolescents in the NSCA's position statement; maximal lifting and aggressive dieting are not part of that. Growth and puberty change what's appropriate, so a young lifter's plan should be checked with a doctor or a qualified coach.