How many calories a day to lose weight? Get the math right — and don't wreck your metabolism

Bilberry Guide · updated: 22 Jul 2026 · approx. 9 min read

The short answer: your total daily energy expenditure (TDEE), minus 300–600 kcal. All the difficulty sits in two places: you have to know your TDEE for real (not from a calculator), and you must not overdo the deficit. Below is the full calculation, step by step — with numbers.

Step 1: estimate your starting point

To start, the classic Mifflin-St Jeor formula for basal metabolic rate (BMR) is enough:

Men: BMR = 10×weight[kg] + 6.25×height[cm] − 5×age + 5
Women: BMR = 10×weight[kg] + 6.25×height[cm] − 5×age − 161

Multiply the result by an activity factor (PAL):

Example: a man, 90 kg, 180 cm, 40 years old, moderately active → BMR = 900 + 1125 − 200 + 5 = 1830 kcal; TDEE ≈ 1830 × 1.55 ≈ 2,840 kcal.

Step 2: match the deficit to yourself, not the calendar

A healthy, sustainable pace is losing 0.5–1% of body weight per week. A kilogram of body fat holds roughly 7,700 kcal of energy, so:

For our example, the moderate option gives a target of about 2,840 − 740 ≈ 2,100 kcal a day. The less you have to lose, the slower the pace you should pick — with the last few kilos, 0.25–0.5% a week is good sense, not weakness.

Why "the bigger the deficit, the better" is a trap

A very aggressive calorie cut looks tempting in a spreadsheet, but in practice it sabotages itself through four mechanisms at once:

You lose muscle, not just fat. With a large deficit and no strength training, as much as 30–40% of the weight lost can be lean tissue. The result: a lower TDEE after the diet and a "skinny fat" physique.

NEAT drops silently. Your body defends itself against a big deficit by cutting spontaneous movement — you walk less, sit more, and none of it is conscious. The real deficit ends up far smaller than the paper one.

Hunger beats willpower. Appetite is hormones (ghrelin, leptin), not character. A 1,000+ kcal deficit usually ends in a week of "making up for it" that wipes out all the progress — statistically, this is exactly where yo-yo dieting comes from.

Metabolic adaptation accelerates. The harsher the cut, the faster your body lowers its energy expenditure. After a "1,200 kcal" diet you come back to normal eating with your metabolism idling.

Step 3: protect your muscle — protein and strength

Two things make sure the weight you lose is fat, not muscle:

Protein: 1.6–2.2 g per kg of body weight daily. If you're overweight, calculate from your target weight, not your current one. Protein is also the most satiating macronutrient and has the highest cost of digestion (TEF) — in a deficit it works three jobs at once.

Resistance training 2–3 times a week. It doesn't have to be a gym — progressive bodyweight or resistance-band exercises are enough. The signal "these muscles are in use" is the only reason your body would spare them when energy is scarce.

Step 4: after 2–3 weeks, recalculate your target from real data

From the moment you have 2–3 weeks of food logs and daily weigh-ins, the formula stops being needed: you compute your actual TDEE from your own data (intake + change in the weight trend) and set the target against that. That's the heart of the adaptive TDEE method — and the reason two people "on the same diet" should be eating completely different calorie numbers a month in.

When the scale stalls for 3+ weeks (a plateau), check in this order:

1. Is the log still honest? (weekends, cooking oils, "uncounted" nibbling) — photo logging removes most of that friction.
2. Recompute your TDEE from the last 3 weeks — it has probably dropped (a lighter body + adaptation); lower the target by 100–200 kcal or add movement (NEAT).
3. If you've been in a deficit for many months — consider 1–2 weeks of eating at maintenance (a diet break); it doesn't undo your progress, and it resets your head and part of the adaptation.

How to measure progress without losing your mind

Day-to-day weight jumps by 1–2 kg from water alone, and that's normal. Look only at the weekly trend (a moving average), and alongside it: circumferences (waist, hips), physique photos every 2–4 weeks, strength in training, and how your clothes fit. Four indicators together don't lie — a single weigh-in lies notoriously.

Frequently asked questions

Is 1,200 kcal a good idea? Almost never without professional supervision. For most adults it's a deficit much steeper than 1% of body weight per week — with the whole package of consequences from the section on the big-deficit trap.

How much will I realistically lose in a month? In the first month, often 2–4 kg (including 1–2 kg of water and glycogen — which is why the start feels "fast"). After that, a realistic pace is 1–3 kg a month, depending on starting weight and deficit.

Count calories or macros? Calories decide how fast you lose; what you lose (fat vs muscle) is decided mainly by protein and training. The practical minimum: watch calories and protein, the rest is detail.

Does intermittent fasting (IF) speed up weight loss? Not by itself — it works when it helps you naturally eat less. If an eating window makes the deficit easier to hold, use it; if it ends in evening binges, it's not the tool for you.