Weight Loss Date Calculator

A goal weight date is the day the scale should reach the number you picked. To get it, any weight loss date calculator needs two things: how much you want to lose and how fast you will lose it. This one lets you set the speed as a daily calorie deficit or a weekly pace, or work backward from a target date.

It also shows two answers instead of one. The first is the classic 3,500 calorie rule that most calculators use. The second lets your energy needs fall as your weight falls, which is what happens in a real body, so it lands later. The gap between the two is the most useful thing on this page.

How to calculate your goal weight date

Every goal weight date starts with the same number: current weight minus goal weight. The two methods differ in how they turn a daily calorie deficit into pounds.

1. The 3,500 calorie rule. Weeks to goal = pounds to lose × 3,500 ÷ (daily deficit × 7). In metric, use 7,700 calories per kilogram. For 30 lb at 500 calories a day: 30 × 3,500 ÷ 3,500 = 30 weeks. The rule assumes the deficit stays the same size from the first day to the last.
2. The falling-needs estimate. A smaller body burns less energy: about 24 calories a day less for every kilogram lost, or 10.8 for every pound. That is the 100 kJ per kilogram rule of thumb from Hall et al. (2011) in The Lancet, which they round to 10 calories per pound. If you keep eating the same amount, your deficit shrinks as you lose. Days to goal = −323 × ln(1 − pounds to lose × 10.84 ÷ daily deficit). For the same example: 30 × 10.84 ÷ 500 = 0.65, the natural log of 0.35 is −1.05, and 323 × 1.05 = 339 days, or 48.5 weeks.

The 323 in that formula is 3,500 divided by 10.84. It sets how quickly the deficit fades. When pounds to lose × 10.84 is larger than your daily deficit, the formula has no answer, because your weight would level off before the goal. The calculator says so and shows where it levels off.

Plan by weekly pace and the calculator converts it with the rule's own ratio: 1 lb a week is a 500-calorie daily deficit (3,500 ÷ 7), and 0.5 kg a week is about 550. The 3,500 rule date then matches your pace exactly. The falling-needs date shows what happens if you set your calories once for that pace and keep them there.

The 3,500 calorie rule vs Hall's model of falling energy needs

The 3,500 calorie rule is old. Hall (2008) traces it to a calculation, cited to Wishnofsky (1958), that assumes all the weight lost is fat tissue that is 87 percent fat. That assumption gives 3,500 calories per pound, or 32.2 megajoules per kilogram. Hall found the figure fits people with more than 30 kg of body fat reasonably well and runs too high for leaner people, who lose more lean tissue with less stored energy in it.

The bigger problem is time. Hall and colleagues showed that as you lose weight, the energy your body needs falls with it, because a smaller body costs less to run and to move. Their rule of thumb for an average adult with overweight: every 100 kJ (24 calories) a day of change in intake moves body weight by about 1 kg in the end, with half of that change in about a year and 95 percent in about three years. A fixed diet produces a curve that flattens, not a straight line.

Their worked example is a sedentary 100 kg (220 lb) man who cuts 480 calories a day. The 3,500 rule predicts 22.7 kg (50 lb) lost in the first year and more every year after. Hall's full model levels off near 75 kg, about 25 kg lost, and takes roughly a year to get halfway there.

Here is the same split for a 500-calorie daily deficit held for different lengths of time.

What this page simplifies. The calculator does not run Hall's full model. It keeps two numbers: 3,500 calories per pound, so the first day matches the classic rule, and Hall's 100 kJ per kilogram slope for falling needs. That gives one smooth curve. For Hall's 100 kg man it predicts 13.6 kg lost in the first year, against roughly 12.5 kg (half of 25) from the full model and 22.7 kg from the 3,500 rule, and it levels off after 20.1 kg instead of 25. It reaches half of its final loss in about 7 months where the full model takes about a year, because the full model also tracks how fat and lean tissue are lost and how metabolism adapts. For a forecast fitted to your age, sex, height and activity, use the NIH Body Weight Planner, which runs Hall's full model.

