Losing weight isn’t complicated, but it’s easy to get it wrong — undereating, losing muscle instead of fat, or chasing the scale while ignoring what your body actually looks like. This guide walks you through it in order: the numbers you need, the target you should set, how to protect your muscle while you cut, and how to actually track progress. Every step links straight to the calculator you need — no signup, no guesswork.
Meet Maya
Maya is 38, 160cm, and started this process at 80kg, working a desk job with light activity a few times a week. She’s used throughout our articles as a real-world example of midlife weight loss done sustainably — not through crash diets, but through knowing her actual numbers and adjusting gradually. You’ll see her numbers referenced as you go through the steps below, so you can see exactly how each calculation plays out for a real case rather than just an abstract formula.
Step 1: Know Your Numbers
Before you can set a calorie target, you need two baseline numbers, and they answer two different questions.
BMI is a quick screening ratio of weight to height. It takes seconds to calculate and is useful as a rough population-level indicator, but it has a real limitation worth understanding upfront: it can’t tell the difference between muscle and fat. A muscular person and an out-of-shape person at the same height and weight can show the identical BMI number despite having very different body compositions. Use it as a starting reference point, not a verdict.
TDEE (Total Daily Energy Expenditure) is the number that actually matters for weight loss — it’s the real number of calories your body burns in a full day, including your basal metabolism plus all your activity. Everything in Step 2 is built from this number, not from BMI.
Here’s how it plays out for Maya: using the Mifflin-St Jeor equation, her basal metabolic rate (BMR) comes out to roughly 1,485 calories — that’s what her body burns doing nothing at all. Factoring in her light activity level (a multiplier of ×1.375), her TDEE lands at approximately 2,042 calories. That 2,042 figure, not her BMR, is what her calorie target in Step 2 will be based on.
Want the full explanation behind these numbers, including the exact formulas used?
- What is a Healthy BMI for Men and Women
- What is BMR and How to Use It
- What is TDEE and How to Use It
- BMR vs TDEE: What’s the Difference
Step 2: Set Your Target
Once you know your TDEE, the actual math of fat loss is simple: eat consistently below it. The size of that gap — your deficit — is where most people get it wrong.
A deficit of 300–500 calories below TDEE is the range that reliably produces fat loss without the downsides of going too aggressive. Roughly, a 500-calorie daily deficit works out to about 0.45kg (1lb) of loss per week; a 300-calorie deficit is closer to 0.25–0.3kg per week. Slower feels less dramatic, but it’s far more likely to actually stick, and it protects against the muscle loss and metabolic slowdown that come with crash-dieting.
For Maya, that means a target somewhere between 1,542 and 1,742 calories a day — not the 1,485 her BMR alone might suggest. That difference matters: eating at BMR ignores the calories she’s already burning through daily activity, and consistently undereating relative to TDEE is one of the most common reasons people feel constantly fatigued, hit plateaus, or eventually give up.
Give any target at least 2–3 weeks before judging whether it’s working — weight fluctuates daily from water, sodium, and hormonal cycles, and short-term stalls are normal, not necessarily a sign the number is wrong.
Step 3: Protect Your Muscle While You Cut
Weight loss and fat loss aren’t the same thing. Cut calories without enough protein, and a meaningful share of what you lose can be muscle rather than fat — which quietly lowers your metabolism and leaves you looking softer at a lower weight, not leaner. Protein is what tells your body to hold onto muscle even while you’re in a deficit.
A practical target during a cut is roughly 1.6–2.2 grams of protein per kilogram of current bodyweight — noticeably higher than general population guidelines, precisely because you’re actively trying to preserve muscle under a calorie restriction. For Maya at 80kg, that works out to 128–176g of protein a day, spread across her meals rather than loaded into one sitting, since muscle protein synthesis responds better to protein intake distributed through the day.
Step 4: Track Body Composition, Not Just the Scale
The scale measures total mass — water, muscle, fat, even the contents of your last meal — all lumped into one number. It can stay flat for weeks while you’re genuinely losing fat, or jump overnight from sodium and water retention with zero relation to fat loss. This is why relying on the scale alone is one of the most common reasons people think a working plan “isn’t working.”
Body fat percentage tells you what’s actually changing underneath the total number. Two people at the same weight can look completely different depending on how much of that weight is muscle versus fat — this is exactly why Maya tracks her estimated body fat percentage alongside her weight, checked every 2–3 weeks rather than daily, using the same method and conditions each time (same time of day, same state of hydration) so the comparison is meaningful.
Common Mistakes to Avoid
- Eating at your BMR instead of your TDEE — this creates too large a deficit and often backfires through fatigue, muscle loss, and eventual bingeing.
- Ignoring protein — a deficit without enough protein costs you muscle, not just fat, and undermines the whole point of losing weight in the first place.
- Judging progress by the scale alone — water retention, glycogen shifts, and normal fluctuation can mask real fat loss for weeks at a time.
- Changing your target too often — give any calorie target at least 2–3 weeks before adjusting it; reacting to daily noise leads nowhere.
Related Reading
- How to Lose Belly Fat — What Actually Works
- Best Foods to Eat on a Calorie Deficit
- What is My Ideal Weight for My Height
Ready to Start?
The first step is knowing your number. Calculate your TDEE now, then follow the steps above in order.
Disclaimer: This guide is for informational and educational purposes only and does not constitute medical or nutritional advice. Individual results vary; always consult a qualified healthcare professional before starting a weight loss program.