Frequently Asked Questions

TDEE stands for Total Daily Energy Expenditure. It's the total number of calories your body burns in a 24-hour period, including:

• Basal Metabolic Rate (BMR): Calories burned at complete rest (breathing, circulation, cell production) — typically 60-75% of TDEE
• Exercise Activity Thermogenesis (EAT): Calories burned during intentional exercise — typically 5-30% of TDEE
• Non-Exercise Activity Thermogenesis (NEAT): Calories from fidgeting, walking, daily tasks — typically 15-30% of TDEE
• Thermic Effect of Food (TEF): Calories burned digesting food — typically 10% of TDEE

Understanding your TDEE is the foundation of any weight loss, maintenance, or muscle gain plan.

BMR (Basal Metabolic Rate) is the calories you burn at complete rest—just staying alive in bed all day.

TDEE is your BMR multiplied by your activity level, representing total daily calorie burn including all movement, exercise, and daily activities.

You should never eat below your BMR for extended periods, as your body needs these calories for essential functions. Weight loss targets should be based on your TDEE, not BMR.

Online calculators using validated formulas like Mifflin-St Jeor (which we use by default) are accurate within ±10% for approximately 98% of healthy adults.

However, individual metabolism varies due to:

• Genetics (some people are naturally "fast" or "slow" metabolizers)
• Muscle mass (muscle burns more calories than fat at rest)
• Hormonal factors (thyroid, cortisol, insulin sensitivity)
• Dieting history (metabolic adaptation from previous diets)
• Sleep quality and stress levels

See our Calculator Limitations page for full transparency on edge cases where accuracy may be reduced.

The Mifflin-St Jeor equation (1990) is considered the most accurate for approximately 98% of the general population, with a standard error of only ±10%.

A 2005 systematic review comparing all major formulas (Harris-Benedict, Mifflin-St Jeor, Owen, WHO/FAO/UNU, and others) found that Mifflin-St Jeor demonstrated the most accurate predictions across diverse populations.

Why it's more accurate than Harris-Benedict:

• Developed in 1990 (vs. Harris-Benedict from 1919/1984)
• Based on modern population data
• Accounts for changes in body composition and lifestyle since early 1900s
• Validated on larger, more diverse sample size (498 subjects)

See our Scientific References page for full citations and studies.

No need to be exact. Your TDEE is an estimate with natural day-to-day variance of ±100-200 calories due to sleep quality, stress, activity fluctuations, and digestion.

Aim for weekly averages rather than daily precision. If your TDEE is 2,000 calories:

• Eating 1,900-2,100 daily (averaging 2,000 per week) is perfectly fine
• Some days eating 1,800 and others 2,200 (still averaging 2,000) also works
• Being within ±10% of your target is good enough

Safe and sustainable calorie deficits:

• 250 calories below TDEE: Lose ~0.5 lb/week (slow but easy to maintain, minimal muscle loss)
• 500 calories below TDEE: Lose ~1 lb/week (recommended maximum for most people)
• 750 calories below TDEE: Lose ~1.5 lb/week (only for those with 50+ lbs to lose)
• 1000 calories below TDEE: Lose ~2 lb/week (only with medical supervision, risk of muscle loss)

Our TDEE Calculator automatically calculates safe deficit levels when you select your weight loss goal.

For lean muscle gain with minimal fat accumulation:

• Beginners (0-1 year training): +300-500 calories (can gain muscle faster, tolerate higher surplus)
• Intermediate (1-3 years training): +250-350 calories (slower gains, less fat with moderate surplus)
• Advanced (3+ years training): +200-300 calories (muscle gain is slowest, minimize fat gain)

Without training stimulus, eating above TDEE will just result in fat gain, not muscle gain.

Yes, but only in specific scenarios:

• You're a beginner to strength training ("newbie gains" allow simultaneous fat loss and muscle gain for 6-12 months)
• You're returning after a long break ("muscle memory" accelerates regain of lost muscle)
• You have high body fat (25%+ men, 32%+ women—enough energy stores to fuel muscle growth while in deficit)
• You're using performance-enhancing drugs (we don't recommend this)

For most people: It's more efficient to choose either cutting (fat loss) OR bulking (muscle gain), not both simultaneously. Trying to do both usually results in spinning your wheels.

