Choose the calculator for your question
These five tools cover different inputs and outputs. Start with the result you need, then open the calculator whose required measurements or details you have available.
- Age Calculator uses a date of birth and today or another target date to calculate calendar age and date-based totals.
- BMI Calculator uses height and weight to calculate BMI and a standard weight category.
- Body Fat Percentage Calculator estimates body fat with the US Navy circumference method using height, neck, and waist measurements; Female mode also uses hip circumference.
- Calorie Calculator estimates BMR, maintenance calories (TDEE), and a goal-based daily target from height, weight, age, sex, activity level, and goal.
- Calories Burned Calculator estimates activity calories from body weight, activity or a custom MET value, duration, and optional distance where supported.
BMI and body-fat estimates answer different questions
BMI is a height-and-weight screening ratio. It supports metric and imperial input and returns a standard weight category, but it does not account for muscle mass, bone density, body-fat distribution, age, sex, or ethnicity. Use the BMI Calculator when height and weight are the measurements you want to compare.
The Body Fat Percentage Calculator uses separate Male and Female US Navy circumference formulas and accepts metric or imperial measurements. It requires height, neck circumference, and waist circumference; Female mode also adds hip circumference. BMI and body-fat percentage are not interchangeable, and neither output is a diagnosis.
Daily calorie needs versus calories from an activity
Use the Calorie Calculator for a daily estimate. It uses the Mifflin-St Jeor formula for BMR, applies a selected activity multiplier for TDEE, and applies a fixed -500, 0, or +500 kcal/day adjustment for a losing, maintaining, or gaining goal. It accepts metric or imperial height and weight, age 15 through 120, sex, five activity levels, and three goals.
Use the Calories Burned Calculator for one activity or session. It uses Calories = MET x weight (kg) x duration (hours). You can choose an activity or enter a custom MET value; walking, running/jogging, and cycling can use distance to derive pace, while other activities use fixed activity-specific MET values. The result includes an estimate and range because MET values are population averages.
A practical way to use the health calculators
- Start with the output needed: a date calculation, height-and-weight ratio, circumference-based estimate, daily calorie estimate, or activity estimate.
- Choose metric or imperial input where the selected calculator provides that control.
- Enter the required values and review the displayed formula, assumptions, intermediate values, and result.
- For calorie and body-composition results, treat the output as an estimate and read the tool-specific limitations before using it for a decision.
For date-specific rules, review the Age Calculator inputs and date rules. For the daily estimate, review the Calorie Calculator formula and assumptions.
Interpret results within their stated limits
The Age Calculator performs date arithmetic and does not apply a jurisdiction's legal, medical, or eligibility rules. BMI is a screening ratio rather than a diagnosis. The body-fat tool produces a deterministic estimate from entered measurements and notes that a full evaluation may require professional assessment.
Actual energy needs and expenditure vary with factors such as metabolism, body composition, fitness, technique, and conditions. The calorie tools show their formulas or assumptions so you can inspect how each result was produced. Read the BMI limitations, body-fat estimate limitations, and calorie-estimate limitations before treating a result as more than an estimate.