If you’ve ever Googled “how many calories should I eat” and come away more confused than when you started, you’re not alone. The internet is awash with calorie calculators, all spitting out different numbers, and most of them are dangerously oversimplified. Worse, many of them will tell you to eat far less than your body actually needs.

Understanding your BMR and TDEE isn’t about obsessing over numbers. It’s about giving you a framework - a rough understanding of what your body requires - so that you can stop guessing, stop undereating, and start making informed decisions about how you fuel yourself.

I teach this to every woman I work with, not because I want them counting calories forever, but because knowledge removes fear. When you understand what’s happening inside your body, you stop falling for nonsense, and you start trusting yourself.

What is BMR? Your body’s baseline

BMR stands for Basal Metabolic Rate. It’s the amount of energy - measured in calories - that your body needs just to stay alive. Not to exercise. Not to walk around. Not even to digest food. Just to keep your heart beating, your lungs breathing, your brain functioning, and your cells repairing. The bare minimum for survival.

Think of it like the electricity bill for a house when nobody’s home - the fridge is running, the heating’s ticking over, the security light’s on. Even when you’re doing absolutely nothing, your body is using energy to maintain itself.

For most women, BMR falls somewhere between 1,200 and 1,600 calories per day, depending on age, height, weight, and body composition. Muscle burns more energy at rest than fat, so someone with more lean muscle mass will generally have a higher BMR.

Here’s the critical point: your BMR is the absolute floor of what you should be eating. It’s the minimum your body needs to function. Eating below this consistently tells your body that there isn’t enough fuel to survive - and it responds by slowing everything down, conserving energy, and holding onto fat stores.

What is TDEE? Your total daily energy use

TDEE stands for Total Daily Energy Expenditure. It’s your BMR plus everything else you do in a day - walking, working, cooking, cleaning, exercising, fidgeting, thinking, playing with the kids. It’s the total amount of energy your body actually uses across a full 24 hours.

Your TDEE is made up of several components:

  • BMR (60-70% of your total energy use) - The big one. Most of your energy goes on keeping you alive, not on exercise.
  • NEAT - Non-Exercise Activity Thermogenesis (15-30%) - All the movement that isn’t formal exercise: walking, carrying shopping, taking the stairs, gesturing while you talk, pacing around while on the phone. This varies hugely between people and is one of the biggest factors in individual metabolism.
  • TEF - Thermic Effect of Food (roughly 10%) - The energy your body uses to digest and process food. Protein requires the most energy to digest, which is one reason it’s so helpful for body composition.
  • EAT - Exercise Activity Thermogenesis (5-10%) - Formal exercise. Surprisingly, this is the smallest component for most people. A one-hour gym session might burn 200-400 calories, but your body uses 1,200-1,600 just to keep you alive.

For a moderately active woman, TDEE is typically somewhere between 1,800 and 2,400 calories per day. This is the total amount of energy her body is actually using.

Why most online calculators are misleading

Here’s where it gets problematic. Most calorie calculators you’ll find online use basic formulas that estimate your BMR based on age, height, and weight, then apply a rough multiplier for activity level. The result is a single number that’s supposed to tell you exactly what to eat.

The problem? These calculators can’t account for:

  • Your body composition. Two women who weigh the same but have different amounts of muscle will have very different metabolic rates. The calculators don’t know this.
  • Your dieting history. Years of restrictive dieting can suppress your metabolic rate significantly. A calculator doesn’t know if your metabolism has adapted to chronic undereating.
  • Your hormonal status. Perimenopause, thyroid function, stress levels - all of these affect your metabolism. A calculator doesn’t ask about any of them.
  • Your NEAT. Some people naturally fidget, pace, and move more throughout the day. Others are more still. This can account for hundreds of calories of difference. The “sedentary/moderate/active” dropdown can’t capture this.
  • Your individual biology. Genetics, gut health, sleep quality, medication - all of these influence how your body processes energy. A formula can’t factor in your unique physiology.

The numbers these calculators produce are rough estimates at best. At worst, they encourage people - particularly women - to eat far too little. I’ve seen countless calculators recommend 1,200 calories as a “weight loss” target. For most women, 1,200 calories is at or below their BMR. That’s not a weight loss plan. That’s a starvation plan.

Eating below your BMR doesn’t make you lose weight faster. It tells your body to hold on tighter.

