Understanding your maintenance calories and a reasonable daily target is a useful starting point for anyone curious about how energy balance works — not a prescription for what to eat. Use our free Calorie Deficit Calculator to estimate BMR and TDEE using the Mifflin-St Jeor formula.
BMR — Basal Metabolic Rate
Basal Metabolic Rate (BMR) is the number of calories your body needs at complete rest just to keep essential functions running — breathing, circulation, cell repair. It's the baseline before any walking, exercise, or daily activity is accounted for.
TDEE — Total Daily Energy Expenditure
Total Daily Energy Expenditure (TDEE) is BMR adjusted for your activity level. It represents your estimated maintenance calories — the amount you'd need to consume daily to maintain your current weight, given how active you are. TDEE is what most people mean when they talk about "maintenance calories."
The Mifflin-St Jeor Formula
The Mifflin-St Jeor equation is generally considered one of the more accurate BMR estimation formulas for most adults, though any formula produces an estimate — not an exact measurement. Individual metabolism varies based on body composition, genetics, health conditions, and other factors no single equation can capture fully.
What a Calorie Deficit Means
A calorie deficit means consistently eating below your TDEE so the body draws on stored energy (primarily fat) over time. Moderate, sustainable deficits — commonly cited general guidance is around 500 calories per day below maintenance, roughly translating to about 0.5 kg or 1 lb of fat loss per week — tend to be easier to sustain and more likely to preserve muscle mass and energy levels compared to very large or aggressive deficits.
Important Note — Not Medical Advice
This tool provides a general estimate for informational purposes only, not medical or nutritional advice. Anyone with health conditions, a history of disordered eating, who is pregnant or breastfeeding, or who is pursuing a significant deficit should consult a doctor or registered dietitian before making major dietary changes.
Related Health Tools
For another common body-metric reference point, see our BMI calculator guide and use the BMI Calculator.
Frequently Asked Questions
What's the difference between BMR and TDEE?
BMR is the calories your body needs at complete rest just to function. TDEE adds your activity level on top of BMR, representing your actual daily maintenance calories.
How big of a calorie deficit is safe?
A commonly cited general guideline is a moderate deficit of around 500 calories/day below maintenance, which tends to be more sustainable than very aggressive deficits. Significant or rapid deficits should be discussed with a doctor or registered dietitian, especially for extended periods.
Is the Mifflin-St Jeor formula 100% accurate for everyone?
No formula perfectly predicts individual metabolism — Mifflin-St Jeor is widely regarded as one of the more reliable general estimation formulas, but actual results vary by individual factors like body composition and health conditions.
Should I consult a doctor before starting a calorie deficit?
Yes, especially if you have any underlying health conditions, a history of disordered eating, are pregnant or breastfeeding, or are considering a significant or long-term deficit — a doctor or registered dietitian can give guidance specific to your situation.