Track your health metrics with our free calculators. BMI, body fat, calories, macros, water intake, pregnancy tools, and more.
Health numbers are personal, and they deserve better than one-size-fits-all guesses. This collection of free health and fitness calculators covers the measurements people actually track: body composition, daily calories and macros, hydration, training zones, and pregnancy milestones. Each calculator takes your inputs — height, weight, age, activity level, due date — and applies a published, named formula, so you always know which method produced the number. Everything runs instantly in your browser, free and without an account, and nothing you enter is stored or sent anywhere.
The directory is organized into three groups. Body composition holds the ten core tools: BMI, body fat, ideal weight, BMR, calories, macros, deficits, protein, and hydration. Fitness & training covers macro splits and heart-rate zones. Pregnancy & health collects the week-by-week, ovulation, due date, and weight-gain tools, plus BAC, A1c conversion, and two medical cost estimators.
The table below pairs every calculator in this directory with its key inputs and result, drawn from each tool's own description — no invented numbers, just what the tools actually do.
| Calculator | Key inputs | Output / method |
|---|---|---|
| BMI Calculator | Height and weight | Body Mass Index with category |
| Body Fat Calculator | Neck, waist (hips) circumferences, height | Body fat % via US Navy method |
| Ideal Weight | Height, frame | Healthy weight range |
| BMR Calculator | Age, sex, height, weight | Calories burned at rest |
| Calorie Calculator | BMR inputs + activity level, goal | Daily calorie needs |
| Macro Calculator | Calories, goal | Protein, carb, fat targets in grams |
| Calorie Deficit | Stats, goal weight, pace | Daily calorie target & timeline |
| Protein Intake | Body weight, goal | Daily protein target by weight & goal |
| Water Intake | Weight, activity | Daily water needs |
| Hydration by Weight | Body weight | Water target by body size |
| Macro Split | Calories, split percentages | Macro percentages converted to grams |
| Heart Rate Zones | Age, resting heart rate | Training zones via Karvonen formula |
| Pregnancy Week by Week | Due date or LMP | 40 weeks of sizes & symptoms |
| Ovulation Calculator | Cycle dates | Fertile window |
| Due Date Calculator | Last period or conception date | Estimated due date |
| Pregnancy Weight Gain | Pre-pregnancy BMI, current week | IOM gain ranges by BMI & week |
| Twins Weight Gain | BMI, week, twins | Twin-specific gain ranges by week |
| BAC Calculator | Drinks, weight, time, sex | Blood alcohol estimate |
| A1c Converter | HbA1c or average glucose | Converts A1c ↔ average glucose |
| Vasectomy Reversal Cost | Region, insurance | Cost bands & pregnancy odds |
| Invisalign Cost | Tier, insurance, FSA/HSA | Cost estimate tiers & payment options |
The composition group begins with the BMI Calculator, the standard screening index: weight in kilograms over height in meters squared, classified as underweight, normal, overweight, or obese. BMI is fast and population-tested, but it cannot tell muscle from fat — which is why the collection also includes the Body Fat Calculator, which uses the US Navy circumference method (neck and waist, plus hips for women) to estimate body fat percentage with nothing more than a tape measure. The Ideal Weight Calculator completes the picture with a healthy weight range for your height and frame.
Energy comes next. The BMR Calculator estimates the calories your body burns at complete rest — the baseline everything else builds on. The Calorie Calculator applies your activity level and goal (lose, maintain, gain) to that baseline to produce daily calorie needs. The Calorie Deficit Calculator goes one step further, pairing a daily target with the timeline it implies. Nutrition detail is handled by the Macro Calculator (protein, carbs, fat targets), the Protein Intake Calculator (daily target by body weight and goal), and the Macro Split Calculator (converting percentage splits into grams). The two hydration tools — Water Intake and Hydration by Weight — translate body size into a daily water target.
Training tools are few but precise. The Heart Rate Zone Calculator uses the Karvonen formula, which computes zones from heart rate reserve — your maximum heart rate minus your resting heart rate — rather than maximum heart rate alone. That personalization matters: two people of the same age with different resting rates get different fat-burning and cardio thresholds. If you train with a heart-rate monitor, this calculator turns its raw numbers into a plan.
The pregnancy group covers the full timeline. The Due Date Calculator estimates delivery from your last menstrual period or conception date; the Pregnancy Week by Week tool walks all 40 weeks with fetal sizes and symptoms; the Ovulation Calculator identifies the fertile window from cycle data for those trying to conceive. Weight management tools include the Pregnancy Weight Gain Calculator, which applies IOM ranges by pre-pregnancy BMI and week, and the Twins Weight Gain Calculator for twin-specific ranges.
General health is served by the BAC Calculator, which estimates blood alcohol from drinks, body weight, sex, and elapsed time — a planning tool, never a driving test. The A1c Converter translates between HbA1c and average glucose, the two ways diabetes numbers are reported. Two cost estimators — Vasectomy Reversal and Invisalign — round out the group with procedure cost bands, insurance, and FSA/HSA considerations.
Every calculator on this page names its method — BMI's index math, the Navy circumference formulas, Karvonen zones, IOM ranges, Naegele's rule — so the number you take away is one you can understand and defend. All computation happens locally in your browser: your weight, your cycle dates, your glucose log never leave your device. Pick the number you want to understand, enter what you know, and get an answer in seconds.