Guesswork is where most nutrition plans fall apart. These free health calculators give you a starting number for the things people most often get wrong, and each one explains the formula behind it rather than just producing a figure.
Everything runs in your browser. Nothing gets stored, nothing gets sent anywhere and none of them ask for an email address.
Body and weight
Eight tools that need a tape measure and a scale, and tell you far more than either does alone.
Calories and macros
Start with maintenance, then split it into the macros that make up every plate.
Nutrients to watch
Five numbers most adults get wrong in the same direction, year after year.
Daily habits
Sleep, caffeine, training, drinking and noise, measured rather than guessed.
All thirty one are free, need no sign up and store nothing. Everything runs in your browser. They give general estimates and do not replace advice from your doctor or a registered dietitian.
Which Calculator to Start With
Thirty one tools is a lot to face at once. Three starting points cover most reasons people arrive here.
To lose weight. Run the calorie deficit calculator for a daily target, then the protein intake calculator so the loss comes from fat rather than muscle. Track with the weight loss percentage calculator once a week.
To check your health risk. Start with the waist to height ratio calculator, which needs one tape reading and carries a threshold health bodies endorse. Add the body fat calculator for a second view from the same tape.
To build muscle. Use the lean body mass and FFMI calculator for a baseline, then the daily calorie calculator to set a small surplus on top of maintenance.
How to Read the Numbers
Every calculator here produces an estimate rather than a rule.
Individual variation is real. Two people with identical height, weight and age can differ by 10 to 20 percent in energy needs. Muscle mass, genetics and how much you move without noticing all play a part.
Use the number as a starting point. Try it for two or three weeks, watch what happens, then adjust. Results beat formulas.
Ranges are more honest than single figures. The protein, fiber and ideal weight calculators show ranges deliberately, because that is what the research supports.
Recalculate when things change. Every 10 pounds of weight change, or whenever your activity shifts substantially.
Where the Reference Values Come From
Every calculator here is built on published figures rather than invented ones: the 2025 to 2030 Dietary Guidelines for Americans for protein, fibre, sodium and added sugar, and the National Academies intake levels for water. Body composition tools use the US Navy circumference equations, the Mifflin St Jeor equation for energy needs, and the National Institute for Health and Care Excellence bands for waist to height ratio. Nutrition figures throughout come from USDA FoodData Central, and you can check any ingredient yourself there.
Who Should Not Use These
Some conditions require the opposite of what a general calculator suggests.
Chronic kidney disease. Protein usually needs limiting rather than increasing, and fluid may need restricting too.
Heart failure. Fluid restriction is common, and swelling makes body measurements read high.
Liver disease. Protein and fluid may both need adjustment.
IBS, Crohn’s disease, ulcerative colitis or a recent diverticulitis flare. Fiber sometimes needs limiting rather than increasing.
Type 1 diabetes, or type 2 managed with insulin. Large dietary changes usually require medication adjustments.
Pregnancy. Needs shift and your provider should guide them. Body measurement tools carry no meaning during pregnancy.
Any history of disordered eating. Tracking numbers can make things worse rather than better.
Follow your doctor or a registered dietitian rather than any calculator in these situations.
What We Use Them For
Each calculator connects to articles on this site.
The macro calculator pairs with our keto cheesecake, crispy keto waffles and fudgy keto brownies, all of which list net carbs per serving.
The protein calculator pairs with our high protein smoothie recipes and 30 filling breakfast recipes.
The water calculator pairs with our most hydrating foods ranked by water content and 10 infused water recipes.
Frequently Asked Questions
Are these calculators free?
Yes. No sign up, no email required and no limits on use.
Do you store my information?
No. Everything runs in your browser and nothing gets sent to a server or saved anywhere.
How accurate are they?
They give reasonable estimates from established equations. Real needs vary between people with identical measurements, so treat any result as a starting point rather than a precise figure.
Which formulas do you use?
Energy needs use Mifflin St Jeor. Body fat uses the US Navy circumference equations. Protein uses grams per kilo of bodyweight based on current dietary guidance, and fiber uses Institute of Medicine values. Each page explains its own method.
Which calculator should I start with?
For weight loss, the calorie deficit calculator. For health risk, the waist to height ratio calculator. For muscle, the lean body mass and FFMI calculator.
Can I use these on my phone?
Yes. All of them work on mobile.
How often should I recalculate?
Every 10 pounds of weight change, or whenever your activity level shifts noticeably. Body measurements are worth checking monthly rather than weekly.
Final Thoughts on These Health Calculators
Numbers help most when you treat them as a starting point. These health calculators give you somewhere sensible to begin rather than a target to obey, and each page explains the reasoning so you can judge whether it fits your situation.
Try a number for two or three weeks, watch what actually happens and adjust from there. Talk to your doctor before making large changes, particularly with kidney disease, diabetes, heart failure or during pregnancy.
These calculators provide general estimates for healthy adults and do not replace advice from your doctor or a registered dietitian. Read our full medical disclaimer and fact checking policy.