What is FitUtils?
FitUtils is a free collection of health and fitness calculators built for people who want accurate, no-nonsense tools. There's no account required, no subscription, and no data sent to any server. Everything runs directly in your browser.
Our goal is simple: give you the information you need to understand your body — backed by science, presented clearly, and available to anyone with a browser.
We built FitUtils because most health calculators online require signups, use outdated formulas, or are clunky to use and uninformative. FitUtils is lean, fast, and honest about what these numbers mean.
Our Mission
Health information should be accessible to everyone. We believe that understanding your body — from your BMI to your calorie needs to your sleep — shouldn't require a gym membership, a nutritionist appointment, or a subscription to a wellness app.
Data Sources
All FitUtils calculators use formulas and reference data from peer-reviewed research and globally recognized health organizations:
WHO
World Health Organization — BMI classification standards and global health guidelines.
NCD-RisC
NCD Risk Factor Collaboration — global BMI distribution data used for percentile estimates.
CDC
U.S. Centers for Disease Control and Prevention — additional reference data for adult BMI and weight categories.
Mifflin-St Jeor
The modern default equation for Basal Metabolic Rate, behind our Calorie and TDEE calculators.
Harris-Benedict & Katch-McArdle
The classic revised equation and the lean-mass one, offered as alternatives in the TDEE calculator.
Epley, Brzycki & Lombardi
Three published one-rep-max equations, shown side by side so you can compare rather than trust a single formula.
NHLBI & AMDR
U.S. clinical guidance on low-calorie diets and the Acceptable Macronutrient Distribution Ranges — the limits our calorie and macro tools check your results against.
National Sleep Foundation
The 2015 consensus recommendations on sleep duration by age (Hirshkowitz et al., Sleep Health) — the table and the optional age control in our sleep calculator.
Aggregated reaction data
The ~273 ms median from large public samples of browser-based visual reaction tests. Our percentile and reaction-age scales are our own approximations built on it.
Hodgdon & Beckett; Jackson & Pollock
The U.S. Navy circumference equations and the three-site skinfold equations behind our body fat calculator.
FRIEND Registry
Kaminsky et al., Mayo Clinic Proceedings — treadmill VO2 max reference standards by age and sex, used for the categories and percentiles in our VO2 max tool.
Cooper, Kline & McArdle
The 12-minute run, the Rockport one-mile walk and the Queens College step test — the field protocols our VO2 max calculator implements.
Uth et al.
The heart-rate ratio method (2004) and its sex-specific proportionality factor (2005) — the no-exercise option in our VO2 max calculator.
CDC/NCHS life tables
United States Life Tables, 2023 — the actuarial baseline for our life expectancy calculator, alongside World Bank figures for the by-country reference.
NHIS & NHANES
National survey data on smoking status, physical activity and BMI — how common each answer is, which is what lets our life expectancy tool measure your habits against the national average rather than against each study's own control group.
NEJM, PLOS Medicine & The Lancet
Jha et al. on smoking, Moore et al. on physical activity and the Prospective Studies Collaboration on BMI — the three lifestyle adjustments in our life expectancy tool.
Privacy Commitment
We take privacy seriously. All calculations happen in your browser — your height, weight, and other inputs are never sent to our servers. We use IP geolocation (via ipapi.co) only to set your default unit system (Imperial for US users, Metric for everyone else), and this data is not stored or logged by us.
Read our full Privacy Policy.
Our Calculators
- BMI Calculator — Body Mass Index, category, healthy weight range, and how close you are to an ideal BMI.
- Calorie Calculator — how many calories to eat a day to lose, maintain, or gain weight, with your maintenance figure alongside it.
- TDEE Calculator — Total Daily Energy Expenditure from your basal rate and activity level, with a choice of three BMR equations.
- Macro Calculator — protein, fat and carb targets in grams, with protein set from your body weight rather than a flat percentage.
- 1RM Calculator — your one-rep maximum from a submaximal set, plus a percentage table for picking working weights.
- BMR Calculator — the energy you burn at complete rest, shown next to what it becomes at each of five activity levels.
- Calorie Deficit Calculator — daily calories for a chosen rate of loss, the weeks left to your goal weight, and a week-by-week projection.
- Sleep Calculator — bedtimes or wake-up times that land on the edge of a 90-minute sleep cycle, with a timeline of the night.
- Reaction Time Test — visual reaction speed over five attempts, with an approximate percentile and a reaction-age estimate.
- Body Fat Calculator — body fat percentage from the Navy tape method or skinfold calipers, with a sex-specific category scale and the fat/lean split.
- Pace Calculator — pace, time or distance from the other two, with split tables, equivalent race times and a pace-to-speed converter.
- VO2 Max Calculator — aerobic capacity from four field tests, placed against age- and sex-matched reference percentiles.
- Life Expectancy Calculator — an actuarial baseline adjusted for smoking, activity and BMI, with the source shown for every year added or subtracted.
Contact
Questions, feedback, or spotted an error in our formulas? Reach us at hello@fitutils.com. We read every message.