Free fitness calculators

Which calculator do you need?

Each tool answers one common question. If you're not sure where to start, pick the one that matches what you're trying to do right now.

• "How much should I eat?" Start with the calorie calculator. It estimates your maintenance calories, the amount that keeps your weight about the same, and gives gentle targets if you want to lose or gain weight slowly.
• "Am I eating enough protein?" The protein calculator gives you a daily range based on your body weight and how you train, and splits it across your meals so it's easier to act on.
• "How strong am I, and what weight should I use?" The one-rep max calculator estimates the most you could lift once from a normal set, so you never have to test a true max. It also turns that number into weights for common training percentages.
• "How fast am I running, and what could I race?" The running pace calculator converts between pace, time and distance in kilometers or miles, and predicts race times from a recent result.
• "How hard should my cardio feel?" The heart rate zone calculator turns your age and resting heart rate into five training zones, from very easy to all-out.

Using them together

The calculators work best as a set, because fitness is mostly a few simple numbers that affect each other. A sensible order for most people:

1. Find your calories. Your energy intake decides whether your weight goes up, down or stays the same over time. Everything else builds on this.
2. Set your protein. Within those calories, enough protein helps you keep and build muscle, especially if you lift weights or are eating a little less than usual.
3. Plan your training. Use the one-rep max calculator to choose weights for strength work, and the pace and heart rate tools to keep most of your cardio easy and a small part of it hard.
4. Check in every few weeks. Your body changes as you train. Re-run the calculators every month or so, or whenever your weight, fitness or routine changes noticeably.

How accurate are the results?

Every calculator here uses an established, published formula: Mifflin-St Jeor for calories, Epley and Brzycki for one-rep max, Riegel for race predictions, and Tanaka and Karvonen for heart rate. These formulas are widely used by coaches, dietitians and researchers because they work well on average.

"On average" is the important part. Formulas describe large groups of people, and any one person can be noticeably above or below the result. Your genetics, muscle mass, sleep, stress, training history and even the weather can shift your real numbers. That's why each calculator page explains the math with a worked example, says plainly where the estimate can be off, and suggests how to adjust it using what you actually see, such as your weight trend over a few weeks or how an easy run really feels.

Treat every result as a well-informed starting point, not a verdict. If your body tells you something different from the calculator, your body wins.

Who these tools are for

The calculators are designed for healthy adults who want practical numbers for everyday training and eating. They are not designed for children and teenagers, during pregnancy, for people managing a medical condition, or for anyone with a history of disordered eating. In those situations, the safest numbers come from a doctor, registered dietitian or qualified coach who knows your situation.

Your privacy

The calculations run entirely in your browser. Nothing you type, including your age, weight or race times, is sent to the server or stored. You can use every calculator without an account, and close the page whenever you like.

Results are estimates for healthy adults, not medical advice. Read the health disclaimer.