The danger of eating below your BMR

I’ve written in detail about why restrictive diets fail, but it bears repeating here because this is where the real damage happens.

When you consistently eat below your BMR, your body enters a state of metabolic protection. It’s not burning fat efficiently - it’s trying to survive on inadequate fuel. Here’s what happens:

  • Your metabolism slows down. Your body becomes more energy-efficient, burning fewer calories for the same activities. This is metabolic adaptation - and it’s reversible, but it takes time and patience.
  • You lose muscle. When fuel is scarce, your body breaks down muscle tissue for energy. Muscle is metabolically expensive to maintain, so your body sacrifices it to conserve resources. Less muscle means an even lower metabolic rate.
  • Hunger hormones surge. Ghrelin (the hunger hormone) increases dramatically. Leptin (the satiety hormone) drops. Cravings become intense - not because you’re weak, but because your body is desperately trying to get you to eat.
  • Energy crashes. Without adequate fuel, you feel exhausted. Brain fog, irritability, poor concentration, disrupted sleep - your body is rationing energy and non-essential functions suffer.
  • Fat storage increases. When you do eat, your body is primed to store as much as possible as fat, in case the next “famine” hits. This is why the weight comes back so quickly after a crash diet - and why it often comes back as fat rather than muscle.

This isn’t a one-off response. Years of yo-yo dieting can leave your metabolism significantly suppressed. The good news is that it can recover - but it requires eating adequately and consistently, often for longer than people expect.

How to use this knowledge without obsessing over numbers

I want to be clear: I’m not suggesting you count every calorie for the rest of your life. That’s exhausting, and for many people it can trigger or worsen an unhealthy relationship with food. The point of understanding BMR and TDEE isn’t to create another set of rigid rules. It’s to give you context.

Here’s how I suggest using this information:

  1. Get a rough sense of your numbers. Use an online calculator as a starting point - not gospel truth. Know your approximate BMR so you have a floor you won’t go below. Know your approximate TDEE so you understand your body’s actual needs.
  2. Use it as a reality check. If a diet tells you to eat 1,200 calories, you now know that’s likely at or below your BMR. Red flag. If you’re eating 1,400 calories and exhausted, you now understand why - you’re probably underfuelling.
  3. Focus on food quality, not just quantity. Hitting your calorie needs with nutrient-dense whole foods feels completely different to hitting them with processed food. Protein, healthy fats, complex carbohydrates, plenty of vegetables - these fuel your body properly and keep you satisfied.
  4. Track for awareness, not control. If you do track your intake for a period, do it to learn - to understand portion sizes, to spot gaps in your nutrition, to see patterns. Then put the tracker away and use what you’ve learned intuitively.
  5. Listen to your body. Hunger is not the enemy. It’s information. If you’re hungry, eat. If you’re tired, rest. Your body is constantly communicating its needs - the more you listen, the less you need external rules.

What this means for sustainable fat loss

If your goal is to lose body fat in a way that actually lasts, here’s the framework:

Eat above your BMR, slightly below your TDEE. This creates a modest energy deficit - enough for your body to gradually use fat stores for fuel, but not so severe that it triggers the metabolic protection response. A deficit of roughly 200-500 calories below your TDEE is typically sustainable and effective.

That might mean eating 1,600-2,000 calories a day rather than the 1,200 that a magazine told you. It might mean eating more than you have been. And it might feel counterintuitive at first - especially if you’ve been told for years that less is more.

But here’s what happens when you fuel yourself properly:

  • Your energy comes back
  • Your workouts improve
  • Your sleep improves
  • Your cravings reduce
  • Your body starts to trust that food is available and gradually releases stored fat
  • You can sustain this approach long-term, because you’re not miserable

This is the approach we take in F.L.A.M.E. Not starving. Not obsessing. Understanding your body, fuelling it properly, and letting the changes happen at a pace that sticks.

The goal isn’t to eat as little as possible. It’s to eat as well as possible - and let your body do what it’s designed to do.

If you’ve spent years undereating and wondering why nothing works, I hope this has given you some clarity. You don’t need another 1,200-calorie meal plan. You need to understand your body - and then trust it.

If you’d like help working out what your body actually needs and building an approach that fits your life, that’s exactly what we do together in F.L.A.M.E. No calorie counting. No food rules. Just knowledge, support, and a plan that works with your body.