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BMR Calculator

Free BMR calculator: Instantly discover calories burned at rest using Mifflin-St Jeor & Harris-Benedict equations. Optimize your nutrition.

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Understanding BMR: Your Body's Calorie Baseline

Basal Metabolic Rate (BMR) represents the minimum number of calories your body needs to perform essential life-sustaining functions while at complete rest. Think of it as your body's "idle" energy consumption—the calories required for breathing, blood circulation, cell production, nutrient processing, and maintaining body temperature when you're doing absolutely nothing.

Our free BMR Calculator uses three scientifically-validated formulas—Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle—to estimate your resting metabolism. Understanding your BMR is fundamental to creating effective nutrition plans, whether you're aiming to lose weight, maintain your current weight, or build muscle. It forms the foundation for calculating your Total Daily Energy Expenditure (TDEE), which guides your daily calorie targets.

BMR typically accounts for 60-75% of your total daily calorie burn, making it the largest component of your energy expenditure. Factors affecting BMR include age, gender, body composition, genetics, hormonal status, and even environmental temperature. This calculator helps you establish a personalized baseline that accounts for your unique characteristics.

💡 Important Note: BMR is not your daily calorie target! Even if you're sedentary, you burn more than BMR through daily activities. Use our TDEE Calculator or Calorie Calculator for actual daily intake recommendations.

When to Use This BMR Calculator

Calculating your Basal Metabolic Rate is valuable in numerous scenarios where understanding your baseline energy needs is essential:

🎯 Weight Loss Planning

Determine the minimum calories your body needs, then create a safe deficit from TDEE (not BMR) for sustainable weight loss without metabolic adaptation.

💪 Muscle Gain Programs

Calculate surplus calories needed above TDEE for lean muscle growth. BMR helps determine baseline metabolism before adding activity and surplus calories.

🍽️ Nutrition Planning

Dietitians and nutritionists use BMR to design personalized meal plans. Knowing BMR ensures recommendations never drop dangerously low.

⚖️ Metabolic Assessment

Compare your calculated BMR to actual weight changes over time. Significant discrepancies may indicate metabolic issues worth discussing with a doctor.

🏋️ Athletic Performance

Athletes use BMR to calculate precise energy needs for training, competition, and recovery. Essential for weight-class sports and endurance activities.

🏥 Medical Contexts

Healthcare providers use BMR to assess metabolic health, set post-surgery nutrition targets, and manage conditions like diabetes or thyroid disorders.

BMR Formulas Explained

Several validated equations calculate BMR, each with specific advantages. This calculator provides three major formulas:

1. Mifflin-St Jeor Equation (1990) - Recommended

Most accurate for modern populations. Considered the gold standard by many nutritionists.

For Men:

$BMR = (10 \times weight_{kg}) + (6.25 \times height_{cm}) - (5 \times age) + 5$

For Women:

$BMR = (10 \times weight_{kg}) + (6.25 \times height_{cm}) - (5 \times age) - 161$

2. Harris-Benedict Equation (Revised 1984)

Original equation from 1919, revised in 1984. Still widely used and reliable.

For Men:

$BMR = 88.362 + (13.397 \times weight_{kg}) + (4.799 \times height_{cm}) - (5.677 \times age)$

For Women:

$BMR = 447.593 + (9.247 \times weight_{kg}) + (3.098 \times height_{cm}) - (4.330 \times age)$

3. Katch-McArdle Formula

Most accurate if you know your lean body mass (requires body fat percentage). Gender-neutral formula.

$BMR = 370 + (21.6 \times LeanBodyMass_{kg})$

Where: LeanBodyMass = TotalWeight × (1 - BodyFat%)

Variable Definitions

VariableDescriptionUnits
WeightYour current body weightKilograms (kg) or Pounds (lbs)
HeightYour standing heightCentimeters (cm) or Inches (in)
AgeYour age in yearsYears
GenderMale or Female (affects hormonal metabolism)Categorical
BMRBasal Metabolic Rate resultCalories per day (kcal/day)

⚠️ Key Differences Between Formulas

  • Mifflin-St Jeor: Most accurate for general population (±10% error), developed from recent data
  • Harris-Benedict: Slightly less accurate but still reliable, may overestimate for obese individuals
  • Katch-McArdle: Best for athletes/lean individuals, requires body fat measurement
  • All formulas have ±10-15% error margin for individuals—use as starting estimates

Step-by-Step: How to Calculate Your BMR

1

Gather Accurate Measurements

Record your current weight (use a scale), height (measure barefoot), age, and gender. For most accurate results, weigh yourself in the morning before eating.

