Weight Loss Calculator

Estimate how long it will take to reach your goal weight based on your age, sex, activity level, and chosen calorie deficit. Uses the Mifflin-St Jeor BMR equation with evidence-based loss rate recommendations from the CDC and NIH.

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Your Information

Age

Sex

Height

Feet + inches

Current Weight (lbs)

Goal Weight (lbs)

Activity Level

Loss Rate

Weight Loss Timeline

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Weeks to Goal

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Goal Date

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Total Weight to Lose

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Your BMR

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Your TDEE

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Daily Calorie Target

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Daily Deficit

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The Science of Weight Loss

Weight loss fundamentally requires a calorie deficit — burning more calories than you consume. The widely cited "3,500 calories = 1 pound" rule (from a 1958 paper by Max Wishnofsky) provides a useful approximation: a deficit of 500 calories/day leads to roughly 1 pound of loss per week. However, a 2011 model published in The Lancet by Kevin Hall et al. showed that the actual relationship is dynamic — as you lose weight, your BMR decreases, requiring ongoing adjustments to maintain the same deficit.

The National Institutes of Health (NIH) and CDC both recommend a loss rate of 1-2 pounds per week as safe and sustainable. Faster rates increase muscle loss risk, metabolic adaptation, gallstone risk, and are associated with higher regain rates. A 2016 meta-analysis in Obesity Reviews found that gradual weight loss led to greater long-term maintenance than rapid approaches, with 80% of rapid losers regaining within 5 years.

Safe Weight Loss Rates

Rate	Daily Deficit	Monthly Loss	Sustainability	Best For
0.5 lb/week	250 cal	~2 lbs	Excellent	Last 10-15 lbs, maintenance transition
1 lb/week	500 cal	~4 lbs	Very Good	Most people — recommended by CDC/NIH
1.5 lb/week	750 cal	~6 lbs	Moderate	Higher starting weight (BMI 30+)
2 lb/week	1,000 cal	~8 lbs	Challenging	Medical supervision recommended

Never consume below 1,200 cal/day (women) or 1,500 cal/day (men) without medical supervision. Sources: CDC Healthy Weight guidelines, NIH NIDDK.

Common Weight Loss Plateaus — What Research Says

Plateaus typically occur at 6-8 weeks and 6 months into a weight loss program. A 2014 study in the American Journal of Clinical Nutrition found that metabolic adaptation reduces BMR by approximately 15% beyond what weight loss alone would predict — the body actively resists further loss through reduced non-exercise activity thermogenesis (NEAT) and hormonal changes (increased ghrelin, decreased leptin).

Breaking plateaus requires either increasing activity, reducing intake by 100-200 additional calories, or incorporating diet breaks (1-2 weeks at maintenance calories). A 2018 study in the International Journal of Obesity found intermittent dieting (2 weeks deficit, 2 weeks maintenance) produced 50% greater fat loss than continuous dieting over the same period.

For precise calorie targets, use our Calorie Calculator and TDEE Calculator. Track body composition with the Body Fat Calculator and BMI Calculator. Find your optimal macro split with the Macro Calculator.

Frequently Asked Questions

How much weight can I safely lose per week?

The CDC and NIH recommend 1-2 pounds per week as the safe range. This requires a daily calorie deficit of 500-1,000 calories. Losing faster than 2 lbs/week increases muscle loss, gallstone risk, and nutrient deficiency risk. People with higher starting weights (BMI 30+) may safely lose faster initially.

How many calories should I eat to lose weight?

Start by calculating your TDEE (Total Daily Energy Expenditure), then subtract your deficit. For 1 lb/week loss, subtract 500 calories from TDEE. Never go below 1,200 cal/day (women) or 1,500 cal/day (men) without medical guidance. Use our Calorie Calculator for a personalized target.

Why has my weight loss stalled?

Plateaus are normal and typically occur at 6-8 weeks. As you lose weight, your BMR decreases, reducing your TDEE and shrinking your deficit. Solutions: recalculate your calories at your new weight, increase activity by 100-200 calories, add a 1-2 week diet break at maintenance, or adjust your macro ratio.

Is it better to eat less or exercise more?

Both work, but dietary changes are more efficient for creating a calorie deficit. Running 3 miles burns ~300 calories (30-40 minutes of effort), while skipping a large muffin saves ~400 calories (zero time). The optimal approach combines moderate calorie reduction (300-500 cal) with regular exercise (150+ minutes/week) for both weight loss and health benefits.

Does metabolism slow down when you diet?

Yes. Metabolic adaptation (also called adaptive thermogenesis) reduces BMR by about 15% beyond what weight loss alone explains. This is an evolutionary survival mechanism. To minimize it: maintain adequate protein intake (0.7-1g per pound of body weight), include resistance training, avoid very low calorie diets, and consider periodic diet breaks.

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