Find out exactly how many calories you need to eat to reach your goal weight, and how long it will take to get there.
This calculator is for informational purposes only and not a substitute for medical advice. Individual needs vary. Consult a healthcare provider before making changes. Eating fewer than 1,200 (women) or 1,500 (men) calories a day is not recommended.
A pound of body fat stores roughly 3,500 kcal, so a 500 kcal/day deficit averages ~1 lb/week of weight loss. Sustainable deficits range 15-25% below TDEE. Going deeper than 25% accelerates muscle loss, hormonal disruption, and rebound. GLP-1 drugs achieve a deficit by suppressing appetite, patients average 25-30% reductions without willpower.
Source: Wishnofsky M. Am J Clin Nutr 1958 · STEP / SURMOUNT trial dataA calorie deficit is what happens when you consistently eat fewer calories than your body burns each day. It's the single non-negotiable requirement for fat loss, the law of thermodynamics applies to human bodies the same way it applies to everything else in the universe. Every diet that has ever worked for weight loss, regardless of what it called itself, created a calorie deficit. That's true whether the label was low-carb, low-fat, keto, intermittent fasting, carnivore, paleo, Mediterranean, or Weight Watchers.
The size of the deficit matters as much as its existence. A small, sustainable deficit preserves muscle, supports hormones, and produces fat loss that actually sticks. An aggressive deficit causes rapid scale-weight drop, and costs you muscle, thyroid function, sleep, libido, and your long-term relationship with food.
When your body takes in less energy than it uses, it has to get the missing energy somewhere. The primary sources are:
The goal of a well-structured deficit is to ensure that the weight you lose comes overwhelmingly from fat, not muscle. The three levers that control this are:
Bottom line: The scale number is only useful when combined with waist measurement, progress photos, strength numbers, and how your clothes fit. Fat loss and weight loss are not the same thing.
"Eat less" is terrible advice without a specific number. And the right number depends on how much fat you have to lose, how much muscle you want to keep, and how much time you're willing to spend.
This is the default for most people. Produces ~0.5-1% of bodyweight loss per week. Preserves muscle, allows hard training, and is sustainable for 12-20 weeks at a time. This is what we recommend as a starting point.
Appropriate for people with significant fat to lose (BMI 30+) or short timelines. Requires high protein intake, resistance training, and often a structured refeed strategy. Not ideal for lean individuals trying to get leaner, losses will come disproportionately from muscle.
Used for recomposition, late-stage body composition work, or people with history of dieting burnout. Slower but sustainable for much longer. Combined with resistance training, can produce meaningful body composition change without feeling like "a diet."
| Deficit Level | Weekly loss | Best for |
|---|---|---|
| 5-10% | 0.25-0.5 lb | Lean individuals, recomposition, long-term phases |
| 10-20% | 0.5-1.5 lb | Most people. Best balance of speed, muscle retention, and sustainability |
| 20-30% | 1.5-2.5 lb | BMI 30+, short-term phases, closely supervised |
| 30%+ | 2.5+ lb | Medical or surgical contexts only. Not recommended for general fat loss. |
The absolute floor most guidelines agree on: don't eat below 1,200 calories/day (women) or 1,500 calories/day (men) without medical supervision. Very low calorie diets (below these floors) exist for specific clinical situations but require provider oversight.
A 500-calorie deficit can come from cutting food, burning more through movement, or a combination. The research is clear on which works better:
It's much easier to cut 500 calories from your plate than to burn 500 calories through exercise. A Snickers bar is 280 calories, eaten in two minutes. Burning 280 calories requires 30-40 minutes of moderate running for most people.
As a general ratio: aim for 70-80% of your deficit from diet and 20-30% from increased activity. Exercise earns you less calorie wiggle room than most people think, and wearables overestimate calorie burns by 20-30% or more.
Exercise isn't about burning calories, it's about keeping the deficit healthy. Specifically:
The honest ratio: 90% of successful fat loss comes from diet. 100% of successful body recomposition comes from training. You need both.
500 calories feels slow. 1,000 calories feels fast. But the fast deficit costs you muscle, sleep, mood, libido, and hunger regulation. Start moderate.
Research shows people consistently underreport calories by 20-40%. Weekend meals, drinks, bites, cooking oil, and "handfuls of" everything add up. Weigh and track honestly.
Low-protein deficits lose more muscle per pound than high-protein deficits. Minimum: 0.7-1.0 g protein per pound of goal bodyweight.
Without resistance work, up to 25% of your weight loss can come from muscle. With strength training, that drops to under 5%.
Apple Watches, Fitbits, and Garmins regularly overestimate calorie burn by 20-30%. Don't "eat back" calories from wearables.
As you lose weight, TDEE drops. A 25-lb loss can lower maintenance by 150-250 calories. Recalculate deficit every 10-15 lbs.
Every long deficit eventually stalls. There are three common causes:
The most common cause of a plateau, by far, is calorie creep. Portions drift, tracking loosens, weekends get generous. Re-weigh everything for a week. 80% of plateaus solve themselves.
