BMI tells you where you are. A calorie calculator tells you what to eat to get where you want to be. Here's how to use both together.
Before working out calories, you need a clear picture of where you stand. BMI (Body Mass Index) gives you a quick read on whether your current weight is in a healthy range for your height.
| BMI Range | Category | What it means for calories |
|---|---|---|
| Below 18.5 | Underweight | Calorie surplus needed — aim for slow weight gain |
| 18.5 – 24.9 | Normal weight | Maintenance calories — focus on body composition |
| 25.0 – 29.9 | Overweight | Moderate deficit — 300 to 500 kcal below TDEE |
| 30.0+ | Obese | Structured deficit — 500 to 750 kcal below TDEE |
For people of Asian descent, the overweight threshold starts at BMI 23 rather than 25. Check your number using our BMI Calculator or the Asian BMI Calculator if applicable.
TDEE stands for Total Daily Energy Expenditure — the number of calories your body burns in a day including all activity. This is your baseline. To lose weight you eat below it. To gain weight you eat above it. To maintain, you match it.
TDEE is calculated in two steps. First, your BMR (Basal Metabolic Rate) — the calories burned at rest — is estimated using the Mifflin-St Jeor formula:
BMR is then multiplied by an activity factor to get TDEE:
| Activity Level | Multiplier |
|---|---|
| Sedentary (desk job, little exercise) | × 1.2 |
| Lightly active (exercise 1–3 days/week) | × 1.375 |
| Moderately active (exercise 3–5 days/week) | × 1.55 |
| Very active (hard exercise 6–7 days/week) | × 1.725 |
Skip the manual calculation — use our Calorie Calculator to get your TDEE instantly.
Once you know your TDEE and your BMI, you can set a realistic calorie target. The relationship between calorie deficit and weight loss is well established: a deficit of approximately 7,700 calories produces 1 kg of fat loss.
| Goal | Calorie Target | Expected rate |
|---|---|---|
| Slow loss (safer for older adults) | TDEE − 300 kcal | ~0.3 kg/week |
| Standard loss | TDEE − 500 kcal | ~0.5 kg/week |
| Faster loss (BMI over 30) | TDEE − 750 kcal | ~0.75 kg/week |
| Maintenance | = TDEE | No change |
💡 Never go below 1,200 kcal/day for women or 1,500 kcal/day for men. Eating too little slows metabolism, causes muscle loss, and makes the deficit unsustainable.
Here's a full worked example to show how BMI and calorie calculation connect in practice.
| Detail | Value |
|---|---|
| Person | Female, 42 years old |
| Height | 163 cm (5'4") |
| Current weight | 78 kg |
| Current BMI | 29.3 (overweight) |
| Goal BMI | 23.0 (upper normal) |
| Goal weight | 61 kg |
| Weight to lose | 17 kg |
| BMR (Mifflin-St Jeor) | 1,512 kcal |
| TDEE (lightly active × 1.375) | 2,079 kcal |
| Target calories (−500 deficit) | 1,579 kcal/day |
| Expected timeline at 0.5 kg/week | ~34 weeks (8 months) |
A useful way to think about this: each BMI point corresponds to roughly 2.5 to 3 kg for most adults (depending on height). At a deficit of 500 kcal/day losing 0.5 kg/week, dropping one BMI point takes approximately 5 to 6 weeks.
For reference at common heights:
| Height | Weight per 1 BMI point | Time to drop 1 BMI point (at −500 kcal/day) |
|---|---|---|
| 155 cm | ~2.4 kg | ~5 weeks |
| 163 cm | ~2.7 kg | ~5–6 weeks |
| 170 cm | ~2.9 kg | ~6 weeks |
| 178 cm | ~3.2 kg | ~6–7 weeks |
If you are of Asian descent, your healthy BMI ceiling is 22.9 rather than 24.9. This means the calorie deficit needed to reach a healthy BMI is somewhat larger than the standard chart suggests. A person of Chinese, Malay, or Indian descent with a BMI of 26 is two full BMI points into the overweight range under Asian guidelines, not just one.
Use the Asian BMI Calculator to find your correct target weight first, then plug that into the calorie calculation.
Calories in versus calories out is the primary driver of weight change, but several other factors affect how quickly BMI responds.
⚠️ BMI and calorie calculators provide estimates based on population averages. Individual metabolism varies. If you have a medical condition affecting weight or metabolism, consult a doctor or registered dietitian before making significant dietary changes.
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