Weight loss by date calculator: pick a date, get the pace

Switch the calculator to Target date and it runs the same math backward. Pick the day you want to reach your goal and it returns the weekly pace that date needs, in pounds or kilograms and as a percent of your body weight, plus the daily deficit under each method.

• Average pace = pounds to lose ÷ weeks until the date.
• 3,500 rule deficit = pounds to lose × 3,500 ÷ days until the date.
• Falling-needs deficit = pounds to lose × 10.84 ÷ (1 − e^{−days ÷ 323}). It is larger, because a fixed intake has to start with a bigger cut to reach the same date as a deficit that never shrinks.

Here is what three dates mean for someone going from 200 to 170 lb (90.7 to 77.1 kg).

The 12-week date needs 2.5 lb a week, or 1.25 percent of body weight. That is faster than the 1 to 2 lb a week the CDC describes and above the 0.5 to 1 percent a week that Helms et al. (2014) recommend for keeping muscle. When a date needs more than that, the calculator flags it and shows the earliest date that fits, which is 15 weeks for this example. Moving the date is the safer change. Helms and colleagues note that slower loss is better for holding on to lean mass, and a deeper cut can push your intake below the floors covered further down.

How accurate is this?

A goal date is a forecast, not a promise. Five things move the real date away from either line, and the research puts a number on each.

The first weeks drop faster: water and glycogen

Your body stores carbohydrate as glycogen with three to four parts water (Kreitzman et al. 1992), and a calorie deficit draws it down early. Hall (2008) notes the effect usually shows up within the first week. In Heymsfield et al. (2012), the weight that 23 dieters in the CALERIE study had lost by week 4 carried only 4,858 calories per kilogram. By week 6 it was about 6,041 and held there, still under the 7,700 that the 3,500 rule assumes. So the scale usually beats both lines at first. Neither line models that, and the early drop is not a pace you can count on.

Why the straight line overshoots

Thomas et al. (2013) pooled seven weight loss experiments where food intake was fully supervised or objectively measured: 103 adults with an average deficit of 1,439 calories a day for 31 to 93 days. They lost 20.1 lb on average. The 3,500 rule predicted 27.6 lb, which is 7.4 lb too much. In the five studies where a validated dynamic model could be run, it predicted 18.4 lb against 17.0 lb lost. The longer the diet, the bigger the 3,500 rule's miss, because its straight line never slows. Thomas and colleagues point to two free web tools that run validated dynamic models instead: the NIH Body Weight Planner and the Pennington Biomedical Research Center's Weight Loss Predictor.

Metabolic adaptation

Energy needs also fall a little more than the lost weight explains. Helms et al. (2014) list this metabolic adaptation at 79 to 504 calories a day in studies of people with overweight. At the far end, 14 contestants from a televised weight loss competition burned 499 calories a day less at rest than their size predicted six years later (Fothergill et al. 2016). The falling-needs estimate leaves adaptation out, so for most people it is still a little optimistic.

Plateaus

Most diet programs run outside a lab reach their lowest weight at 6 to 8 months, then regain. Hall et al. (2011) point out that their model, with perfect adherence, plateaus only after several years, so the usual early plateau more likely reflects intake drifting back up. Polidori et al. (2016) measured how strong that pull is: appetite rose by about 100 calories a day for every kilogram lost, more than three times the drop in energy needs. A plateau around month six is common and does not mean the plan failed.

Body fat and sex

People with more body fat lose a larger share of fat, and each kilogram of it holds more stored energy, so the same deficit moves the scale a little more slowly at first (Hall 2008). In a 13-week study of 75 adults in Kiel, Germany, each kilogram the women lost carried 6,804 calories against 6,119 for the men (Heymsfield et al. 2012). The calculator uses one value for everyone.

