Is the 3,500-kcal-per-pound rule accurate?

It's a widely used approximation, but peer-reviewed research shows it overestimates real weight loss over time because it doesn't account for metabolic adaptation — actual loss typically slows as you lose weight, unlike this simple linear projection.

What's a safe rate of weight loss?

The CDC recommends 0.5-2 lb/week for sustainable, muscle-sparing weight loss. Faster rates increase the risk of losing muscle mass along with fat and are generally harder to maintain.

Why does the calculator warn me about very low calorie targets?

Sustained intake below roughly 1,500 kcal/day for men or 1,200 for women risks nutrient deficiencies and typically calls for medical supervision — the warning suggests a slower rate or lower activity assumption instead.

Does this account for changing metabolism as I lose weight?

No — it's a static, linear projection. Real metabolic adaptation means your maintenance calories (and therefore your actual deficit at a fixed intake) change as your weight changes, which is why 'estimated time to goal' should be treated as a rough estimate.

Should I eat back calories burned from exercise?

This calculator's activity multiplier already accounts for your general activity level in the TDEE estimate — deliberately eating back additional exercise calories on top of that can undermine the deficit you're targeting.

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Health & Fitness

Calorie Deficit Calculator

Daily calorie target and estimated time to your goal weight, at a safe deficit rate.

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Last reviewed 2026-08-30

About the Calorie Deficit Calculator

Calculates the daily calorie target needed to lose weight at a chosen rate, using the Mifflin-St Jeor formula for maintenance calories (the same one used across this site's calorie/TDEE tools) and the traditional 3,500-kcal-per-pound rule for the deficit itself, with an optional estimated time to a goal weight.

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How to use it

Enter your sex, age, height, and current weight.
Choose your activity level.
Choose a target weight-loss rate — the CDC's recommended safe range is 0.5-2 lb/week.
Optionally enter a goal weight to see an estimated time to reach it.
Read your target daily calories and daily deficit needed.

Formula

BMR (Mifflin-St Jeor) = 10×weight(kg) + 6.25×height(cm) − 5×age + 5 (men) or −161 (women). TDEE (maintenance) = BMR × activity multiplier. Daily deficit needed = (target weekly loss rate in lb × 3,500 kcal) ÷ 7. Target daily calories = TDEE − daily deficit. Estimated weeks to goal = (current weight − goal weight, in lb) ÷ target weekly rate.

Worked example

A 30-year-old male, 175cm, 72kg, moderately active (TDEE ≈ 2,627 kcal), targeting 1 lb/week loss: daily deficit of 500 kcal, for a target of about 2,127 kcal/day.

Safe Weight-Loss Guidelines

Safe Weight-Loss Guidelines
Guideline	Value
CDC recommended weekly loss rate	0.5-2 lb/week
Commonly recommended calorie floor — men	1,500 kcal/day
Commonly recommended calorie floor — women	1,200 kcal/day

Interpreting your result

The 3,500-kcal-per-pound rule is a traditional approximation traceable to a 1958 estimate (Wishnofsky). Peer-reviewed research (Hall & Chow, 2013, International Journal of Obesity) shows this static rule overestimates real-world weight loss because it ignores metabolic adaptation — as body weight drops, maintenance calorie needs drop too, so actual loss typically slows compared to this simple linear projection, especially over several months. Treat 'estimated time to goal' as a rough starting estimate, not a guarantee — the NIH Body Weight Planner is the standard reference for a more sophisticated individualized projection. This tool also flags targets below a commonly recommended calorie floor (1,500 kcal/day for men, 1,200 for women) and rates exceeding the CDC's 2 lb/week safe maximum.

Recommendations

• The CDC's recommended safe weight-loss range is 0.5-2 lb/week — faster rates are more likely to cost muscle mass along with fat and are harder to sustain long-term.
• Real-world weight loss typically slows over time compared to this linear projection, since maintenance calorie needs drop as body weight drops (metabolic adaptation) — don't be discouraged if progress isn't perfectly linear.
• If your target falls below the commonly recommended calorie floor (1,500 kcal/day for men, 1,200 for women), consider a slower rate or medical supervision instead of sustained very-low-calorie eating.

Frequently asked questions

So the maintenance-calorie baseline matches exactly across all three tools — the deficit math here is layered on top of the same Mifflin-St Jeor TDEE calculation.