2

Select Your Formula Preference

Choose Mifflin-St Jeor for most accurate general results. Use Harris-Benedict for comparison. Select Katch-McArdle only if you have accurate body fat percentage data.

3

Input Your Data

Enter your measurements into the calculator. Double-check values for accuracy—even small errors in weight or height can affect results by 50-100 calories.

4

Review Your BMR Results

The calculator shows BMR values from different formulas. Most people's BMR falls between 1,200-2,000 cal/day. Women typically range 1,200-1,500; men 1,500-2,000.

5

Calculate Your TDEE

Multiply BMR by your activity factor: Sedentary (1.2), Lightly Active (1.375), Moderately Active (1.55), Very Active (1.725), Extremely Active (1.9). This gives your Total Daily Energy Expenditure. Use our TDEE Calculator for this.

6

Set Your Calorie Goals

Weight Loss: TDEE - 500 calories (1 lb/week loss)
Maintenance: TDEE calories
Muscle Gain: TDEE + 300-500 calories
Never eat below BMR long-term! It can damage metabolism.

7

Track and Adjust

Monitor weight changes for 2-3 weeks. If results don't match expectations, adjust calories by 100-200. Individual metabolism varies ±10-15% from formulas.

Worked Examples: Real BMR Calculations

Let's calculate BMR for different individuals using all three formulas to see how results compare:

Example 1: Average Adult Male

Given:

  • Gender: Male
  • Age: 35 years
  • Height: 5'10" (178 cm)
  • Weight: 180 lbs (82 kg)

Calculations:

Mifflin-St Jeor:
= (10 × 82) + (6.25 × 178) - (5 × 35) + 5
= 820 + 1,113 - 175 + 5 = 1,763 cal/day

Harris-Benedict:
= 88.362 + (13.397 × 82) + (4.799 × 178) - (5.677 × 35)
= 1,791 cal/day

Result: BMR ≈ 1,763-1,791 cal/day

Interpretation: If sedentary (office job), TDEE ≈ 2,116 cal (BMR × 1.2). For 1 lb/week weight loss, target 1,616 cal/day. Never drop below BMR (1,763) long-term.

Example 2: Active Female

Given:

  • Gender: Female
  • Age: 28 years
  • Height: 5'5" (165 cm)
  • Weight: 140 lbs (64 kg)

Calculations:

Mifflin-St Jeor:
= (10 × 64) + (6.25 × 165) - (5 × 28) - 161
= 640 + 1,031 - 140 - 161 = 1,370 cal/day

Harris-Benedict:
= 447.593 + (9.247 × 64) + (3.098 × 165) - (4.330 × 28)
= 1,398 cal/day

Result: BMR ≈ 1,370-1,398 cal/day

Interpretation: If moderately active (exercises 3-5 days/week), TDEE ≈ 2,124 cal (BMR × 1.55). For maintenance, eat 2,124 cal. For muscle gain, 2,424 cal.

Example 3: Older Male

Given:

  • Gender: Male
  • Age: 65 years
  • Height: 5'9" (175 cm)
  • Weight: 170 lbs (77 kg)

Calculations:

Mifflin-St Jeor:
= (10 × 77) + (6.25 × 175) - (5 × 65) + 5
= 770 + 1,094 - 325 + 5 = 1,544 cal/day

Result: BMR ≈ 1,544 cal/day

Interpretation: Notice BMR is lower due to age (metabolism slows 1-2% per decade after 30). Age factor reduces BMR by ~150 cal compared to a 35-year-old with same stats. Maintaining muscle mass through strength training helps minimize this decline.

