Free tool
Calorie calculator
Your maintenance calories are the kcal a day that keep your weight the same. Get a starting guess in 2 minutes. Then find your real number with a 4-week test.
kcal is the same as the "calories" on a food label. This tool goes with Part 3 of the Build Your Own Diet guide.
Your numbers stay on your phone. We never see them.
Before you start
This tool is for healthy people, 15 to 50 years old. It is not for you if you are pregnant or breastfeeding. It is not for you if you have a health condition such as diabetes, or kidney, liver, heart or gut disease. It is not for you if you have, or ever had, an eating disorder.
If any of this is you, please speak to a doctor or a registered dietitian first.
This tool is education. It is not medical advice. Read the medical disclaimer.
Please read
Your starting guess
0
kcal a day
Low end0
High end0
This range runs from the level below yours to the level above yours.
Every calorie calculator is a guess. Many people sit between 2 activity levels, and the equation is within 10% for only about 8 in 10 people. Kinda wild, right? So use this number to start. Then do the 4-week test to find the truth.
The equation was built from adults. For ages 15 to 18, treat this number as a rough start. Please speak to a doctor or a registered dietitian before you change how you eat.
The Guide is written for ages 19 to 50. If you have a health condition, ask your doctor first.
The 4 levels
Not sure about your level? Look at the levels next to yours.
| Level | kcal a day |
|---|---|
| InactiveYour pick | 0 |
| Low activeYour pick | 0 |
| ActiveYour pick | 0 |
| Very activeYour pick | 0 |
Now do the 4-week test.
It gives you your true number.
This is education. It is not medical advice. Medical disclaimer.
Your maintenance
about0
kcal a day
Calculator guess0 kcal
Your test0 kcal
The working
Here is how your numbers went in.
People often eat more than they log, and food labels can be wrong. Neither breaks the test. Logging the same way every day matters more than logging perfectly.
Now you know your number.
Go to Part 4 of the Guide and set your protein.
This is education. It is not medical advice. Medical disclaimer.
Remember my numbers on this device
Off by default. Saved only on this device. Never sent anywhere.
Under the hood
How it works
The equation, the error and the test maths
The equation
The page works out your resting calories with the Mifflin-St Jeor equation. Resting calories are what your body burns at rest. Use weight in kg, height in cm and age in years. The page changes feet, inches and pounds for you.
Men
Resting = (10 × weight) + (6.25 × height) − (5 × age) + 5
Women
Resting = (10 × weight) + (6.25 × height) − (5 × age) − 161
Then add your activity
Multiply your resting calories by the number for your level. That gives your calories a day.
- Inactive
- × 1.2
- Low active
- × 1.375
- Active
- × 1.55
- Very active
- × 1.725
Sources: the 1990 paper that made the equationand a 2005 review that compared several equations. The 4 activity numbers are the standard ones that most calorie calculators use.
How good is the guess?
In the 2005 review, this equation came within 10% of measured resting calories for about 8 in 10 healthy adults. That was better than the other equations. It still misses for about 2 in 10. The activity numbers add more error, because they are rough averages.
The range under your number runs from the level below yours to the level above yours. Many people sit between 2 levels. The equation was built from adults, so for ages 15 to 18 treat the number as a rough start.
The 4-week test
At the end of the test, the page works out this:
Maintenance = average daily intake
− (weight change in kg × energy per kg ÷ days)Weight change is the end trend weight minus the start trend weight. If weight went up, the number is positive. If it went down, the number is negative.
Energy per kg
- 2 to 4 weeks
- 5,000 to 6,000 kcal
- Over 6 weeks
- 6,000 to 7,000 kcal
This page uses the middle of the range. That is 5,500 kcal per kg for tests up to 42 days. It is 6,500 for longer tests. You can change it inside the allowed range.
Do not use the old "3,500 calories per pound" rule for a short test. It works out to about 7,700 kcal per kg. That is too high for the first few weeks. Early weight change is mostly water and glycogen (the carbs stored in your muscles and liver). They carry much less energy. If you use 7,700, your answer goes the wrong way.
Questions
Calorie calculator FAQ
What are maintenance calories?
Maintenance calories are the kcal a day that keep your body weight the same. Some sites call this TDEE, short for total daily energy expenditure. Eat less than your maintenance and you lose weight over time. Eat more and you gain.
How accurate is a calorie calculator?
Every calorie calculator is a guess. This one finds your resting calories with the Mifflin-St Jeor equation, then adds your activity level. In a large review, that equation came within 10% of measured resting calories for about 8 in 10 healthy adults. The activity step is rougher. That is why this page also has the 4-week test.
Why do I need a 4-week test?
Your daily weight is noisy. Water, salt and food in your gut move the scale more than fat does. You need about 28 days of weights to narrow the answer down. Even then it can be off by about 350 kcal a day. After 1 week it is close to useless.
How many calories should I eat to lose or gain weight?
Start from your maintenance number. Eating below it makes you lose weight. Eating above it makes you gain. This page does not give goal calories yet. Find your true maintenance first, because every goal number builds on it.
Do you keep the numbers I type?
No. The maths runs on your phone or computer. Nothing is sent to a server, and there is no account. The switch called Remember my numbers saves them on your own device only. It is off until you turn it on.
Last updated: 14 October 2026.
Want the why behind the numbers?
Get the articles by email
Short, plain posts on training and food. No spam.
Opens Substack to confirm. No spam, unsubscribe any time.