Health & Fitness Calculators — Free Complete Toolkit (2026)
TL;DR
This page bundles every free health and fitness calculator on UtilDaily — 9 tools across six life-area categories (body composition, energy & metabolism, cardio & training, nutrition, sleep, reproductive health) plus 8 in-depth guides. Formulas sourced from NIH, ACSM, AHA, and USDA. All calculators run 100% in your browser; no sign-up.
How do I measure body composition — BMI and body-fat percentage?
Body Mass Index (BMI) and body-fat percentage are the two most common quick measures of body composition, and they answer different questions. BMI screens populations cheaply (weight ÷ height²); body-fat percentage tells you what fraction of your weight is fat versus lean tissue. Use them together — never one alone — to read your numbers honestly.
BMI & BMR Calculator
Calculate BMI, BMR, and daily calorie needs with metric/imperial support.
Body Fat Calculator
Estimate body fat percentage using the US Navy circumference method. Shows healthy ranges by gender, ACE classification, and comparison to BMI.
Related guides
How many calories should I eat per day?
Total Daily Energy Expenditure (TDEE) is your maintenance calorie target — the number of calories you burn in a typical day. Eat below it to lose weight, above it to gain. The Mifflin-St Jeor equation gives the most accurate estimate for healthy adults. Aim for a 500 kcal/day deficit for ~1 lb/week fat loss, or a 250 kcal/day surplus for lean muscle gain.
TDEE Calculator
Calculate your Total Daily Energy Expenditure (TDEE) and BMR using the Mifflin-St Jeor equation. Get calorie targets for weight loss, maintenance, or gain.
Calorie Deficit Calculator
Calculate your daily calorie deficit for weight loss using the Mifflin-St Jeor formula. Get your BMR, TDEE, and timeline to reach your goal weight.
What heart rate should I train at — and at what pace?
Cardiovascular training is most effective when you spend time in specific heart-rate zones tied to your maximum HR. Zone 2 (60–70% of max) builds aerobic base; Zone 4 (80–90%) builds threshold; Zone 5 (90%+) builds VO2 max. Pair zone training with a pace target — minutes-per-mile or minutes-per-km — to translate effort into race times.
Heart Rate Zone Calculator
Calculate your 5 heart rate training zones based on age and resting heart rate. Supports both the standard percentage method and the Karvonen formula.
Running Pace Calculator
Calculate running pace, finish time, or distance from any two inputs. Supports min/km and min/mile. Includes race split projections for 5K through marathon.
How much protein do I actually need?
The 0.8 g/kg/day RDA is the minimum to prevent deficiency in sedentary adults — not the optimum for an active person. Strength athletes typically need 1.6–2.2 g/kg/day, endurance athletes 1.2–1.6 g/kg/day, and older adults 1.0–1.2 g/kg/day to preserve muscle. Use this calculator with your weight, activity level and goal to get a personal target.
How do I time sleep around 90-minute cycles?
A full sleep cycle takes about 90 minutes — through light sleep, deep sleep, and REM in sequence. Waking at the start of a cycle (rather than mid-deep-sleep) leaves you alert; waking mid-cycle causes the heavy, disoriented feeling called sleep inertia. The calculator works backward from your wake time and recommends bedtimes that land at cycle boundaries.
How do I find my fertile window?
Ovulation typically occurs 14 days before the next period — not 14 days after the last period — which means cycle length matters. The fertile window is the five days before ovulation plus the day of ovulation. Cycle-length variability and individual physiology mean these calculators are estimates, not diagnostics; consult a clinician for fertility planning.
Quick reference: pick the right calculator
| If you want to know… | Use this calculator | Formula source |
|---|---|---|
| My weight category | BMI & BMR Calculator | WHO / NIH |
| My body-fat percentage | Body Fat Calculator | U.S. Navy circumference method |
| My maintenance calories | TDEE Calculator | Mifflin-St Jeor (1990) |
| My weight-loss target | Calorie Deficit Calculator | USDA DRI |
| My five training heart-rate zones | Heart Rate Zone Calculator | Karvonen / ACSM |
| My target race pace | Running Pace Calculator | ACSM running formulas |
| My daily protein target | Protein Calculator | USDA RDA / ISSN guidelines |
| When to go to bed | Sleep Calculator | NIH sleep cycle research |
| My fertile window | Ovulation Calculator | Calendar method (HHS OWH) |
Frequently asked questions
Are health calculators accurate enough to make medical decisions?
No. Online calculators give population-level estimates from formulas like Mifflin-St Jeor, Karvonen, or BMI = kg/m². They cannot account for medical conditions, medications, body composition outliers, or individual physiology. Use them to understand the math and set rough targets — never as a substitute for advice from a clinician, registered dietitian, or certified trainer.
Why are BMI categories controversial for athletes?
BMI was developed to study populations, not individuals. It does not distinguish muscle from fat — so a 5'10" 200 lb athlete with 12% body fat lands in the 'overweight' BMI category despite being lean and healthy. For trained individuals, body-fat percentage and waist-to-height ratio are more meaningful than BMI alone.
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is the calories you would burn if you stayed in bed all day — pure life support. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor (1.2 sedentary up to 1.9 athlete) to reflect movement, exercise, and the thermic effect of food. TDEE is the number you actually plan meals around.
How big should my calorie deficit be for weight loss?
A 500 kcal/day deficit produces roughly 1 lb (0.45 kg) per week of fat loss in most adults — sustainable, supported by appetite, and unlikely to trigger metabolic adaptation. Going larger (≥1,000 kcal/day deficit) accelerates loss but increases muscle loss, hunger, and the chance you abandon the plan within a few weeks.
How do I find my maximum heart rate?
The classic formula is 220 − your age (so a 35-year-old has an estimated max of 185 bpm). The Tanaka formula (208 − 0.7 × age) is more accurate for older adults. Both are population averages — your true max can be 10–20 bpm above or below. The most precise measure is a graded exercise test under medical supervision.
How accurate is the 90-minute sleep cycle?
The 90-minute average is well-established in sleep research, but individual cycles range from 80 to 120 minutes. Cycles also lengthen later in the night — the first cycle averages 70–100 minutes, the last 90–120. Use the calculator's recommendations as a starting point, then adjust ±10 minutes based on how alert you feel waking up.
How much protein per kilogram do I need?
The official RDA is 0.8 g/kg/day for sedentary adults. Practical optimums: light activity 1.0–1.2 g/kg, moderate strength training 1.6–2.0 g/kg, intense strength training or cutting 2.2 g/kg, endurance 1.2–1.6 g/kg, older adults 1.0–1.2 g/kg to prevent sarcopenia. Beyond ~2.2 g/kg there is little additional benefit.
Are the formulas behind these calculators free?
Yes — every formula we use is published in peer-reviewed literature, NIH guidelines, or ACSM textbooks. Each calculator's page links to the primary source, and the math is visible in your browser if you inspect the JavaScript.
Are my entries saved or sent anywhere?
No. Every UtilDaily health calculator runs entirely in your browser. Your weight, height, age, and other inputs never reach a server. You can verify this in DevTools' Network tab while using any tool.
References
- 1.Calculate Your Body Mass Index — NIH National Heart, Lung, and Blood Institute
- 2.ACSM's Guidelines for Exercise Testing and Prescription — American College of Sports Medicine
- 3.Target Heart Rates — American Heart Association
- 4.Dietary Guidelines for Americans 2020-2025 — USDA / HHS
- 5.Brain Basics: Understanding Sleep — NIH NINDS
- 6.Mifflin MD, St Jeor ST. A new predictive equation for resting energy expenditure. — Am J Clin Nutr 1990