No. TDEE is your maintenance level—eating this amount keeps your weight stable.

To lose weight, you must eat below your TDEE (create a calorie deficit).

The only exception: If you calculated your TDEE when sedentary, then significantly increased your activity level (started exercising 5x/week), your new actual TDEE would be higher. Eating at your old calculated TDEE would create a deficit. But this still follows the deficit principle—you'd be eating below your new TDEE.

See How to Use Your TDEE for a complete step-by-step guide on applying TDEE to your goals.

Probably not broken. Common reasons for surprising results:

If TDEE seems TOO HIGH:

• You're taller than average (height significantly affects TDEE)
• You're heavier than you realized (double-check your weight)
• You're male (men have 5-10% higher TDEE than women at same stats)
• You're younger (TDEE decreases ~1-2% per decade after age 30)
• You selected "Very Active" when you should be "Moderately Active"

If TDEE seems TOO LOW:

• You're shorter or lighter than average
• You're female (lower muscle mass on average = lower TDEE)
• You're older (metabolism slows with age)
• You selected "Sedentary" correctly (desk job + no exercise)
• You have a history of yo-yo dieting (metabolic adaptation)

If it still seems off by 500+ calories and you've verified your inputs, you may be in the ~2% where the formula is less accurate. See Calculator Limitations for edge cases.

Common causes (in order of likelihood):

1. Tracking Error (80% of cases)

• Food portions underestimated by 20-50% on average (use a food scale, not eyeballing)
• Not counting cooking oils, butter, dressings (100-200 hidden calories)
• Weekend eating higher than weekdays (erasing weekly deficit)
• Liquid calories not tracked (alcohol, juice, fancy coffee = 300+ calories)
• "Healthy" foods still have calories (nuts, avocado, olive oil are calorie-dense)

2. Water Retention Masking Fat Loss (15% of cases)

• Started new exercise routine (muscles hold water for repair—can mask 2-5 lbs of fat loss)
• High sodium day (eating salty foods causes temporary 2-4 lb water gain)
• Menstrual cycle (women can retain 3-7 lbs of water before period)
• Increased carb intake (each gram of glycogen holds 3g water)

3. Not Enough Time (3% of cases)

• Need 2-3 weeks minimum to see trends (daily fluctuations are normal)
• Weigh yourself same day/time weekly (not daily—too variable)

4. Activity Level Overestimated (1.5% of cases)

• Try dropping to next lower activity category
• 3 gym sessions/week ≠ "Very Active"—that's "Lightly Active"

5. Medical Condition (0.5% of cases)

• Hypothyroidism (get thyroid panel: TSH, Free T3, Free T4)
• PCOS (polycystic ovary syndrome)
• Medications affecting metabolism (antidepressants, beta blockers, corticosteroids)

Recalculate every:

• 10-15 pounds of weight change (up or down—your TDEE changes with your body weight)
• 2-3 months if your activity level changes significantly (started new job, training program, injury, etc.)
• When progress stalls for 3+ weeks despite consistent adherence

Pro Tip: Save your calculator results (use the "Copy Results" button) to track how your TDEE changes over time. This helps you understand your body's trends.

Different calculators use different formulas:

• Mifflin-St Jeor (1990) — Most accurate for 98% of people (what we use)
• Harris-Benedict Revised (1984) — Tends to overestimate by 5-10%
• Katch-McArdle — Requires body fat %, more accurate for very lean individuals
• Cunningham — Similar to Katch-McArdle, requires lean body mass

Results can vary by 200-300 calories between formulas. This is why we default to Mifflin-St Jeor—it has the lowest average error rate according to systematic reviews.

Activity multipliers also vary: Some calculators use different PAL (Physical Activity Level) categories or custom multipliers, which can swing results by 100-200 calories.

Read more about why we chose Mifflin-St Jeor on our Methodology page.

Proceed with caution and medical supervision.

