Calorie Deficit Calculator

To lose weight, you need to eat fewer calories than your body burns — and this calorie deficit calculator tells you exactly how many fewer. It estimates your maintenance calories using the Mifflin-St Jeor equation, then produces a daily calorie target for weight loss based on your chosen rate of loss. The widely cited 3,500-calorie rule — that a 3,500-calorie deficit produces approximately one pound of fat loss — is the basis for this calculation. A 500-calorie daily deficit produces roughly 1 pound of loss per week; a 250-calorie deficit produces roughly 0.5 pounds per week. This calorie deficit calculator also shows how long it would take to reach a goal weight if you provide one, giving you a concrete timeline rather than an open-ended restriction. Supports both imperial and metric inputs.

How to Use the Calorie Deficit Calculator

• Select your sex and enter your age.
• Choose your height unit and enter your height.
• Choose your weight unit and enter your current weight.
• Select your activity level — this determines your maintenance calorie baseline.
• Select your weekly loss goal from the dropdown — 0.5 lbs/week for a mild sustainable cut, 1 lb/week for the standard recommendation, or 1.5–2 lbs/week for a more aggressive approach.
• Optionally enter a goal weight (in the same unit as your current weight) to see a projected timeline.
• Click "Calculate My Deficit" to see your target, deficit, expected loss rate, and timeline.

Worked Example: 160 lbs to 140 lbs

A 28-year-old female, 160 lbs (72.6 kg), 5'6" (167.6 cm), moderately active, targeting a standard 1 lb/week loss:

• BMR: (10 × 72.6) + (6.25 × 167.6) − (5 × 28) − 161 = 1,473 cal/day
• Maintenance (×1.55): 1,473 × 1.55 = 2,283 cal/day
• Daily calorie target (−500 deficit): 1,783 cal/day
• Expected loss: ~1 lb/week
• Timeline to 140 lbs: ~20 weeks (~5 months)

At 1.5 lbs/week instead (daily target: 1,533 calories), the same 20-pound goal takes about 13 weeks — but with a tighter daily budget and higher risk of muscle loss without adequate protein.

When Would You Use This?

Starting a structured calorie deficit for weight loss. Rather than picking an arbitrary calorie number, this calorie deficit calculator gives you a daily target calibrated to your body size, activity level, and chosen rate of loss — reducing guesswork and giving you a concrete number to work toward each day.

Planning for a deadline. If you have a specific event — a wedding, a competition, a vacation — and need to reach a goal weight by a certain date, the timeline estimate helps you work backward and choose a rate of loss that is achievable without extreme restriction.

Auditing your current intake. Enter your stats and see what a healthy deficit looks like for you. If you have been restricting calories but not losing weight, your actual intake may be higher than you think — this calculator shows what the real numbers should be for your body.

Frequently Asked Questions

What is a calorie deficit?

A calorie deficit occurs when you consume fewer calories than your body burns in a day. When your intake is lower than your total daily energy expenditure (TDEE), your body draws on stored fat and glycogen for fuel, which results in weight loss over time. The size of the deficit determines the rate of loss — a larger deficit produces faster weight loss but can also cause muscle loss, fatigue, and metabolic adaptation if maintained too aggressively.

How big should my calorie deficit be?

Most nutrition and fitness guidelines recommend a deficit of 250–500 calories per day for sustainable fat loss. A 250-calorie daily deficit produces roughly 0.5 pounds of loss per week; a 500-calorie deficit produces roughly 1 pound per week. These rates preserve muscle mass and are realistic to maintain for weeks or months. Deficits of 750–1,000 calories per day can produce faster results but carry higher risk of muscle loss, poor recovery, low energy, and are difficult to sustain.

What is the 3,500-calorie rule?

The 3,500-calorie rule states that burning or cutting 3,500 more calories than you consume results in approximately one pound of fat loss. This produces the simple equation used in this calculator: a 500-calorie daily deficit × 7 days = 3,500 calories = 1 pound per week. The rule is a practical approximation — actual results vary due to water retention, muscle changes, and metabolic adaptation, particularly over longer timeframes. It remains the most widely used tool for setting weight loss calorie targets.

Is a 500-calorie deficit safe?

For most healthy adults, a 500-calorie daily deficit — producing roughly 1 pound of loss per week — is widely considered safe and sustainable. This calculator enforces a minimum calorie floor of 1,500 calories per day for men and 1,200 calories per day for women regardless of the deficit size selected. Eating below these thresholds is associated with muscle loss, nutritional deficiencies, and metabolic slowdown, and the calculator will adjust your target upward to these floors if needed.

How long does it take to lose 10 or 20 pounds?

At a standard 500-calorie daily deficit — producing roughly 1 pound of loss per week — losing 10 pounds takes approximately 10 weeks (about 2.5 months) and losing 20 pounds takes approximately 20 weeks (about 5 months). At a mild 250-calorie deficit, those same goals take 20 and 40 weeks respectively. Enter a goal weight in the calculator above to get a personalized timeline based on your specific stats, activity level, and chosen rate of loss.

What happens if my calorie deficit is too large?

Deficits larger than 1,000 calories per day for most people can lead to significant muscle loss, hormonal disruption, fatigue, nutrient deficiencies, and a reduced metabolic rate — meaning your body adapts to burn fewer calories over time, making further progress harder. For long-term fat loss, a moderate and consistent deficit paired with adequate protein intake is more effective than aggressive restriction. If you experience persistent energy loss, declining strength, or stalled weight loss, your deficit is likely too large.