To estimate your daily calorie needs, use a two-step process. First, calculate your Basal Metabolic Rate (BMR) — the calories your body burns at rest — using the **Mifflin-St Jeor equation** (currently considered the most accurate for most people):
**BMR = (10 × weight in kg) + (6.
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To estimate your daily calorie needs, use a two-step process. First, calculate your Basal Metabolic Rate (BMR) — the calories your body burns at rest — using the **Mifflin-St Jeor equation** (currently considered the most accurate for most people):
**BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161**
Then multiply by your activity level to get your Total Daily Energy Expenditure (TDEE):
- Sedentary: × 1.2
- Lightly active (1–3 days/week): × 1.375
- Moderately active (3–5 days/week): × 1.55
- Very active (6–7 days/week): × 1.725
- Extremely active: × 1.9
**Quick example:** A 30-year-old woman, 5'5" (165 cm), 150 lbs (68 kg), lightly active → BMR ≈ 1,500 calories → TDEE ≈ **2,050 calories/day**.
Treat this as a *starting point*, not a precise prescription. Metabolism varies significantly between individuals due to genetics, muscle mass, hormones, and health conditions — estimates can be off by 200–400 calories. The most practical approach is to track your energy levels and weight over 2–3 weeks and adjust from there. Consult a registered dietitian or your doctor if you have thyroid issues, a metabolic condition, are pregnant, or have a history of disordered eating.
Where the AIs Agree
All responses agree that calculating calorie needs involves two core steps: estimating BMR and then multiplying by an activity factor to get TDEE.
All agree on the same activity multipliers (1.2 for sedentary through 1.9 for extremely active).
All responses emphasize that these formulas are estimates, not exact figures, and that individual variation is significant.
All agree that factors like muscle mass, hormones, genetics, and health conditions can meaningfully affect actual calorie needs.
All responses recommend consulting a healthcare professional when specific health concerns or conditions are present.
All agree that the goal of the calculation adjusts depending on whether you want to maintain, lose, or gain weight.
Where the AIs Disagree
**Which formula to use:** ChatGPT and Claude recommend the **Mifflin-St Jeor equation** as the most current and evidence-based option, while Grok defaults to the older **Harris-Benedict equation**, which is generally considered slightly less accurate for modern populations.
**Unit conventions:** Grok uses imperial units (pounds/inches), while ChatGPT and Claude use metric (kg/cm), which can cause confusion or conversion errors depending on the user's familiarity.
**Women-specific nuance:** Grok explicitly notes that the Harris-Benedict formula doesn't account for menstrual cycles or pregnancy — the other responses don't address this, which is a meaningful gap for women.
**Depth of practical guidance:** Claude adds a useful "reality check" suggesting weight/energy monitoring over 2–3 weeks as an alternative to pure calculation, which the others don't emphasize as strongly.
**Confidence framing:** Claude is the most explicit about the margin of error (200–400 calories), while the others treat the formula outputs with slightly more implied precision.