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Step 1: Calculate BMR (Mifflin-St Jeor Equation)

Step 2: Apply Activity Multiplier to Get Maintenance

Maintaining Current Weight

To keep weight stable, consume exactly your maintenance calories daily. This balances energy intake with expenditure. However, perfect precision isn't necessary—staying within ±100-200 calories of maintenance still maintains weight. Daily weight fluctuates 2-5 pounds from water retention, food volume, and hormones, so track weekly averages, not daily weigh-ins. If weight trends up/down over 2-3 weeks, adjust calories by 100-200 in the opposite direction.

Creating a Deficit for Weight Loss

For fat loss, eat below maintenance calories. A 500 cal/day deficit creates ~1 pound weekly loss; 1,000 cal/day deficit targets ~2 pounds weekly. For maintenance of 2,500 cal/day: eat 2,000 cal/day for 1 lb/week loss or 1,500 cal/day for 2 lb/week loss. Moderate deficits (500-750 cal) are sustainable; aggressive deficits (1,000+ cal) risk muscle loss and metabolic slowdown. Never eat below 1,200 cal/day (women) or 1,500 cal/day (men) without medical supervision.

Creating a Surplus for Muscle Gain

For muscle building, eat above maintenance calories. A 250-500 cal/day surplus supports lean muscle gain with resistance training (~0.5-1 pound weekly gain). Larger surpluses accelerate weight gain but increase fat accumulation. For maintenance of 2,500 cal/day: eat 2,750-3,000 cal/day for lean bulking. Without strength training, surplus calories become predominantly fat. Prioritize protein (1.6-2.2 g/kg bodyweight) to optimize muscle protein synthesis during bulking.

Diet Breaks at Maintenance

Diet breaks involve eating at maintenance calories for 1-2 weeks after 8-12 weeks of dieting. This temporarily restores leptin, thyroid hormones, and metabolic function suppressed during prolonged deficits. Diet breaks reduce hunger, improve gym performance, prevent metabolic adaptation, and provide psychological relief from restriction. After the break, return to calorie deficit with renewed adherence and potentially higher maintenance calories than before the break due to hormonal recovery.

Weight Loss Decreases Maintenance

Smaller bodies require fewer calories to maintain. Losing 20 pounds typically decreases maintenance by 100-300 cal/day. A person who maintains at 2,500 calories at 200 pounds might only need 2,200-2,300 calories at 180 pounds. This explains weight loss plateaus—initial deficit becomes maintenance as weight drops. Recalculate maintenance every 10-15 pounds lost and adjust calorie intake downward to continue losing, or accept slower progress at higher calorie intake.

Muscle Gain Increases Maintenance

Muscle tissue burns more calories than fat—approximately 6 cal/lb/day vs. 2 cal/lb/day for fat. Gaining 10 pounds of muscle increases maintenance by 40-100 cal/day, making weight maintenance easier long-term. This is why strength training is crucial: building muscle permanently elevates maintenance calories, providing more dietary flexibility without weight gain. Conversely, losing muscle during calorie restriction lowers maintenance, contributing to post-diet weight regain.

Metabolic Adaptation During Dieting

During prolonged calorie restriction, maintenance calories decrease beyond what's expected from weight loss alone—sometimes 200-500 cal below predicted levels. This "adaptive thermogenesis" is survival mechanism: BMR decreases, NEAT drops (less fidgeting, lower body temperature), and exercise becomes less efficient. This is why plateaus occur despite maintaining deficit. Combat adaptation with moderate deficits, diet breaks every 8-12 weeks, adequate protein, resistance training, and sufficient sleep.

Age-Related Decline

Maintenance calories decrease 1-2% per decade after age 30, primarily from muscle loss (sarcopenia), hormonal changes (declining testosterone, estrogen, growth hormone), and reduced spontaneous activity. A 50-year-old may have 200-400 cal/day lower maintenance than their 20-year-old self at identical weight. However, this decline isn't inevitable—maintaining muscle through resistance training and staying active preserves maintenance calories despite aging. Active 60-year-olds can have higher maintenance than sedentary 30-year-olds.

Activity Level Changes

Changing exercise habits significantly alters maintenance. Starting a running program (burning 300-500 cal per session, 3-4x weekly) increases weekly expenditure by 900-2,000 calories—raising daily maintenance by 130-290 cal/day. Conversely, becoming less active (stopping gym membership, switching to desk job) can decrease maintenance by 200-500 cal/day. When exercise habits change, recalculate maintenance and adjust food intake accordingly to avoid unintended weight changes.