IMF Calculator

Diet setup per Lyle McDonald's Intermittent Modified Fasting — RFL days, maintenance days, and weekly patterns. This calculator only covers the basics — get the book for the full method.

Your Numbers

Units

Sex (for body-fat category ranges)

Bodyweight (lb)

Body fat %

BF% comes from a DEXA scan (reads ~3–6% higher)

Daily activity (excluding formal exercise) Training during the week (sets protein) Exercise on a maintenance day

Right box = minutes per session.

Exercise on an RFL day

Maintenance-day fat intake IMF pattern

Body Composition

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Diet category

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Lean body mass

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Fat mass

RFL Day the "fasting" day

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Protein (minimum)

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Est. calories

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Est. daily deficit

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Est. fat loss / RFL day

Plus – of combined EPA/DHA (fish oil), 3–4 cups (225–325 g) of vegetables, and liberal salt/potassium (Lite-Salt). Leanest protein sources only; keep tag-along carbs and fats to ~20 g each per day. No calorie target — protein is the target.

Maintenance Day the "feasting" day

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TDEE / calorie target

Macro	Grams / day	Calories	Notes
Protein	–	–	same as RFL day
Fat	–	–	–
Carbohydrate	–	–	whatever calories remain

Swap rule: 10 g fat ⇄ 25 g carbs (~100 cal). Keep protein, EFAs and vegetables identical to the RFL day and add carbs/fats on top — a modular diet.

Weekly Plan

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RFL days / week

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Est. fat loss / week

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Weekly deficit

Days are placeholders — shuffle RFL/maintenance days freely around key workouts and social life, as long as the weekly pattern holds. Put maintenance days on your hardest training days.

Estimates follow the charts in the book (BMR by category × activity multiplier; protein by category, LBM and training; fat loss at ~3,500 cal/lb). Real-world results are always somewhat less than paper math. This is not medical advice — very-low-calorie days aren't appropriate for everyone; check with a professional, especially with any medical condition.