How is BMI calculated?
The BMI formula is:
BMI = Weight (kg) / Height² (m)
For example, if you weigh 70 kg and are 175 cm tall:
BMI = 70 / (1.75 × 1.75) = 22.9
This result falls in the normal weight category for adults.
BMI calculator – calculate your body mass index
Want to know whether your weight is in the normal range for your height?
Use Fitnaly's free BMI calculator to work out your body mass index and understand what the result means.
Quick, easy and with no sign-up.
Enter your height and weight to see your BMI.
BMI is an approximate indicator and is not a medical diagnosis.
What is BMI (body mass index)?
BMI (Body Mass Index) is an indicator that assesses the ratio between a person's weight and height.
It's used as a reference for weight status in adults – underweight, normal weight, overweight or obesity.
You don't need to do the math yourself – enter your height and weight in Fitnaly's BMI calculator and get your result instantly.
What does your BMI result mean?
Once you've calculated your body mass index, you can compare it with the standard BMI categories for adults.
| BMI | Category |
|---|---|
| below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25 – 29.9 | Overweight |
| 30 and above | Obesity |
Underweight
A BMI below 18.5 shows that weight is below the standard range for height. There can be different reasons, so it's important to look at the result together with other indicators.
Normal weight
A BMI from 18.5 to under 25 falls within the standard normal-weight range for adults.
It's a positive reference point, but it doesn't give the full picture of fitness, eating habits or health.
Overweight
A BMI from 25 to under 30 shows weight above the standard range for height.
The result can be a starting point for reviewing eating habits, physical activity and other individual factors.
Obesity
A BMI of 30 or above falls in the obesity category.
This result can be linked to increased health risk, but on its own it isn't enough for a diagnosis. We recommend discussing it with a health professional.
BMI is a useful reference, but it doesn't show the whole picture
Two people with the same height and weight can have the same BMI but different fitness levels and body composition.
Body mass index does not directly account for:
- The amount of muscle mass.
- Body fat percentage.
- How fat is distributed in the body.
- Individual characteristics and health status.
For example, an active athlete with more muscle mass can have a high BMI without it necessarily meaning excess body fat.
The standard adult BMI categories aren't suitable for directly interpreting results for children and teenagers. Pregnancy also calls for different assessment methods.
Use BMI as a starting point, not as the only indicator of your health.
Calculate your BMI. Take the next step with Fitnaly.
Your BMI result can help you understand the ratio between your weight and height. But to plan your meals, you also need to know your daily calorie needs.
With Fitnaly you can move from a one-time calculation to convenient tracking of your meals and activity.
Work out your calorie needs
Enter your weight, height, age, physical activity and goal. Fitnaly uses your personal details to estimate your daily calorie needs.
Choose a diet plan for your goal
Whether you want to lose weight, maintain your weight or gain muscle, you can start with a free meal plan.
With Fitnaly Pro you get a personal diet plan created with AI around your details and food preferences.
Track your calories and activity
Use Fitnaly's calorie and fitness tracker to log meals, macronutrients, water, steps and exercise.
Follow your calorie balance and weekly progress to make more informed decisions every day.
BMI is starting information. Your habits are what you can work on every day.
You know your BMI. But do you know how many calories you need?
BMI shows the ratio between weight and height, but it doesn't tell you how many calories to eat each day.
For that, it helps to calculate your BMR (basal metabolic rate) – the approximate energy your body uses at rest.
Adding your daily activity and personal goals gives you a better reference for your daily calorie needs.
Frequently asked questions about BMI
What is BMI?
BMI stands for Body Mass Index. It uses weight and height to give an approximate weight-status category for adults.
What is a normal BMI?
For most adults, the standard normal-weight range is a BMI from 18.5 to under 25. The value should be considered together with other health indicators and individual characteristics.
How do I calculate my BMI?
Divide your weight in kilograms by the square of your height in meters. You can also use Fitnaly's free BMI calculator, which does the calculation automatically.
Is Fitnaly's BMI calculator free?
Yes. The BMI calculator is completely free and you can use it right on the website, with no sign-up or app download.
Does BMI show body fat percentage?
No. BMI doesn't directly measure body fat percentage or muscle mass. Two people with the same BMI can have different body compositions.
Is BMI suitable for athletes?
BMI can serve as a general reference, but for people with more muscle mass the result can be misleading. That's why it shouldn't be the only indicator of fitness.
Can I use BMI to set a calorie deficit?
Not directly. BMI doesn't show daily energy expenditure. Planning a calorie deficit requires other factors too, including basal metabolic rate and physical activity.
What's the difference between BMI and BMR?
BMI assesses the ratio between weight and height, while BMR shows the approximate energy your body needs at rest. The two serve different purposes.
Does Fitnaly calculate my BMI automatically?
Yes. When you enter the required personal details in the app, Fitnaly calculates your BMI automatically. It's part of the information used to work out your nutritional needs and create your diet plan.
From your first calculation to better habits
Now you know how to calculate your BMI. The next step is understanding what your body needs and building eating habits that fit your life.
With Fitnaly you can track your calories, meals and activity, use a free meal plan or choose a personal AI diet plan.
Start for free, with no time limit.
Fitnaly – nutrition, movement and progress in one place.