Calorie Calculator

How the Calorie Calculator Works

This calorie calculator uses the Mifflin-St Jeor equation — the most validated formula for estimating daily calorie needs. Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5. Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161. BMR is multiplied by an activity factor to get TDEE (Total Daily Energy Expenditure) — the actual calories you need each day.

Example: A 30-year-old woman, 140 lbs (63.5 kg), 5'5" (165.1 cm), moderately active. BMR = 10(63.5) + 6.25(165.1) − 5(30) − 161 = 635 + 1,031.9 − 150 − 161 = 1,355.9. TDEE = 1,355.9 × 1.55 = 2,102 calories/day to maintain weight.

Daily Calorie Needs by Activity Level

Your TDEE (Total Daily Energy Expenditure) = BMR × activity multiplier:

• Sedentary (×1.2): Desk job, no exercise. A 35-year-old woman 5'5" at 150 lbs: TDEE ~ 1,710 cal/day
• Lightly active (×1.375): Light exercise 1–3 days/week. Same person: TDEE ~ 1,959 cal/day
• Moderately active (×1.55): Exercise 3–5 days/week. TDEE ~ 2,209 cal/day
• Very active (×1.725): Hard exercise 6–7 days/week. TDEE ~ 2,458 cal/day
• Extra active (×1.9): Athlete + physical job. TDEE ~ 2,708 cal/day

The difference between sedentary and very active is nearly 750 calories per day for the same person. Most people overestimate their activity level — if you have a desk job and gym 3x/week, you're "lightly active," not moderately active.

How Many Calories Per Day to Lose Weight?

The foundational rule: a 500-calorie daily deficit ~ 1 lb of fat loss per week (1 lb fat = 3,500 calories). This is an approximation — actual results are slightly lower because the body adapts. Safe deficit ranges:

• 250–500 cal/day: 0.5–1 lb/week loss — gradual, sustainable, minimal muscle loss
• 500–750 cal/day: 1–1.5 lbs/week — moderate, works for most people
• 750–1,000 cal/day: maximum recommended without medical supervision

Women: never go below 1,200 cal/day. Men: 1,500 cal/day minimum. Below these levels, muscle loss accelerates and metabolism adapts downward significantly. Real example: A 40-year-old moderately active man, 5'11" at 200 lbs, TDEE ~ 3,100 cal/day. A 500-cal deficit = 2,600 cal/day targets ~1 lb/week loss.

Calories Per Day to Gain Muscle

A 250–500 cal/day surplus above TDEE, combined with resistance training, supports muscle growth. For lean bulking, 300 cal/day above TDEE is a good starting point — enough to fuel muscle synthesis without excessive fat gain. Higher surpluses (500–750 cal/day) are "dirty bulking" and produce more fat alongside muscle.

Natural muscle gain limits: 1–2 lbs per month for experienced lifters; 2–4 lbs/month for beginners. Protein is critical: target 0.7–1.0g per pound of bodyweight (1.6–2.2g/kg). For a 175 lb person: 123–175g protein daily. Total caloric needs during a bulk: TDEE + 10–15%.

Calorie Needs by Age

Metabolic rate declines roughly 2–3% per decade after age 20, primarily from muscle loss. USDA Dietary Guidelines 2020–2025 daily calorie recommendations for moderately active adults:

• Ages 19–30: Men 2,600–2,800 cal; Women 2,000–2,200 cal
• Ages 31–50: Men 2,400–2,600 cal; Women 1,800–2,000 cal
• Ages 51+: Men 2,200–2,400 cal; Women 1,600–1,800 cal

This explains why many people gain weight eating the same diet they ate in their 20s — their TDEE has declined as muscle mass decreased with age.

Why Calorie Calculations Are Estimates

The Mifflin-St Jeor equation is accurate within ±10% for 82% of people — better than any competing formula, but still an approximation. Individual metabolic rate varies by up to 15% due to genetics, thyroid function, gut microbiome, and other factors. The most accurate approach: use the calculator to set a starting point, track actual intake and weight for 2–3 weeks, then adjust. If weight is stable at 2,200 calories, that's your true TDEE — adjust from there.

Frequently Asked Questions

What is the minimum safe calorie intake?

Medical guidelines: 1,200 cal/day minimum for women, 1,500 cal/day for men, without medical supervision. Very low calorie diets (under 800 cal/day) should only be done under medical supervision with structured meal replacement protocols. Below minimum thresholds, meeting micronutrient needs becomes nearly impossible and metabolic adaptation becomes severe.

What is the difference between BMR and TDEE?

BMR (Basal Metabolic Rate) is calories burned at complete rest — just to maintain organ function, breathing, and circulation. TDEE (Total Daily Energy Expenditure) includes BMR plus all activity: exercise, walking, digesting food (thermic effect ~ 10% of calories consumed), and NEAT (non-exercise activity thermogenesis — standing, fidgeting, etc.). TDEE is the number you actually need to eat at to maintain weight.

How many calories should I eat to lose 2 pounds a week?

A 2-lb/week loss requires a 1,000 calorie/day deficit (1,000 × 7 = 7,000 cal ~ 2 lbs). This aggressive pace is generally only appropriate for people with TDEE above 3,000 calories (since they'd still eat 2,000+). For most people, 1–1.5 lbs/week is more sustainable and produces less muscle loss. Rapid weight loss (2+ lbs/week) significantly increases the risk of muscle loss, gallstones, and nutrient deficiencies.

Does eating late at night cause weight gain?

Meal timing has a much smaller effect than total caloric intake. You gain weight by eating more than you burn — when you eat is secondary. Late eating often correlates with overeating high-calorie snack foods, which is the real issue. Circadian rhythm research does show that calories consumed late at night may be stored slightly less efficiently in some people, but the effect is small compared to total daily calorie balance.

How many calories are burned walking?

Walking burns approximately 80–100 calories per mile for a 150-lb person, or 300–400 calories per hour at 3 mph. A brisk 30-minute walk burns about 150 calories — useful, but not a substitute for dietary changes when losing weight. You'd need to walk 5+ miles to offset one typical fast food meal. Exercise is critical for health and body composition, but calorie restriction is more efficient for weight loss.