Your body's legitimate response to prolonged caloric restriction: BMR drops slightly, NEAT drops (you fidget less, move less, feel colder), and hunger hormones increase. This is normal and predictable. In a 12-week deficit, expect TDEE to drop 5-15% beyond what calculators predict.
Solutions: diet breaks (1-2 weeks at maintenance every 8-12 weeks) or refeeds (1-2 high-carb days per week) can partially reverse adaptation. They also make adherence much easier.
Sometimes the scale doesn't move but the waist is shrinking. Strength workouts add retained water and glycogen to muscle. Measure progress with photos, waist circumference, and the way clothes fit, not just the number on the scale.
When to break: If you've been in a deficit for 12+ weeks with no progress, consider 10-14 days at maintenance calories. It resets hormones, restores NEAT, and usually kickstarts renewed loss when you reintroduce the deficit.
For most people, yes, 500 calories below TDEE produces about 1 lb/week of fat loss, which is sustainable and muscle-sparing. If you have more weight to lose or want faster results, 750-1,000 can work short-term with good protein intake and strength training. If you're already lean, 300-500 is often more appropriate.
The most likely answer: you're not actually in as big a deficit as you think. People consistently under-report calorie intake by 20-40%. Other common causes include water retention (from salt, training, or hormone cycles), metabolic adaptation, undetected medical issues (thyroid, PCOS), and insufficient sleep. Re-weigh food for a week and track everything before changing the plan.
0.5-1% of bodyweight per week is the sweet spot for most people. Faster is possible but usually costs muscle and is harder to sustain. For a 200-lb person, that's 1-2 lbs per week. For a 130-lb person, it's 0.5-1 lb per week.
Yes, but with caveats. "Body recomposition" (simultaneous fat loss and muscle gain) works best for: beginners, people returning after a break, people with higher body fat, and people using a small deficit. Advanced, lean lifters usually have to alternate between surplus (gaining) and deficit (cutting) phases. High protein intake and progressive resistance training are non-negotiable either way.
For the deficit itself, yes, a calorie is a calorie. But the source affects body composition, satiety, and training performance. High-protein deficits preserve more muscle. Higher-carb days typically mean better workouts. Higher-fat days tend to feel more satisfying for some people. Start with protein target first, then distribute remaining calories based on preference.
GLP-1s don't change the physics, you still need a calorie deficit to lose fat. What they change is how easy it is to create one. They reduce hunger and slow digestion, making a 500-1,000 calorie deficit feel nearly effortless. The risk: significant muscle loss if protein isn't prioritized. Anyone on GLP-1s should aim for 1.0+ g of protein per pound of goal bodyweight and resistance train. See our GLP-1 article for details.
No, research comparing IF to other deficit strategies shows equivalent fat loss at equal calorie intake. IF is a tool that some people find makes hitting a calorie target easier. Others eat more during their window and end up even. Use it if it fits your life; skip it if it doesn't.
Generally, no, at least not all of them. Fitness trackers overestimate calorie burn by 20-30%. If you calculated your deficit based on your TDEE activity level, exercise is already included. If you want to eat slightly more on hard training days, add 100-200 calories rather than the full "burn" the watch reports.
Yes, aggressive deficits, especially in lean individuals, can suppress thyroid, testosterone, estrogen, and leptin. This is why modest deficits and periodic maintenance breaks matter. If you're experiencing fatigue, low libido, menstrual disruption, or cold intolerance during a deficit, the deficit is too aggressive. Restore calories to maintenance and consider hormone testing.
A deficit number is only useful if everything else lines up. These tools cover the rest of the system, protein, body comp, hormones, and the metabolic baseline you're cutting from.
Hand-picked guides on cutting strategy, plateaus, muscle preservation, and the pharmacological levers that work when willpower stalls.
GLP-1 receptor agonists suppress hunger, slow gastric emptying, and quiet food noise, which allows a sustained calorie deficit without willpower. In trials of FDA-approved branded preparations: tirzepatide (SURMOUNT-1) avg 20.9% body-weight reduction at 72 weeks; semaglutide (STEP-1) avg 14.9% at 68 weeks. Compounded preparations are not FDA-approved.
How this tool calculates
Calorie deficit estimates are based on thermodynamic principles: a sustained 3,500-calorie weekly deficit produces approximately 1 lb of body weight loss, with adjustments for metabolic adaptation per Hall et al. models. Actual outcomes vary with body composition, training, and hormonal factors.
Peer-reviewed sources
Important. This tool is provided for educational purposes only and does not constitute medical advice, diagnosis, or treatment. The tool does not prescribe medication, recommend specific dosing, or substitute for clinical evaluation. Compounded medications referenced anywhere on this site are not FDA-approved; the FDA does not verify the safety, effectiveness, or quality of compounded drugs. Treatment decisions are made only by a licensed U.S. physician after individual patient evaluation.