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About this tool
Daily protein floor to protect lean mass in a calorie deficit, using adjusted body weight when BMI is 30 or above.
This calculator finds the daily protein floor that protects lean mass while you are eating in a calorie deficit — the amount below which weight loss starts costing you muscle as well as fat. It uses the 1.2-2.0 g per kg bands reported for energy-restricted diets, and from BMI 30 upward it scales to adjusted body weight (ideal weight plus a quarter of the excess) rather than scale weight, which is standard clinical practice because fat tissue does not create a protein requirement. It also compares the result against the 0.8 g/kg RDA so you can see how much of a step up it really is.
Open Weight-Loss Protein Calculator on AltFTool — it loads instantly in your browser.
Enter the values you already know.
Fine-tune the options to match your scenario.
Read the result and use it in your planning or reporting.
Switches to adjusted body weight at BMI 30, so the target does not scale with fat mass.
Puts your floor side by side with the 0.8 g/kg RDA and the multiple between them.
Enter your calorie target and see the protein share and what is left for carbs and fat.
For most people in a deficit that is 1.2-1.6 g per kg of bodyweight per day, rising toward 1.8-2.0 g/kg if you also lift weights. That is roughly double the 0.8 g/kg RDA, which was set to prevent deficiency in weight-stable adults rather than to protect muscle during dieting.
Because fat mass has a very low protein turnover, so multiplying g/kg by full scale weight overstates the requirement. Clinical practice uses adjusted body weight — ideal weight plus 25% of the excess — which for a 100 kg, 160 cm woman gives about 64 kg instead of 100 kg, and a far more achievable target.
Indirectly, yes. Protein is the most satiating macronutrient and has the highest thermic effect, around 20-30% of its calories used in digestion, and it preserves fat-free mass so more of the loss comes from fat. It does not create a deficit on its own — total calories still decide whether you lose weight.
No — beyond about 2 g/kg the extra protein mostly displaces other food rather than speeding fat loss, and losing more than roughly 1% of bodyweight a week tends to cost lean mass regardless of intake. If you have kidney disease or another chronic condition, get a protein target from your doctor or a registered dietitian rather than a calculator.
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