How to use the weight loss calculator
- Pick your Weight units, pounds or kilograms.
- Enter your Current weight and Goal weight.
- Choose Plan by Target date to enter a deadline, or Weekly loss to enter how much you want to lose each week and get a finish date.
- Enter your Maintenance calories (TDEE) per day, the calories you burn at your current weight. If you do not know it, estimate it with the Calorie and TDEE Calculator.
- Read Loss per week, Daily deficit and Eat per day, plus any warnings underneath.
How the calculation works
The calculator uses the long-standing rule of thumb that a pound of body fat holds about 3,500 calories (Wishnofsky, 1958), or about 7,716 per kilogram. The NHLBI practical guide ties a 500 to 1,000 calorie daily deficit to losing 1 to 2 pounds a week.
Daily deficit = (current weight minus goal weight) × 3,500 ÷ days
Loss per week = (current weight minus goal weight) ÷ (days ÷ 7)
Eat per day = maintenance calories minus daily deficit
In Weekly loss mode the deficit is the weekly rate × 3,500 ÷ 7, and the days are pounds to lose ÷ weekly rate × 7.
Worked example
The page opens with 180 lb now, a 160 lb goal, a Target date 90 days from today and maintenance calories of 2,400. That is 20 lb to lose: 20 × 3,500 = 70,000 calories, spread over 90 days is 778 a day. Loss per week is 20 ÷ (90 ÷ 7) = 1.56 lb. Eating 2,400 minus 778 gives 1,622 kcal a day, the three numbers the tiles show.
Limits and edge cases
- The 3,500 rule is a straight-line average. As you get lighter your maintenance calories fall, so real loss slows (Hall et al., Lancet 2011). The NIDDK Body Weight Planner models that slowdown. Re-run this calculator every few weeks with your new weight.
- You get a warning above 2 lb (0.9 kg) per week, and another when calories to eat fall below 1,200 a day. NHLBI plans start at 1,000 to 1,200 for most women and 1,200 to 1,600 for men.
- If the deficit is as large as your maintenance calories, the plan is marked not possible.
- Without height, age or sex it cannot judge whether a goal weight is healthy. Check with the BMI Calculator and the Ideal Weight Calculator.
- It is not for anyone under 18, pregnant, or with a medical condition or eating disorder history. Ask a clinician first.
Exercise counts toward the deficit too. Estimate it with the Calories Burned Calculator.
Frequently asked questions
How many calories should I cut to lose 1 pound a week?
About 500 per day, because 500 × 7 = 3,500 calories, the usual estimate for a pound of body fat. Two pounds a week needs about 1,000 a day.
How fast can I safely lose weight?
The CDC says a gradual, steady pace of about 1 to 2 pounds a week is more likely to keep the weight off. The calculator warns you when a plan needs more than 2 pounds a week.
Why am I losing weight slower than the calculator says?
The 3,500 calorie rule is a straight-line average. As you lose weight your maintenance calories drop, so the same intake produces less loss. Recalculate every few weeks with your new weight.
How do I find my TDEE?
TDEE is the calories you burn in a day, including activity. Estimate it from your age, height, weight and activity level, or average what you eat over two or three weeks of steady weight.
Does this weight loss calculator work in kilograms?
Yes. Switch Weight units to kilograms and every weight and weekly rate converts. The math then uses about 7,716 calories per kilogram of body fat.
Sources: CDC, Steps for Losing Weight; NHLBI, The Practical Guide; Wishnofsky, Am J Clin Nutr 1958; Hall et al., Lancet 2011.
Disclaimer: General estimates, not medical advice. Check with a healthcare provider before starting a weight loss plan.