"Eat less, move more" is the most repeated — and least useful — weight-loss advice. How much less? How much more? The answer is one number: your calorie deficit. Let's make it concrete so you never have to starve yourself again.
What Is a Calorie Deficit
Calorie deficit = calories burned − calories eaten. Only when intake falls below expenditure does the body burn stored fat. Bigger deficits lose weight faster, but deficits over ~500-800 kcal/day cost you muscle, wreck your metabolism, and rebound hard — not recommended.
What You Burn Each Day (TDEE)
Total daily expenditure (TDEE) = basal metabolic rate (BMR) + activity + the thermic effect of food. BMR — the calories you'd burn at rest — is the biggest chunk and depends on age, sex, weight, and muscle mass.
Quick estimate (Mifflin-St Jeor): men BMR ≈ 10×kg + 6.25×cm − 5×age + 5; women −161. Multiply by an activity factor (sedentary 1.2 / light 1.375 / moderate 1.55 / very active 1.725) for TDEE.
No math by hand — enter height, weight, age in the calorie calculator and get your BMR and TDEE instantly.
The ~3,500-Calorie Rule
About 3,500 kcal of deficit ≈ 1 pound of fat (≈7,700 kcal per kg). This is the exchange rate of fat loss:
- A 500 kcal daily deficit → about 1 lb (0.45 kg) per week, ~4 lb a month
- A 300 kcal deficit → ~2.4 lb a month, gentler and more sustainable
Worked Example: Your Plan
Say your TDEE is 2,000 kcal and you want a 500 kcal daily deficit:
| Approach | How | Result |
|---|---|---|
| Only eating less | Eat 1,500 kcal/day | Hungry, hard to sustain, risks muscle loss |
| Eat + move | Eat 1,700 kcal + burn 300 via exercise | ✅ Sustainable, preserves muscle |
You can build the deficit from both sides — "7 parts diet, 3 parts exercise" is the everyday version of this math.
Check Your BMI First
Confirm you actually need to lose:
- BMI 18.5-24.9 (normal) → maintain; no aggressive cutting needed
- BMI 25-29.9 (overweight) → a gentle deficit is appropriate
- BMI 30+ (obese) → consult a professional and go gradually
Measure first with the BMI calculator — don't let "skinny anxiety" drive the plan.
Safety Notes
- Never eat below BMR: that triggers starvation mode and a slower metabolism
- Protect protein: aim for 1.2-1.6 g per kg of body weight to keep muscle
- Review weekly: log with the calorie calculator and adjust — if you lose too fast, ease off
Weight loss is a calorie-deficit math problem, but it's also a long game. Know your numbers, pick a pace you can hold for six months — that beats a crash diet every time.