PSMF Calculator
Estimate your daily protein, calories, and expected weekly fat-loss pace on a Protein-Sparing Modified Fast.
This tool is educational and gives estimates. For medical conditions, medication use, or a history of eating disorders, consult a licensed clinician before attempting a PSMF.
What is a PSMF?
A Protein-Sparing Modified Fast (PSMF) is an aggressive fat-loss approach built around one idea: keep protein high enough to protect lean tissue while calories, carbs, and fats stay very low. It is typically used for short, focused cutting phases, not year-round dieting.
Compared with a standard calorie deficit, a PSMF usually produces faster scale loss in the short term. The tradeoff is that food variety, training performance, and social flexibility can feel more limited.
How this calculator works
This calculator starts with your body weight and body-fat percentage to estimate your lean body mass. Then it applies a protein multiplier to produce your daily protein target. Finally, it estimates calories by adding:
- Protein calories (4 kcal per gram)
- A small essential fat intake
- A low-carb allowance (default 20g/day)
You’ll also see an estimated maintenance intake and projected weekly weight-loss rate. These projections are rough, but useful for planning.
Protein target logic
The formula uses lean mass and a higher protein multiplier as body fat decreases. Leaner individuals typically need a stronger protein signal to preserve muscle while dieting aggressively.
- Higher body-fat category: lower multiplier
- Middle category: moderate multiplier
- Leaner category: higher multiplier
Why electrolytes matter on PSMF
Low-carb intake increases fluid and electrolyte losses. If sodium, potassium, and hydration are neglected, fatigue and headaches are common. Many people quit because of this preventable mistake, not because the plan itself is impossible.
- Salt food consistently
- Prioritize hydration
- Include potassium-rich low-carb vegetables
- Discuss supplementation with a professional if needed
Practical setup for your first 2 weeks
Step 1: Hit protein first
Build meals around ultra-lean protein sources: chicken breast, turkey, white fish, tuna, egg whites, shrimp, and very lean dairy options. If protein is on target, adherence improves and muscle retention is better.
Step 2: Keep carbs low and strategic
Most carbs should come from fibrous vegetables to support satiety and micronutrients. Think spinach, lettuce, cucumbers, mushrooms, zucchini, cauliflower, and broccoli.
Step 3: Keep fat controlled, not zero
PSMF is low fat, not no fat. A small essential fat intake helps with hormone and nutrient absorption needs. Avoid “accidental fats” from oils, dressings, and snacks that can quietly double your calories.
Training during a PSMF
Keep lifting to maintain muscle, but reduce total volume if recovery suffers. A common strategy is lower volume, moderate intensity, and avoiding failure on every set. Cardio can be added, but extreme cardio plus extreme calorie restriction usually backfires.
- Lift 2–4 times per week
- Prioritize big movement patterns
- Avoid chasing PRs weekly
- Use sleep and resting heart rate as recovery checks
Who should be cautious or avoid PSMF?
PSMF is not ideal for everyone. If you are pregnant, breastfeeding, underweight, dealing with unmanaged medical conditions, or have a history of disordered eating, this approach should only be considered with direct medical oversight.
FAQ
How long should a PSMF phase last?
Most people use it in short blocks (for example, 2–6 weeks), then transition to a less aggressive deficit. The leaner you are, the shorter and more conservative this phase should be.
Can I do refeeds?
Some protocols include planned higher-carb refeeds based on body-fat category and training demands. If adherence or performance drops hard, structured refeeds may help. Keep them deliberate, not random cheat days.
What matters most for success?
Accuracy and consistency: hit protein, control hidden fats, manage electrolytes, and monitor biofeedback weekly. Fast plans reward precision.