Example 4: Young Athletic Male

Given:

  • Gender: Male
  • Age: 22 years
  • Height: 6'1" (185 cm)
  • Weight: 195 lbs (88 kg)
  • Body Fat: 12% (for Katch-McArdle)

Calculations:

Mifflin-St Jeor:
= (10 × 88) + (6.25 × 185) - (5 × 22) + 5
= 1,881 cal/day

Katch-McArdle:
LBM = 88 × (1 - 0.12) = 77.4 kg
BMR = 370 + (21.6 × 77.4) = 2,042 cal/day

Result: BMR ≈ 1,881-2,042 cal/day

Interpretation: Katch-McArdle gives higher BMR because it accounts for high lean mass. For an athlete training 6-7 days/week (activity 1.725), TDEE ≈ 3,522 cal. Needs 3,822-4,022 cal for muscle gain.

Example 5: Petite Female

Given:

  • Gender: Female
  • Age: 30 years
  • Height: 5'2" (157 cm)
  • Weight: 115 lbs (52 kg)

Calculations:

Mifflin-St Jeor:
= (10 × 52) + (6.25 × 157) - (5 × 30) - 161
= 520 + 981 - 150 - 161 = 1,190 cal/day

Result: BMR ≈ 1,190 cal/day

Interpretation: Smaller individuals have lower BMR. If sedentary, TDEE ≈ 1,428 cal. For healthy weight loss (0.5 lb/week), target 1,178 cal—very close to BMR! This is why petite women find weight loss challenging. Increasing activity is often more effective than extreme calorie restriction.

💡 Key Takeaway: BMR varies significantly by age, size, gender, and body composition. These examples show typical ranges, but individual metabolism can differ by ±10-15%. Always use BMR as a starting estimate and adjust based on real-world results.

Practical Applications of BMR

Understanding your Basal Metabolic Rate has crucial real-world applications across fitness, nutrition, and health management:

🎯 Precision Weight Loss

BMR establishes your metabolic floor—never diet below this value long-term. Calculate TDEE from BMR, then subtract 500 calories for safe 1 lb/week loss. Prevents metabolic adaptation and muscle loss that occurs with extreme restriction.

💪 Lean Muscle Building

Bodybuilders use BMR to calculate precise surplus calories (TDEE + 300-500) for muscle gain without excessive fat. Higher BMR from increased muscle mass means you can eat more while maintaining weight.

🩺 Clinical Nutrition

Hospitals and clinics use BMR to determine nutrition support for patients recovering from surgery, illness, or eating disorders. Ensures adequate calorie intake for healing without overfeeding.

🏃 Athletic Performance

Endurance athletes multiply BMR by activity factors (1.5-2.0) to determine massive calorie needs (often 3,000-5,000 cal/day). Prevents under-fueling that impairs performance and recovery.

⚖️ Metabolic Health Assessment

Comparing calculated BMR to actual calorie needs reveals metabolic efficiency. Significant discrepancies may indicate thyroid issues, PCOS, or metabolic adaptation warranting medical evaluation.

📊 Body Recomposition

For simultaneous fat loss and muscle gain, eat slightly below TDEE (never below BMR) with high protein (1.6-2.2g per kg). Use Macro Calculator to optimize ratios.

🤰 Pregnancy & Postpartum

Pre-pregnancy BMR helps set appropriate calorie increases during pregnancy (300-500 extra calories in 2nd/3rd trimesters). Postpartum, BMR guides safe weight loss while maintaining milk supply if breastfeeding.

🧬 Aging & Longevity

Tracking BMR changes with age helps detect muscle loss early. Strength training preserves BMR by maintaining muscle mass, supporting metabolic health and independence in older adults.

✨ How to Boost Your BMR Naturally

  • Build Muscle: Muscle burns 2-3× more calories at rest than fat. Strength train 2-4× per week.
  • Eat Enough Protein: High protein (1.6-2.2g per kg) has highest thermic effect (20-30% of calories burned in digestion).
  • Stay Hydrated: Dehydration can slow metabolism by 2-3%. Drink at least 8 cups daily—use our Water Intake Calculator.
  • Get Quality Sleep: Poor sleep disrupts hormones (leptin, ghrelin, cortisol) and can lower BMR by 5-10%.
  • Avoid Extreme Deficits: Eating well below BMR triggers metabolic adaptation (slower metabolism). Stay above BMR.
  • Try HIIT: High-intensity interval training creates "afterburn effect" (EPOC), elevating metabolism for 24-48 hours post-workout.

