Health
Health Calculators
Calculator Matters’ health category covers three foundational screening and planning tools — BMI, TDEE, and a calorie-deficit timeline — each built to the same formula-transparency and worked-example standard as every other tool on this site, with clear limitations rather than a diagnosis or a guarantee. Further health and fitness calculators are planned; each one will meet this same bar before it is published, not the other way around.
Body Measurement
Energy & Metabolism
Weight Management
Who this is for
Built for anyone who wants a quick, honest BMI screening check, a realistic estimate of daily calorie needs, or an honest weight-loss timeline — in metric or US customary units — with a clear list of what each result does and does not tell you.
How to choose a calculator
Start with the BMI Calculator for a quick screening check from height and weight alone. Use the TDEE Calculator to estimate your daily calorie needs (BMR, maintenance range, and loss/gain scenarios) from the Mifflin-St Jeor equation and your activity level. Use the Calorie Deficit Calculator once you have a weight goal, to turn a percentage deficit, weekly pace, target date, or custom calorie target into a daily calorie target and an adaptive weight-loss timeline range.
Treat every result as a screening or planning estimate to discuss with a healthcare professional or registered dietitian, not a diagnosis or a guaranteed outcome.
Compare health calculators
What each calculator is best for, the main inputs it needs, what it shows, and what to keep in mind.
| Calculator | Best for | Key inputs | Shows | Keep in mind |
|---|---|---|---|---|
| BMI Calculator | A quick, honest BMI screening check with real limitations explained | Height, weight, unit system (metric or imperial), optional age and context flags | BMI value, adult category, healthy-weight range, distance from nearest boundary | Screening estimate only, not a diagnosis; adult categories do not apply under 18 |
| TDEE Calculator | Finding a realistic starting-point calorie target before setting a goal | Height, weight, age, equation reference, activity level, optional body-fat % | BMR, TDEE, maintenance range, loss/gain calorie scenarios | An estimate — activity level is the largest source of uncertainty; not intended under 18 |
| Calorie Deficit Calculator | Planning a realistic weight-loss timeline with an honest planning range | Maintenance calories (calculated or known), current/target weight, goal method (percent, pace, date, or custom) | Daily calorie target, deficit, adaptive weight-projection timeline range | A planning approximation, not the NIH Body Weight Planner; not a medically supervised diet |
Best calculator path
- Enter your height and weight in the BMI Calculator to get your BMI, adult category, and healthy-weight range.
- Use the TDEE Calculator to estimate your maintenance calories from your BMR and activity level.
- If you have a weight goal, use the Calorie Deficit Calculator to turn it into a daily calorie target and a planning-range timeline.
- If you are an athlete, pregnant, older, or living with a limb difference, read each calculator’s limitations section for how it applies less directly to your situation.
Common mistakes and limits
- Reading a single BMI figure as a full health verdict instead of one screening measure among many.
- Applying the adult category table to a child or teen — pediatric BMI uses age- and sex-specific percentiles instead.
- Treating a TDEE or calorie-deficit estimate as an exact number rather than a range with real uncertainty.
- Assuming weight loss is linear — actual progress varies with water weight, adherence, and individual metabolism, which is why the Calorie Deficit Calculator shows a planning range, not one fixed date.
When not to rely on calculators alone
BMI is a screening measure, not a diagnosis, and TDEE/calorie-deficit results are estimates, not exact measurements or guarantees. None of these tools measure body fat percentage, muscle mass, bone density, fat distribution, metabolic health, or fitness directly, and all are less representative for muscular or highly athletic people, pregnant or breastfeeding people, older adults, children and teens, and people with certain medical conditions, a history of an eating disorder, or a limb difference. None of these calculators should be used to start, stop, or adjust any medication. Discuss any health concern, and any decision about weight, diet, or exercise, with a qualified healthcare professional or registered dietitian.
Source and calculation basis
The BMI Calculator uses the standard metric (kg/m²) and imperial (703 × lb/in²) BMI formulas and the adult classification bands published by the World Health Organization and the US CDC. The TDEE and Calorie Deficit calculators use the Mifflin-St Jeor resting-energy-expenditure equation and guidance from the CDC and NIH/NIDDK on healthy weight and calorie floors. Every calculator links its own sources from its Sources and Methodology section.
See the Methodology for how calculators are built and reviewed, who runs the site, the Disclaimer for the full terms, and the Contact page to report an issue.
Frequently asked questions
Common questions about health calculators and how to use them.
What calculators are in the Health section?
Three tools: the BMI Calculator (adult classification band and an estimated healthy-weight range, in metric or imperial units, with a separate result for anyone under 18), the TDEE Calculator (Mifflin-St Jeor BMR and TDEE, a maintenance range, and calorie scenarios for losing, maintaining, or gaining weight), and the Calorie Deficit Calculator (a daily calorie target and an adaptive, week-by-week weight-loss timeline range from your TDEE). More health calculators are planned, but each one is held to the same formula-transparency and sourcing standard before it is published.
Is BMI a reliable measure of health?
BMI is a widely used screening measure based on height and weight, not a diagnosis. It can be a poor fit for muscular or highly athletic people, pregnant people, older adults, children and teens, and some other groups — the BMI Calculator explains these limitations next to the result rather than only in a footnote.
Does this section give medical advice or diagnoses?
No. Every calculator in this section is an educational screening or planning tool, not medical advice or a diagnosis. Results are meant to inform a conversation with a qualified healthcare professional or registered dietitian, not replace one.
How do the BMI, TDEE, and Calorie Deficit calculators fit together?
BMI is a quick screening check from height and weight alone. The TDEE Calculator estimates daily calorie needs (maintenance, and loss/gain scenarios) from BMR and activity level. The Calorie Deficit Calculator takes that TDEE (or a maintenance figure you already know) and turns a goal — a percentage deficit, a weekly pace, a target date, or a custom calorie target — into a daily calorie target and a realistic, adaptive weight-loss timeline range.
Where do the classification bands and formulas come from?
The BMI Calculator uses the standard metric and imperial BMI formulas and the adult classification bands published by recognized public-health authorities such as the WHO and the US CDC. The TDEE and Calorie Deficit calculators use the Mifflin-St Jeor resting-energy-expenditure equation and CDC/NIDDK weight-management guidance. Every calculator links its own sources from its Sources and Methodology section.
Explore other categories
Browse the other calculator categories on Calculator Matters.