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Calorie deficit calculator: a realistic timeline

Short answer

The popular rule says 3,500 kcal equals a pound (about 7,716 kcal per kg), so a 500 kcal daily deficit would take 10 kg off in about 23 weeks. Research shows that overestimates: as you lose weight you burn less, so a 500 kcal cut eventually levels off at about 21 kg lost, with roughly half of that in the first year.

Last reviewed 27 October 20263 published sourcesNot medical advice

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Calorie deficit calculator

Compare the popular 3,500-calorie rule with what a research model expects once your body adapts.

Enter your current weight, goal weight and daily calorie deficit.

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Two ways to forecast

Wishnofsky's 1958 estimate of about 3,500 kcal per pound of body weight (Wishnofsky, 1958) gave us the rule that a fixed deficit removes weight at a fixed rate. Thomas et al. showed it grossly overestimates weight loss beyond the short term (Thomas et al., 2013).

Hall et al. modelled how energy expenditure adapts. For an average overweight adult, every 100 kJ (about 24 kcal) a day change in intake leads to an eventual body weight change of about 1 kg, with half of it in about a year and 95% in about three years (Hall et al., 2011). The calculator shows both forecasts.

What a lasting daily deficit leads to
Daily deficit	Rule: weeks per 5 kg	Eventual loss (Hall)	After 1 year
250 kcal	22.0	10.5 kg	5.2 kg
500 kcal	11.0	20.9 kg	10.5 kg
750 kcal	7.3	31.4 kg	15.7 kg
1,000 kcal	5.5	41.8 kg	20.9 kg

Rule: 5 kg × 7,716 kcal ÷ deficit ÷ 7. Hall: deficit × 4.184 ÷ 100 kJ per kg, with half reached in about a year. Hall's figures are averages for overweight adults.

Setting the deficit

Your deficit is your maintenance calories minus what you eat. Estimate maintenance with the TDEE calculator, keep protein up with the protein calculator, and see what extra activity adds with the calories burned calculator.

Keep the deficit honest

Reps logs meals by photo, voice or text with a full macro breakdown, so the deficit you plan is the one you actually eat.

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Common questions

Is the 3,500-calorie rule wrong?

As a long-term forecast, yes. Thomas et al. compared it with seven tightly controlled weight-loss experiments and concluded it grossly overestimates actual weight loss, because energy expenditure falls as weight comes off.

How much weight will a 500-calorie deficit lose?

By the 3,500-calorie rule, about 0.45 kg (1 lb) a week indefinitely. In Hall et al.'s model for an average overweight adult, a lasting 500 kcal daily cut leads to an eventual loss of about 21 kg, reached slowly: about half in a year and 95% in about three years.

Why does weight loss slow down?

A smaller body needs less energy to run and to move, so the same intake becomes a smaller deficit. Hall et al. found the body weight response to a change in intake is slow, with a half time of about a year, and that people with more body fat take longer to reach their new steady weight.

Sources

Figures on this page were checked against these publications on 27 October 2026.

Wishnofsky M. Caloric equivalents of gained or lost weight. American Journal of Clinical Nutrition. 1958;6(5):542–546. doi.org/10.1093/ajcn/6.5.542
Thomas DM, Martin CK, Lettieri S, Bredlau C, Kaiser K, Church T, Bouchard C, Heymsfield SB. Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule. International Journal of Obesity. 2013;37(12):1611–1613. doi.org/10.1038/ijo.2013.51
Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA. Quantification of the effect of energy imbalance on bodyweight. The Lancet. 2011;378(9793):826–837. doi.org/10.1016/S0140-6736(11)60812-X

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