How Many Calories Should I Eat to Lose Weight? A Real Number, With the Math

Key Takeaways

• For most adults, eat 500 calories per day below your maintenance level to lose about 1 pound per week.
• Maintenance is roughly bodyweight in pounds times 14 to 16 for sedentary, 16 to 18 for moderately active.
• A 180 lb sedentary woman maintains around 2,520 calories and would target 2,000 for steady weight loss.
• A pound of body fat stores roughly 3,500 calories of usable energy.
• To lose a pound of fat, you have to create a 3,500-calorie deficit between what you eat and what your body burns.

Direct answer (40-60 words, snippet-optimized)

For most adults, eat 500 calories per day below your maintenance level to lose about 1 pound per week. Maintenance is roughly bodyweight in pounds times 14 to 16 for sedentary, 16 to 18 for moderately active. A 180 lb sedentary woman maintains around 2,520 calories and would target 2,000 for steady weight loss.

Table of contents

1. The 30-second answer
2. The calorie math: why a pound equals 3,500 calories
3. How to find your maintenance calories in 2 minutes
4. The 500-calorie deficit rule and where it breaks
5. Worked examples for different bodies
6. Calorie targets table by weight, sex, and activity
7. The minimum calorie floor (don't go below this)
8. How protein, fiber, and meal timing change the math
9. How GLP-1 medications change the calorie equation
10. Why most calorie calculators are slightly wrong
11. Common mistakes that stall weight loss
12. FAQ
13. Footer disclaimers

The calorie math: why a pound equals 3,500 calories

A pound of body fat stores roughly 3,500 calories of usable energy. To lose a pound of fat, you have to create a 3,500-calorie deficit between what you eat and what your body burns. Spread that over a week, and a 500-calorie daily deficit produces about 1 pound of fat loss per week.

This number comes from work originally published by Max Wishnofsky in 1958 (American Journal of Clinical Nutrition). Modern research (Hall et al., Lancet, 2011) refined the model: actual fat loss is closer to 75 to 80% of the deficit because some of the lost weight is water, glycogen, and a small amount of lean tissue. The 3,500-calorie rule holds well as a planning estimate.

The math has three components:

1. What you burn (TDEE): Total Daily Energy Expenditure, which includes your resting metabolic rate plus activity
2. What you eat (intake): total calories consumed
3. The deficit (TDEE minus intake): the gap that drives weight loss

Get TDEE roughly right, eat below it, and the scale moves.

How to find your maintenance calories in 2 minutes

The cleanest method is the Mifflin-St Jeor equation, which the American Dietetic Association and most clinicians use as their baseline.

For men: RMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5

For women: RMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161

Then multiply by an activity factor:

• 1.2 = sedentary (desk job, no exercise)
• 1.375 = lightly active (light exercise 1 to 3 days/week)
• 1.55 = moderately active (exercise 3 to 5 days/week)
• 1.725 = very active (hard exercise 6 to 7 days/week)
• 1.9 = extremely active (physical job plus daily training)

The result is your TDEE, your maintenance calories.

If you don't want to do math, here's a working shortcut accurate to within about 10%:

• Sedentary: bodyweight in pounds × 14
• Lightly active: bodyweight in pounds × 15
• Moderately active: bodyweight in pounds × 16
• Very active: bodyweight in pounds × 17
• Athlete: bodyweight in pounds × 18 to 20

A 180 lb woman with a desk job: 180 × 14 = 2,520 calories maintenance. A 220 lb man who lifts 4x/week: 220 × 16 = 3,520 calories maintenance.

The 500-calorie deficit rule and where it breaks

For most people, a 500-calorie daily deficit is the sweet spot. It produces about 1 pound of weight loss per week, is sustainable for several months, and doesn't cause the muscle loss or metabolic slowdown that comes with deeper cuts.

A larger deficit isn't always better. Three things go wrong with deeper cuts:

1. Muscle loss accelerates. Below about a 750-calorie deficit, lean tissue loss climbs sharply. A 2017 study (Longland et al., American Journal of Clinical Nutrition) showed that subjects on a deep deficit lost 1.6 kg of muscle vs 0.3 kg in a moderate deficit group, even with high protein.

