Calorie Deficit Calculator
Find exactly how many calories to eat to lose weight at the pace you want. Choose a mild, moderate, or aggressive deficit based on your TDEE — and see how long it takes to hit your goal.
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How This Calorie Deficit Calculator Works
This calculator uses a two-step process. First it calculates your TDEE (Total Daily Energy Expenditure) using the Mifflin-St Jeor equation — the most accurate BMR formula for the general population — multiplied by your activity factor. Then it subtracts three standard deficit amounts to give you mild, moderate, and aggressive daily calorie targets.
All three targets are automatically floored at your BMR — the minimum calories your body needs for basic survival functions. Going below BMR consistently leads to muscle loss, hormonal disruption, and metabolic slowdown.
Choosing the Right Deficit Level
The right deficit depends on how much body fat you have to lose, how important performance is to you, and how strictly you can track calories.
- Mild deficit (−250 kcal/day, ~0.5 lb/week)
Best for people close to their goal weight, those with high training volume who need to support performance, or anyone who struggles with strict restriction. The smaller deficit means more margin for error in tracking.
- Moderate deficit (−500 kcal/day, ~1 lb/week)
The most researched and recommended deficit for most people. Produces meaningful results while being sustainable for months. The majority of controlled weight-loss studies use this exact deficit.
- Aggressive deficit (−750 kcal/day, ~1.5 lb/week)
Appropriate for people with significant weight to lose or those on a time-limited cut. Requires rigorous protein intake (1.8–2.4g/kg) and resistance training to minimize muscle loss. Harder to sustain beyond 8–12 weeks.
Why the Scale Lies (And What to Do Instead)
Body weight fluctuates by 1–5 lbs daily due to water retention, glycogen levels, digestive content, and hormonal cycles. If you weigh yourself after a salty meal or a hard training session, you may appear to have gained weight despite being in a calorie deficit.
The fix: weigh yourself daily at the same time (morning, after bathroom, before eating), then look at the 7-day average. A downward trending average over 2–3 weeks confirms your deficit is working — regardless of day-to-day noise.
Frequently Asked Questions
What is a calorie deficit?
A calorie deficit occurs when you consume fewer calories than your body burns (your TDEE). This forces your body to use stored energy — primarily body fat — to make up the difference, resulting in weight loss. A deficit of 3,500 calories roughly equals one pound of fat loss.
How large should my calorie deficit be?
Most research supports a moderate deficit of 500 kcal/day (roughly 1 lb/week) as the sweet spot between results and sustainability. Mild deficits (250 kcal/day) are easier to maintain and cause less muscle loss. Aggressive deficits (750+ kcal/day) produce faster weight loss but increase the risk of muscle loss and are harder to sustain.
Can I go below my BMR to lose weight faster?
No. Eating below your BMR — the calories your body needs just for vital functions — significantly increases muscle loss, slows your metabolism over time, and can cause nutrient deficiencies. Your calorie intake should always remain above your BMR, which this calculator enforces automatically.
Why am I not losing weight in a deficit?
The most common reason is calorie tracking inaccuracy — research shows people underestimate food intake by 20–50%. Other factors include metabolic adaptation (TDEE decreasing over time as you lose weight), water retention masking fat loss on the scale, and overestimating activity level. Weigh yourself weekly at the same time for more accurate data.
How do I maintain muscle while losing weight?
The two key levers are high protein intake (1.8–2.4g per kg of body weight) and resistance training. A calorie deficit creates a catabolic environment, but sufficient protein and progressive overload training signal your body to preserve muscle tissue. This is why protein targets are higher during a cut than during maintenance.
Does the calorie deficit need to be the same every day?
No. What matters is the weekly deficit total, not the daily breakdown. Many people use calorie cycling — eating at maintenance or a small surplus on training days and a larger deficit on rest days — to support performance while still losing fat. As long as the weekly total creates the right deficit, fat loss occurs at the same rate.