Every tool here pulls its multipliers from primary sources. The numbers you get are the same numbers you would get from reading a meta-analysis, only faster. Use them as a starting point, not as a substitute for working with a clinician when one is appropriate.
Protein Calculator
How much protein per day for muscle gain, fat loss, endurance, or general health. Built on the 2018 BJSM meta-analysis of 49 RCTs (Morton et al.) and the ISSN position stand on protein and exercise.
Open calculator →BMI & Waist-to-Height Ratio
WHO BMI categories paired with the Ashwell 2012 waist-to-height ratio, which outperforms BMI for cardiometabolic risk. Catches the muscular-but-flagged-overweight false positive and the normal-BMI-with-hidden-visceral-fat case.
Open calculator →TDEE & Calorie Calculator
Daily calorie needs via Mifflin-St Jeor (validated by Frankenfield et al. 2005), with an optional Katch-McArdle path when body fat percent is known. Returns BMR, TDEE, and goal-aware cut, maintain, and bulk targets.
Open calculator →Macro Calculator
Goal-aware protein, fat, and carbohydrate targets for cutting, maintenance, or bulking. Protein per Morton 2018, fat floor per ISSN, calibrated for training experience and age. Includes per-meal breakdown.
Open calculator →Body Fat Calculator
US Navy circumference method (Hodgdon & Beckett 1984, r=0.90 vs hydrostatic weighing) with explicit accuracy bands. Optional 3-site Jackson-Pollock skinfold mode for caliper users.
Open calculator →1 Rep Max Calculator
Strength estimator averaging Epley, Brzycki, and Lombardi formulas. Shows the spread, applies Reynolds 2006 accuracy bands, and includes a percentage table for hypertrophy, strength, and power.
Open calculator →Body Recomposition Planner
Combine your protein target with a small calorie deficit and a sensible training stimulus to gain muscle and lose fat at the same time.
In developmentWhy these tools exist
Most fitness calculators online are built to capture an email address or sell a supplement. The numbers they produce are often cribbed from secondary sources, padded for safety, or tuned to push you toward a product. We took the opposite approach.
Each tool here cites the studies it relies on. The defaults match peer-reviewed consensus where consensus exists, and ranges where it doesn't. The tools run entirely in your browser. We don't store your inputs, don't track your results, and don't gate the output behind a signup form.
Frequently asked questions
Are these calculators really free?
Yes. Every FitCraft calculator at /tools/ is free. There is no signup, no email gate, no upsell, and no ads. The calculators run entirely in your browser, so you can use them as many times as you want without an account.
Do you store my measurements or share my data?
No. The calculators run entirely client-side in your browser. Your weight, height, neck, waist, and any other measurement you type never leaves your device. We do not transmit, log, or store any input, and there are no tracking pixels wired to the calculators themselves.
How accurate are these calculators compared to a DEXA scan or lab test?
It depends on which calculator. The protein, TDEE, and macro calculators return evidence-based ranges grounded in peer-reviewed meta-analyses (Morton et al. 2018 in the British Journal of Sports Medicine for protein; Mifflin-St Jeor 1990 in the American Journal of Clinical Nutrition for energy expenditure). The body fat calculator uses the US Navy circumference method, which Hodgdon and Beckett 1984 validated against hydrostatic underwater weighing at r=0.90 with a standard error of 3 to 4 percentage points. None of these substitutes for a clinician-administered DEXA, BIA, or hydrostatic measurement, but among at-home methods that need no equipment, they are as accurate as the field gets.
Which calculator should I use first?
It depends on your goal. For body composition, start with the body fat calculator (or BMI plus waist-to-height as a no-tape alternative), then layer in the protein and TDEE calculators. For training, the 1 rep max calculator helps you set the right loads. For nutrition planning, run TDEE first to find your maintenance calories, then use the macro calculator to split that across protein, fat, and carbs. Most people benefit from running protein + TDEE together as the core duo.
Are these calculators medical advice?
No. The calculators are educational tools for healthy adults that produce evidence-based starting points, not personalized prescriptions. They are not a substitute for medical advice from a physician, registered dietitian, or other qualified clinician. People who are pregnant or breastfeeding, recovering from disordered eating, or who have chronic kidney disease, diabetes, or other diagnosed metabolic conditions should defer to their care team rather than to a generic web tool.
Who designed these calculators?
Domenic Angelino, MS Kinesiology, MPH (Brown University), NSCA-CSCS, ACE CPT. He is FitCraft's Chief Exercise Scientist. Domenic selected the formulas, set the multipliers from primary peer-reviewed sources, and reviewed each calculator before launch. He has been published in the Journal of Strength and Conditioning Research, Medicine and Science in Sports and Exercise, and Frontiers in Physiology, and featured in TIME, Newsweek, Forbes, and TODAY.com.
Why so many calculators instead of one?
Different questions need different math. Protein intake, daily calories, body fat percentage, and one-rep max all use different equations from different peer-reviewed sources. Combining them into a single tool would either oversimplify the math (giving worse answers) or overwhelm the interface (asking thirty inputs to fill a screen with numbers no one looks at). Each calculator does one thing well, cites the specific paper that supports it, and links to companion calculators when they are useful together.