2. Adaptive thermogenesis kicks in. Resting metabolic rate falls more than the math predicts when calories drop too low. The body conserves energy by reducing non-exercise activity (NEAT) and dropping thyroid hormone output. The cut becomes less effective the longer you stay on it.

3. Adherence collapses. Below about 1,500 calories for men and 1,200 for women, hunger and food preoccupation make consistent intake nearly impossible. Dropouts in clinical weight-loss trials are 2 to 3 times higher in deep-deficit arms.

The deficit guideline:

• Lose 0.5 lb per week: 250-calorie daily deficit (most patient, most sustainable)
• Lose 1 lb per week: 500-calorie daily deficit (the standard recommendation)
• Lose 1.5 lb per week: 750-calorie daily deficit (works short-term, harder to sustain)
• Lose 2 lb per week: 1,000-calorie daily deficit (only sustainable for higher BMI patients)

The faster you try to go, the more important protein, sleep, and resistance training become. We'll get there.

Worked examples for different bodies

Example 1: 35-year-old woman, 5'5", 175 lb, sedentary office job, wants to lose 25 lb.

• Mifflin-St Jeor RMR: (10 × 79.4) + (6.25 × 165.1) - (5 × 35) - 161 = 1,490 cal
• TDEE at sedentary (×1.2): 1,788 cal
• 500 cal deficit target: 1,288 cal/day
• Adjusted to floor (1,200 minimum): 1,300 cal/day
• Expected loss: roughly 0.9 lb/week
• Time to goal: 27 to 32 weeks

Example 2: 42-year-old man, 6'1", 245 lb, moderately active (lifts 3x/week), wants to lose 35 lb.

• Mifflin-St Jeor RMR: (10 × 111) + (6.25 × 185.4) - (5 × 42) + 5 = 2,066 cal
• TDEE at moderate (×1.55): 3,202 cal
• 750 cal deficit target: 2,452 cal/day
• Expected loss: roughly 1.5 lb/week
• Time to goal: 22 to 26 weeks

Example 3: 28-year-old woman, 5'2", 145 lb, very active (CrossFit 5x/week), wants to lose 10 lb.

• Mifflin-St Jeor RMR: (10 × 65.8) + (6.25 × 157.5) - (5 × 28) - 161 = 1,341 cal
• TDEE at very active (×1.725): 2,313 cal
• 250 cal deficit target: 2,063 cal/day
• Expected loss: roughly 0.5 lb/week
• Time to goal: 18 to 22 weeks

The same target weight loss can take 18 weeks or 32 weeks depending on body size and activity. The faster timelines aren't necessarily better. Slower loss preserves more muscle and is more likely to stay off.

Calorie targets table by weight, sex, and activity

A quick-reference table for sedentary to moderately active adults aiming for 1 lb/week loss:

Current weight	Sedentary woman	Lightly active woman	Sedentary man	Lightly active man
130 lb	1,300 cal	1,400 cal	1,500 cal	1,650 cal
150 lb	1,400 cal	1,500 cal	1,650 cal	1,800 cal
175 lb	1,500 cal	1,650 cal	1,825 cal	2,000 cal
200 lb	1,650 cal	1,800 cal	2,000 cal	2,200 cal
225 lb	1,800 cal	1,950 cal	2,200 cal	2,400 cal
250 lb	2,000 cal	2,150 cal	2,400 cal	2,600 cal
275 lb	2,150 cal	2,300 cal	2,600 cal	2,800 cal
300 lb	2,300 cal	2,500 cal	2,800 cal	3,000 cal

These numbers assume a 500 cal/day deficit from estimated maintenance. Heavier patients have more flexibility because their maintenance is higher.

The numbers are estimates. Track your weight weekly for 2 to 3 weeks at the target intake. If the scale isn't moving, drop another 100 to 200 cal. If it's moving too fast (over 1.5 lb/week sustained), add 100 to 200 cal back.

