Protein Calculator

The U.S. Institute of Medicine's Recommended Dietary Allowance (RDA) for protein is 0.8 grams per kilogram of body weight per day for sedentary adults — this is the minimum intake needed to avoid a gradual loss of body protein, not necessarily the amount that supports optimal body composition or muscle health. A randomized controlled trial that overfed healthy, sedentary adults diets containing 0.7, 1.8, or 3.0 g/kg/day of protein found that the low-protein group actually lost a small amount of lean body mass despite gaining weight, while both higher-protein groups gained lean mass — suggesting the RDA floor is lower than what benefits body composition even for people who aren't training.

For people doing regular resistance training with a goal of building muscle, a systematic review and meta-analysis pooling roughly 49 studies on protein supplementation and resistance-training outcomes found that gains in muscle mass and strength plateaued around 1.6 g/kg/day, with the analysis's upper confidence interval extending to about 2.2 g/kg/day — the range this calculator uses for the Active/Muscle Building tier.

The same 1.6–2.2 g/kg/day range is commonly recommended during a calorie deficit as well, to protect lean mass while losing fat. A randomized trial in exercising adults during a marked energy deficit found that a group eating 2.4 g/kg/day of protein gained lean mass and lost more fat than a group eating 1.2 g/kg/day, supporting the idea that protein needs — if anything — trend higher, not lower, while cutting.

Older adults face a different problem: anabolic resistance, a reduced ability to build muscle protein from a given amount of dietary protein, which raises the minimum intake needed to maintain muscle mass and function. The PROT-AGE Study Group's position paper recommends adults over 65 average at least 1.0–1.2 g/kg/day, with higher intakes — up to roughly 1.5 g/kg/day or more — advised for those who are physically active or managing an acute or chronic illness.

Sources:

Institute of Medicine (2005). Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. National Academies Press.
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Bray, G.A., et al. (2012). Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition During Overeating: A Randomized Controlled Trial. JAMA, 307(1), 47–55.
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Morton, R.W., et al. (2018). A Systematic Review, Meta-Analysis and Meta-Regression of the Effect of Protein Supplementation on Resistance Training-Induced Gains in Muscle Mass and Strength in Healthy Adults. British Journal of Sports Medicine, 52(6), 376–384.
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Longland, T.J.M., et al. (2016). Higher Compared with Lower Dietary Protein During an Energy Deficit Combined with Intense Exercise Promotes Greater Lean Mass Gain and Fat Mass Loss: A Randomized Trial. American Journal of Clinical Nutrition, 103(3), 738–746.
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Bauer, J., et al. (2013). Evidence-Based Recommendations for Optimal Dietary Protein Intake in Older People: A Position Paper from the PROT-AGE Study Group. Journal of the American Medical Directors Association, 14(8), 542–559.
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