Hypothyroidism (underactive thyroid):

• Can lower TDEE by 5-30% depending on severity
• If properly medicated and TSH is in normal range, calculator may still be reasonably accurate
• If uncontrolled or newly diagnosed, calculator will likely overestimate your TDEE

Hyperthyroidism (overactive thyroid):

• Can increase TDEE by 20-80%
• Calculator will significantly underestimate your calorie needs
• Weight loss may occur even eating at calculated TDEE

More details on medical limitations: Calculator Limitations page

Generally yes for ages 60-75, with the caveat that age-related muscle loss (sarcopenia) can lower actual TDEE below calculated values.

What Changes with Age:

• Metabolism decreases ~1-2% per decade after age 30 (the calculator accounts for this)
• Muscle mass decreases ~3-8% per decade after age 30 (calculator doesn't account for this)
• Activity levels often decrease (make sure to select appropriate activity level)

Ages 75+: Calculator accuracy decreases. We recommend consulting a geriatric nutritionist or your primary care physician for personalized calorie recommendations.

Important: Never eat below 1,200 calories/day (women) or 1,500 calories/day (men) without medical supervision, especially as an older adult. Adequate nutrition becomes even more critical with age.

Yes, slightly. TDEE can increase by approximately 100-300 calories per day during the luteal phase (roughly 1-2 weeks before your period).

Why This Happens:

• Basal body temperature increases by ~0.5°F after ovulation
• Progesterone levels rise, which has a slight thermogenic effect
• Your body is preparing for potential pregnancy (increased metabolic demands)

What This Means Practically:

• Increased hunger/cravings before period are physiologically justified (not just "in your head")
• You may need 100-200 more calories during this phase to feel satisfied
• Weight can fluctuate 2-5 lbs due to water retention (not fat gain)

For weight loss: Weigh yourself the same phase each month (e.g., always Day 5-7 of cycle) for more accurate progress tracking, since water weight can mask fat loss during luteal/menstrual phases.

Possibly yes. Mifflin-St Jeor doesn't account for body composition—it uses total weight, which doesn't distinguish between muscle and fat.

Why Muscle Matters:

• Muscle tissue burns ~6 calories per pound per day at rest
• Fat tissue burns ~2 calories per pound per day at rest
• A very muscular person at 180 lbs burns more than a high-body-fat person at 180 lbs

If you're <15% body fat (men) or <22% body fat (women):

• Consider using the Katch-McArdle formula instead (requires accurate body fat % measurement)
• Or select the next higher activity level as a rough adjustment
• Track results for 2-3 weeks and adjust upward if losing weight too fast

Activity Level Tip: Many athletes underestimate their activity multiplier. If you train 6-7 days/week intensely, "Very Active" or "Extremely Active" is appropriate—don't be afraid to select these if justified.

The multipliers (1.2, 1.375, 1.55, 1.725, 1.9) come from WHO/FAO/UNU expert guidelines on Physical Activity Level (PAL), established through extensive time-motion studies.

How They Were Determined:

• Researchers measured actual total energy expenditure in thousands of individuals using doubly labeled water (the gold standard measurement technique)
• Subjects were categorized by lifestyle patterns (sedentary office work, active occupations, athletes, etc.)
• PAL was calculated as: Total Daily Energy Expenditure ÷ Basal Metabolic Rate
• Average multipliers for each category were established

Full scientific references available on our Sources page.

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How Our Calculator Works:

• All calculations happen in your browser using JavaScript (client-side processing)
• Your age, weight, height, and other inputs never leave your device
• We don't have a database of user data
• We don't require email, account creation, or any personal information

Local Storage (Optional):

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• This is controlled by your browser's cookie/storage settings
• You can clear this anytime via browser settings or private/incognito mode

Full details in our Privacy Policy.

The core TDEE calculator will remain completely free forever. No paywalls, no email capture, no mandatory sign-ups.

Our Commitment:

• Free, instant access to TDEE calculation
• No intrusive ads or popups
• No "unlock full results" schemes
• All formulas and methodologies transparent and publicly documented

Potential Future (Optional) Features:

• Progress tracking (save calculation history—completely optional)
• Meal planning templates (supplementary tools, not required)
• Affiliate links to recommended products (clearly labeled, never required)

If we ever add premium features, the core calculator functionality you use today will always remain free.