The minimum calorie floor (don't go below this)

The American College of Sports Medicine and the Academy of Nutrition and Dietetics recommend not eating below:

• 1,200 calories per day for women
• 1,500 calories per day for men

These floors aren't arbitrary. They are the levels at which most adults can hit basic micronutrient targets (iron, calcium, magnesium, B vitamins) from whole food. Below the floor, supplementation becomes mandatory and meal planning becomes very tight.

Medically supervised very-low-calorie diets (VLCDs) at 800 calories or less exist for severe obesity (BMI 40+). They use shake-based meal replacements with full micronutrient profiles, and they require physician oversight to monitor for gallstones, electrolyte imbalances, and arrhythmias.

For self-directed weight loss, stay above the floor. If your calculated target falls below it (common for short, older, sedentary women trying to lose 20+ lb), set the target at the floor and accept slower loss, or add resistance training to raise your TDEE.

How protein, fiber, and meal timing change the math

Calories are the primary driver of weight loss, but composition matters for body composition and adherence.

Protein. Higher protein intake during a deficit preserves muscle mass and increases satiety. The clinically supported target is 0.7 to 1.0 grams per pound of bodyweight, which is higher than the RDA. For a 180 lb person, that's 126 to 180 g of protein daily.

A 2017 meta-analysis (Helms et al., International Journal of Sport Nutrition and Exercise Metabolism) found that subjects in a 500-calorie deficit with 1.0 g/lb protein intake retained 10% more lean mass than subjects with the standard 0.4 g/lb intake.

Protein also has the highest thermic effect of food (TEF) of the macronutrients: about 25 to 30% of protein calories are burned during digestion vs 5 to 10% for carbs and 0 to 3% for fat. A high-protein 1,800 cal diet effectively delivers about 1,700 net calories.

Fiber. Fiber slows gastric emptying, blunts blood sugar spikes, and increases satiety per calorie. Aim for 25 to 35 g daily from whole-food sources (vegetables, fruit, beans, whole grains). Most American adults eat 12 to 15 g.

Meal timing. Total daily calories matter more than timing. Studies of intermittent fasting (Trepanowski et al., JAMA Internal Medicine, 2017) show that 16:8 or 5:2 fasting protocols produce weight loss equivalent to standard daily-deficit dieting, neither better nor worse. Choose the eating window that's most sustainable for you.

Sleep. This is the part most calorie-counting articles skip. Sleeping less than 6 hours per night raises ghrelin (the hunger hormone) and lowers leptin (the satiety hormone). A 2010 study (Nedeltcheva et al., Annals of Internal Medicine) showed that subjects on a deficit who slept 5.5 hours lost 55% less fat and 60% more lean mass than subjects who slept 8.5 hours, despite identical calorie intake.

Sleep is a calorie multiplier. Get 7 to 9 hours.

How GLP-1 medications change the calorie equation

GLP-1 medications like semaglutide and tirzepatide work by reducing appetite and slowing gastric emptying. The functional effect is that patients eat 20 to 30% fewer calories without consciously trying.

For a patient with a 2,400 calorie maintenance level, a GLP-1 typically produces a 500 to 700 calorie spontaneous deficit. That's the same deficit a non-medicated patient would need to enforce through tracking and willpower.

What this changes:

• You don't need to count as obsessively. Most patients on GLP-1s naturally land at a sustainable deficit.
• Protein becomes more important, not less. Reduced appetite means it's easy to under-eat protein and lose more muscle than fat. Hit the 0.7 to 1.0 g/lb target even if it means scheduling protein meals.
• The floor still applies. Eating under 1,200 cal (women) or 1,500 cal (men) for extended periods is unhealthy on or off medication. If you're consistently below, talk to your provider.
• Hydration becomes harder. Reduced food intake means less water from food, and many patients forget to drink. Aim for half your bodyweight in ounces daily as a baseline.