Common BMR Calculation Mistakes

Avoid these frequent errors that lead to inaccurate BMR estimates and poor nutrition planning:

❌ Confusing BMR with TDEE or Daily Calorie Target

Consequence: BMR is calories burned at complete rest. Eating only BMR calories when you're active leads to severe undereating, metabolic slowdown, muscle loss, hormonal imbalances, and nutrient deficiencies. Even sedentary people need more than BMR.

✓ Solution: Use BMR as a baseline. Calculate TDEE (BMR × activity factor 1.2-1.9) for actual daily needs. For weight loss, eat TDEE - 500, never below BMR long-term.

❌ Not Accounting for Individual Metabolic Variation

Consequence: BMR formulas have ±10-15% error for individuals. Some people have naturally faster or slower metabolism due to genetics, thyroid function, medications, or previous dieting history. Blindly following calculator numbers leads to frustration when results don't match.

✓ Solution: Use BMR as starting estimate. Track weight for 2-3 weeks. If losing/gaining faster or slower than expected, adjust calories by 100-200. Your actual metabolism may differ from the formula.

❌ Using Inaccurate Body Measurements

Consequence: Wrong weight (wearing clothes, after eating, evening vs morning) or height (with shoes, slouching) skews BMR by 50-150 calories. Using old measurements from years ago when you were heavier/lighter compounds errors.

✓ Solution: Weigh barefoot in underwear, morning before eating, on flat surface. Measure height barefoot against wall. Use current measurements (within 1 month). Recalculate BMR every 10+ lbs weight change.

❌ Ignoring Medical Conditions Affecting Metabolism

Consequence: Hypothyroidism can lower BMR by 20-40%. PCOS, diabetes, certain antidepressants, steroids, and hormonal birth control all affect metabolism. Calculator assumes normal metabolic function, leading to inaccurate estimates.

✓ Solution: If you have metabolic conditions or take medications affecting metabolism, consult doctor or dietitian for personalized assessment. Consider indirect calorimetry test for accurate measurement.

❌ Forgetting to Recalculate as You Lose/Gain Weight

Consequence: BMR decreases as you lose weight (lighter body requires fewer calories). Using original BMR after losing 20 lbs means you're eating too much, stalling progress. Similarly, BMR increases with weight/muscle gain.

✓ Solution: Recalculate BMR every 10-15 lbs weight change or every 2-3 months. Adjust calorie targets accordingly. Weight loss plateaus often indicate need for BMR recalculation.

❌ Choosing Wrong Formula for Your Situation

Consequence: Using Katch-McArdle without knowing accurate body fat percentage gives wrong results. Using any formula for obese individuals (BMI >35) may overestimate BMR. Not all formulas suit all populations.

✓ Solution: Use Mifflin-St Jeor for general population (most accurate). Only use Katch-McArdle if you have DEXA-scan or professional body fat measurement. For obesity, consider adjusted formulas or professional consultation.

Frequently Asked Questions About BMR

Comprehensive answers to common questions about Basal Metabolic Rate:

What is BMR and why is it important?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to maintain vital functions like breathing, blood circulation, cell production, nutrient processing, and maintaining body temperature. It represents 60-75% of your total daily calorie expenditure.

Understanding your BMR is crucial for:

  • Setting accurate calorie targets for weight loss, maintenance, or muscle gain
  • Ensuring you never eat dangerously low (below BMR long-term can damage metabolism)
  • Understanding how age, gender, and body composition affect energy needs
  • Creating effective nutrition plans with dietitians or trainers

BMR is the foundation—multiply it by your activity level to get TDEE (total daily calories you actually need).

What's the difference between BMR and TDEE?

BMR (Basal Metabolic Rate): Calories burned at complete rest—sleeping, lying down, no activity whatsoever. Just keeping your body alive.

TDEE (Total Daily Energy Expenditure): Total calories you burn in a day including all activity—walking, working, exercising, fidgeting, digesting food, etc.

The relationship: TDEE = BMR × Activity Factor

  • Sedentary (desk job, no exercise): BMR × 1.2
  • Lightly active (1-3 days/week): BMR × 1.375
  • Moderately active (3-5 days/week): BMR × 1.55
  • Very active (6-7 days/week): BMR × 1.725
  • Extremely active (athlete, physical job): BMR × 1.9

Critical: Eat at TDEE for maintenance, TDEE - 500 for weight loss. Never eat at BMR unless bedridden—even sedentary people need more than BMR!

