How many calories do you actually need?
Your daily calorie needs come from three things you can estimate in a minute. Here's how the maths works, where it goes wrong, and how to find your real number.
Every fat loss or muscle gain plan starts with the same question: how much should I eat? The honest answer is that nobody can tell you exactly from a formula. But a formula gets you close enough to start, and your own data does the rest.
Your daily burn has three parts
The energy you use each day, called total daily energy expenditure, is roughly made of:
- Resting burn (basal metabolic rate). What your body uses just to keep you alive: breathing, circulation, brain, organs. For most people this is 60 to 70 percent of the day’s total.
- Movement. Exercise, plus everything else you do on your feet: walking to the car, fidgeting, standing at work. This varies more than anything else between people.
- Digesting food. Breaking down what you eat costs around 10 percent of what you eat, a little more when your diet is high in protein.
Step 1: estimate your resting burn
The most widely used equation today is Mifflin St Jeor. A 2005 systematic review compared the common equations against measured resting burn and found Mifflin St Jeor was the most reliable, landing within 10 percent of the measured value for most healthy adults.
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
For a 30 year old man who weighs 80 kg and is 175 cm tall, that’s 800 + 1,094 − 150 + 5, or about 1,750 calories a day at rest.
Step 2: multiply by how active you are
| Your week | Multiply by |
|---|---|
| Mostly sitting, little exercise | 1.2 |
| Light: on your feet some, or 1 to 3 workouts | 1.375 |
| Moderate: 3 to 5 workouts | 1.55 |
| High: hard training 6 to 7 days | 1.725 |
| Athlete, or a physical job plus training | 1.9 |
Our example man trains four days a week, so 1,750 × 1.55 gives roughly 2,710 calories to maintain his weight.
Be honest here. Most people overestimate how active they are, especially if they train hard for an hour but sit for the other fifteen waking hours. If you’re unsure, pick the lower option.
Step 3: adjust for your goal
- To lose fat, eat less than your burn. A kilogram of body fat holds roughly 7,700 calories, so eating about 550 calories a day under maintenance works out to around 0.5 kg a week.
- To build muscle, eat a little more. A surplus of 200 to 300 calories a day is plenty for most people. More than that mostly adds fat.
- To maintain, eat at your burn and let your training do the work.
There are limits. We don’t suggest going below about 1,500 calories a day for men or 1,200 for women without professional supervision, and never below your resting burn. Faster isn’t better: see how fast should you lose weight.
Why the formula is only a starting point
Equations describe the average person. You are not the average person. Two people with identical stats can burn several hundred calories a day apart because of muscle mass, daily movement and genetics.
The 7,700 calorie rule also oversimplifies. Research modelling weight change shows that as you lose weight, you burn less, so progress naturally slows over months even when you eat the same. That’s not your metabolism breaking. It’s physics: a smaller body costs less to run.
How to find your real number
The best calorie calculator is your own data:
- Eat at your estimated target and log it honestly for two to three weeks.
- Weigh yourself most mornings, after the toilet and before food.
- Look at the trend, not single days. Daily weight jumps around for reasons that have nothing to do with fat.
- If your trend moves faster or slower than planned, adjust by 100 to 150 calories and repeat.
This is exactly how the Logpulse weekly check-in works. Once you have enough full days of food and enough weigh ins, it works out what your body actually burns from your intake and your weight trend, then suggests new targets for you to approve.
Want to see your starting numbers? Try the calorie and macro calculator.
This is general information drawn from published research, not personal medical or dietary advice. If you have a health condition, are pregnant, or have a history of disordered eating, speak to your GP or an Accredited Practising Dietitian first. For support with eating concerns, the Butterfly Foundation helpline is 1800 33 4673.
Sources
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition. 1990;51(2):241 to 247.
- Frankenfield D, Roth Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association. 2005;105(5):775 to 789.
- Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. The Lancet. 2011;378(9793):826 to 837.