The SURMOUNT-1 trial (Jastreboff et al., NEJM, 2022) showed average weight loss of 22.5% over 72 weeks on tirzepatide 15 mg, compared to 2.4% on placebo. The mechanism is calorie reduction. The medication makes the deficit easier to sustain, not different in kind.

Why most calorie calculators are slightly wrong

Online calorie calculators give you a single number. The number is a starting estimate, not a precise prescription. Three reasons:

1. The equations are population averages. Mifflin-St Jeor was validated against indirect calorimetry in healthy adults of typical body composition. If you have unusually high or low muscle mass, the equation is off by 5 to 15%. Bodybuilders systematically have higher RMR than predicted; patients with sarcopenia have lower.

2. Activity factors are blunt. The five-tier activity scale (sedentary to extremely active) is a rough sort. A construction worker who goes to the gym is "very active." A nurse who's on her feet 12 hours but isn't formally exercising is also "very active." Their actual TDEE differs by 300 to 500 calories.

3. Food labels can be off. FDA rules allow food labels to be inaccurate by up to 20%. A "200 calorie" granola bar might be 240. Restaurant meals are even less reliable. Frequent calorie-tracking errors compound: a 10% systematic overestimation of intake erases a 250 calorie deficit.

The fix isn't more precise calculators. It's monitoring outcomes. Weigh in weekly, track 7-day average. If you're losing as predicted, your numbers work. If you're not, adjust by 100 to 200 calories and watch another 2 weeks. The scale tells you what's true.

Common mistakes that stall weight loss

1. Underestimating intake. The most common cause of "I'm not losing on 1,500 cal." Studies of food-frequency questionnaires vs measured intake show typical underreporting of 15 to 25%. Liquids (juice, coffee creamer, alcohol), tastes during cooking, and small snacks are the usual culprits.

2. Overestimating exercise burn. Cardio machines and fitness watches overestimate calorie burn by 20 to 50%. A "500 cal" elliptical session might be 350. Don't add full exercise calories back to your daily target.

3. Eating "diet" foods that aren't. Granola, smoothies, "healthy" wraps, salad with creamy dressings can deliver 500 to 800 cal per serving. The label says "low fat" or "natural" but the calorie density is high.

4. Skipping protein. Easy to do on a deficit. Eat the protein first at every meal. Aim for 25 to 40 g per meal across 3 to 4 meals.

5. Not lifting. Cardio alone in a deficit causes more muscle loss than resistance training plus cardio. Two to three resistance sessions per week is the floor for muscle preservation.

6. Dropping too fast. Going from 2,500 cal to 1,400 cal in a week causes a hunger crash and metabolic adaptation. Step down by 200 to 300 cal at a time over 2 to 4 weeks.

7. Weighing daily and obsessing over noise. Daily weight fluctuates by 2 to 4 lb from water, sodium, and bowel timing. Use 7-day rolling averages to see actual trend.

FAQ

How many calories should I eat to lose 1 pound a week? Eat about 500 calories per day below your maintenance level. For a 180 lb sedentary adult, maintenance is roughly 2,520 cal, so target around 2,000 cal/day. Adjust up or down based on actual weekly weight changes.

What is the lowest number of calories I should eat? The minimum recommended floor is 1,200 calories per day for women and 1,500 for men. Below these levels, micronutrient deficiencies and lean mass loss accelerate. Very-low-calorie diets at 800 calories require physician supervision.

How do I calculate my maintenance calories? Use bodyweight in pounds × 14 for sedentary, ×15 for light activity, ×16 for moderate, ×17 for very active. For more precision, use the Mifflin-St Jeor equation: men get RMR = (10 × kg) + (6.25 × cm) - (5 × age) + 5; women subtract 161 instead of adding 5.

Is 1,200 calories a day enough to lose weight? For most women, yes, but it's the floor, not the target for everyone. A 1,200 cal/day intake produces weight loss for anyone whose maintenance is above that, but it's hard to hit protein and micronutrient targets. Resistance training and protein priority matter most at this level.

How many calories to lose 2 pounds a week? A 1,000 calorie daily deficit. This is sustainable only for patients with higher maintenance (over 2,400 cal/day) and is hard to maintain past 8 to 12 weeks for most people. Slower loss is generally more durable.