Which BMR formula is most accurate?

Mifflin-St Jeor (1990): Currently considered most accurate for general population. Developed from recent data, includes age, gender, height, weight. Accuracy within ±10% for most people. Recommended for most users.

Harris-Benedict (Revised 1984): Traditional formula, still reliable. Original from 1919, revised in 1984. May slightly overestimate for obese individuals. Good for comparison with Mifflin-St Jeor.

Katch-McArdle: Most accurate if you have precise lean body mass data (from DEXA scan or bod pod). Gender-neutral formula accounts for muscle mass. Only use if you have professional body fat measurement—estimating body fat makes it less accurate than Mifflin.

Bottom line: Use Mifflin-St Jeor unless you have accurate body composition data, then try Katch-McArdle. All formulas have ±10-15% individual variation.

Can I eat below my BMR to lose weight faster?

Short answer: No, not long-term. Eating significantly below BMR triggers multiple negative effects:

  • Metabolic adaptation: Your metabolism slows down to conserve energy (adaptive thermogenesis)
  • Muscle loss: Body breaks down muscle for energy, lowering BMR further
  • Hormonal disruption: Thyroid hormone decreases, cortisol increases, leptin drops
  • Nutrient deficiencies: Hard to get adequate vitamins/minerals on very low calories
  • Energy crashes: Fatigue, poor workout performance, brain fog
  • Rebound weight gain: Slower metabolism makes weight regain likely when calories increase

Safe approach: Calculate TDEE (BMR × activity factor). Subtract 500 calories for 1 lb/week loss, or 750 for 1.5 lbs/week. Never go below BMR for extended periods. Use our Calorie Calculator for proper targets.

How can I increase my BMR naturally?

Several evidence-based strategies can boost your Basal Metabolic Rate:

1. Build Muscle Mass: Muscle tissue burns 2-3× more calories at rest than fat. Strength train 2-4× per week. Gaining 5 lbs muscle increases BMR by ~30-50 cal/day.

2. Eat Adequate Protein: Protein has highest thermic effect of food (TEF)—you burn 20-30% of protein calories just digesting it. Aim for 1.6-2.2g per kg body weight. Use our Macro Calculator.

3. Don't Under-Eat: Severe calorie restriction (below BMR) lowers metabolism. Eat at reasonable deficit from TDEE, not BMR.

4. Stay Hydrated: Dehydration slows cellular processes. Drink 8-12 cups water daily—check our Water Intake Calculator.

5. Sleep 7-9 Hours: Poor sleep disrupts leptin, ghrelin, thyroid hormones, lowering BMR by 5-10%.

6. HIIT Training: High-intensity interval training creates "afterburn effect" (EPOC), elevating metabolism 24-48 hours post-workout.

7. Manage Stress: Chronic high cortisol promotes muscle breakdown and fat storage, lowering BMR over time.

Reality check: Genetics determine 20-30% of BMR variation. You can optimize within your range but can't dramatically change your baseline.

Does age really slow down metabolism?

Yes, BMR decreases approximately 1-2% per decade after age 30, but it's not inevitable decline:

Why metabolism slows:

  • Muscle loss (sarcopenia): People lose 3-8% muscle mass per decade after 30 if inactive
  • Decreased activity: Older adults tend to be less active, further reducing muscle
  • Hormonal changes: Thyroid hormone, growth hormone, testosterone gradually decline
  • Cellular changes: Mitochondrial efficiency decreases slightly with age

The good news: The decline is primarily from muscle loss, NOT age itself. Older adults who maintain muscle mass through strength training have BMR similar to younger people of same size.

Prevention: Lift weights 2-3× per week, eat adequate protein (1.2-1.6g per kg for older adults), stay active. You can largely prevent metabolic decline.

Is my BMR affected by medical conditions?

Yes, several medical conditions significantly affect BMR:

Hypothyroidism (underactive thyroid): Can lower BMR by 20-40%. Thyroid hormone regulates metabolism.