Do I need to count calories every day? No, but you need a consistent strategy. Calorie counting is one tool; portion control plates, meal-template eating, and intuitive eating with a few rules can also work. Tracking for 2 to 4 weeks usually calibrates portion estimates well enough that ongoing tracking becomes optional.

Why am I not losing weight even on a calorie deficit? Most likely intake is higher than reported (under-tracking is common), exercise burn is lower than estimated, water and glycogen are masking fat loss in the first 2 to 3 weeks, or you're losing fat but gaining a small amount of muscle (best case). Re-track meticulously for 7 days to verify.

Does calorie quality matter or just quantity? Both matter. Quantity drives weight; quality (protein, fiber, micronutrients) drives body composition, energy, and adherence. Two diets at 1,800 cal can produce different results: high-protein, high-fiber preserves more muscle and feels less restrictive than low-protein, low-fiber.

How fast is too fast for weight loss? Sustained loss over 1.5% of body weight per week is too fast for most patients. For a 200 lb person, that's 3 lb/week. Beyond this rate, muscle loss, metabolic slowdown, and gallstone risk increase. The sweet spot is 0.5 to 1% per week.

Should I eat back calories from exercise? Partially. Fitness trackers overestimate burn by 20 to 50%. A reasonable rule: eat back about 50% of estimated exercise calories on training days. This keeps you in deficit without under-fueling workouts.

Can I lose weight without counting calories? Yes, by using portion-control strategies that approximate a deficit. The plate method (half vegetables, quarter protein, quarter starch), eating only at meals (no grazing), avoiding liquid calories, and prioritizing protein at each meal can produce a 300 to 500 cal/day deficit without explicit tracking.

Does intermittent fasting lower the calorie target? No. Intermittent fasting is a meal-timing strategy, not a calorie strategy. The same deficit produces the same weight loss whether eaten in 8 hours or 16. Choose the schedule that's most sustainable for you.

How do GLP-1 medications change my calorie target? They reduce appetite, so most patients spontaneously eat 20 to 30% below maintenance. You may not need to count obsessively, but you do need to hit protein (0.7 to 1.0 g/lb) and stay above the calorie floor (1,200/1,500). Discuss specifics with your provider.

Will my metabolism slow down if I eat too little? Yes, partially. Below an aggressive deficit (over 25% below TDEE for more than 4 to 6 weeks), resting metabolic rate drops by 5 to 15% beyond what mass loss alone would predict. This is reversible with a "diet break" of 1 to 2 weeks at maintenance every 8 to 12 weeks of cutting.

Author / review note

Reviewed by the FormBlends Medical Team. References include Mifflin et al. (American Journal of Clinical Nutrition, 1990) on resting metabolic rate prediction, Hall et al. (Lancet, 2011) on dynamic body weight modeling, the Academy of Nutrition and Dietetics adult weight management guidelines 2020, the SURMOUNT-1 trial (Jastreboff et al., NEJM, 2022), and Helms et al. (IJSNEM, 2017) on protein during energy restriction.

Related reading on FormBlends:

• /articles/food-and-diet/protein-on-glp-1/
• /articles/food-and-diet/calorie-deficit-glp-1/
• /articles/exercise-fitness/resistance-training-deficit/

Sources

1. Mifflin et al. (American Journal of Clinical Nutrition, 1990) on resting metabolic rate prediction.
2. Hall et al. (Lancet, 2011) on dynamic body weight modeling.
3. The Academy of Nutrition and Dietetics adult weight management guidelines 2020.
4. The SURMOUNT-1 trial (Jastreboff et al., NEJM, 2022).
5. Helms et al. (IJSNEM, 2017) on protein during energy restriction.

Footer disclaimers (all 4 verbatim)

Platform Disclaimer. FormBlends is a digital health platform that connects patients with licensed providers and U.S.-based pharmacies. We do not manufacture, prescribe, or dispense medication directly. All clinical decisions are made by independent licensed providers.

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