Hyperthyroidism (overactive thyroid): Increases BMR by 30-60%, causing unintentional weight loss despite eating more.

PCOS (Polycystic Ovary Syndrome): Insulin resistance and hormonal imbalances can lower BMR by 5-15%.

Diabetes: Insulin resistance affects glucose metabolism and can impact BMR.

Cushing's Syndrome: Excess cortisol promotes muscle loss and fat gain, lowering BMR.

Medications that affect BMR:

  • Antidepressants (SSRIs, tricyclics): May lower metabolism
  • Corticosteroids: Promote muscle loss
  • Beta-blockers: Can reduce BMR slightly
  • Antipsychotics: Often slow metabolism
  • Hormonal birth control: Variable effects on metabolism

Action: If your actual calorie needs seem very different from calculated BMR (±20%+), or you can't lose weight despite significant deficit, consult a doctor. Request thyroid panel (TSH, T3, T4), fasting insulin, and metabolic testing.

How accurate are BMR calculators?

BMR formulas have a margin of error of ±10-15% for individuals, though they're accurate for population averages.

Why individual variation exists:

  • Genetics: Some people naturally have faster/slower metabolism (20-30% variation)
  • Body composition: Formulas don't account for muscle vs fat ratio (except Katch-McArdle)
  • Medical conditions: Thyroid, PCOS, diabetes affect metabolism
  • Medications: Many drugs alter metabolic rate
  • Previous dieting history: Repeated dieting can cause metabolic adaptation
  • Ethnicity: Some populations have slightly different metabolic rates

More accurate options:

  • Indirect calorimetry: Measures oxygen consumption/CO2 production. Accuracy ±3-5%. Available at universities, research centers, some gyms.
  • Metabolic chamber: Gold standard, measures 24-hour energy expenditure. Research setting only.

Practical approach: Use calculator BMR as starting estimate. Track weight/energy for 2-3 weeks. Adjust calories by 100-200 based on actual results. Your body's response is more accurate than any formula.

How often should I recalculate my BMR?

Recalculate BMR in these situations:

  • Every 10-15 lbs weight change: BMR decreases with weight loss, increases with gain
  • Every 2-3 months during active weight loss/gain: Ensures targets remain accurate
  • After building significant muscle: Increased muscle mass raises BMR
  • If weight loss plateaus for 3+ weeks: May indicate need for recalculation and adjustment
  • Major age milestones: Every 5-10 years to account for age-related changes
  • After pregnancy or major health changes: Body composition and metabolism shift

Example: You start at 200 lbs with BMR 1,900. After losing 30 lbs to 170 lbs, BMR drops to ~1,700. If you keep eating for 1,900 BMR, you'll stop losing weight. Recalculate and adjust deficit from new BMR.

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Conclusion: Understanding Your Metabolic Baseline

Your Basal Metabolic Rate is the foundation of effective nutrition planning. It represents the minimum energy your body needs just to stay alive—breathing, circulating blood, producing cells, and maintaining temperature. Understanding your BMR helps you set realistic, safe calorie targets that support your health goals without triggering metabolic damage.

Remember that BMR is not your daily calorie target. Even sedentary individuals burn significantly more than BMR through daily activities. Use BMR to calculate TDEE (BMR × activity factor 1.2-1.9), then set your nutrition targets from there. For weight loss, subtract 500 calories from TDEE, not BMR. For muscle gain, add 300-500 to TDEE. Never eat below BMR for extended periods—it can slow your metabolism and compromise health.

BMR calculations provide estimates within ±10-15% accuracy. Use them as starting points, then adjust based on real-world results over 2-3 weeks. Your body's response—weight changes, energy levels, workout performance—is more important than any formula. Factors like genetics, medical conditions, medications, and previous dieting history create significant individual variation.

Finally, remember that while you can't dramatically change your genetic baseline, you can optimize BMR by building muscle mass, eating adequate protein, staying hydrated, getting quality sleep, and avoiding extreme calorie restriction. These strategies not only support higher BMR but also improve overall health, energy, and quality of life.

🎯 Next Steps: Now that you know your BMR, use our TDEE Calculator to determine actual daily calorie needs, then the Macro Calculator to break down into protein, carbs, and fats. Create a complete, science-based nutrition plan tailored to your metabolism!

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