Read the two dates as a range. The 3,500 rule date is the earliest you could expect, and only if you keep lowering your intake as you lose. The falling-needs date is closer to what a fixed diet delivers, before adaptation and appetite are counted. Weigh in on the same day each week and compare your trend with the milestone table rather than any single reading.

Worked examples: goal dates for seven plans

Seven plans run through the calculator. The falling-needs column assumes you set your intake once at the start and keep it.

Three patterns stand out. A deficit that is large next to the weight you want to lose stays close to the 3,500 rule: 15 lb at 500 calories a day takes 18.1 weeks instead of 15. A small deficit drifts further: 300 calories a day stretches 25 weeks to 36. And 60 lb at 500 calories a day is never reached on a fixed intake, because energy needs fall by about 650 calories a day over that much weight, more than the whole deficit.

How long will it take to reach my goal weight safely?

For most adults, the answer is months rather than weeks. Two guides set the pace this calculator checks against. The CDC notes that people who lose about 1 to 2 lb a week are more likely to keep the weight off. Helms et al. (2014) recommend 0.5 to 1 percent of body weight a week to hold on to muscle. The calculator flags a pace above the lower of the two: 2 lb a week, or 1 percent of your body weight if that is less. At 150 lb, the limit is 1.5 lb a week.

Pace as a percent matters because the same pound is a bigger share of a smaller body. Two pounds a week is 1 percent of 200 lb and 1.33 percent of 150 lb.

Calories have a floor too. The 2013 AHA/ACC/TOS obesity guideline prescribes 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men in weight loss programs, usually as a deficit of 500 to 750 calories a day. It reserves very-low-calorie diets, under 800 calories a day, for medical settings with supervision. Add your maintenance calories from the TDEE calculator and the result card shows your daily intake. It flags an intake below 1,200, and notes one below 1,500, the starting point for men.

How to keep your goal date on track

Recalculate maintenance as you go. By Hall's slope, every 10 lb you lose lowers your energy needs by about 108 calories a day. Running the TDEE calculator again every 10 to 15 lb keeps your deficit near its starting size, which pulls your real date toward the 3,500 rule line.

Watch the weekly trend. Daily weight moves with water, salt and food in your gut. Compare a weekly average with the milestone table. To see how far you have come as a share of your starting weight, use the weight loss percentage calculator.

Lift while you lose. Hall (2008) notes that resistance exercise and a higher protein intake may change how much of the weight you lose comes from fat rather than lean tissue. If you train at home, our roundup of the best workout apps for weight loss compares programs you can run with dumbbells and bodyweight.

Pick a goal you can hold. If you are unsure what goal makes sense for your height, the ideal weight calculator compares the published formulas side by side.

When to ignore this calculator

Both methods describe healthy adults who lose weight by eating less or moving more. In the cases below, skip the date or ask a clinician first.

• Pregnancy or breastfeeding. Calorie needs rise, and weight loss goals belong with your obstetric care team.
• Eating disorders or recent recovery. Goal dates and calorie targets can work against recovery. Work with a clinician or dietitian who specializes in eating disorders.
• Diabetes or medicines that lower blood sugar. A calorie cut can cause low blood sugar on insulin or some tablets. Ask your care team how to adjust first.
• Weight loss medicines or surgery. GLP-1 medicines and bariatric surgery change appetite and follow their own timelines. Your prescriber or surgical team should set the pace.
• Children and teenagers. The calculator is for adults 18 and over. Growing bodies need a pediatrician's guidance.
• Unplanned weight loss. If you are losing weight without trying, see a doctor rather than a calculator.

Related reading

References

1. Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA. "Quantification of the effect of energy imbalance on bodyweight." Lancet. 2011;378(9793):826-837. doi:10.1016/S0140-6736(11)60812-X, PMC3880593
2. 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." Int J Obes (Lond). 2013;37(12):1611-1613. doi:10.1038/ijo.2013.51, PMC4024447
3. Hall KD. "What is the required energy deficit per unit weight loss?" Int J Obes (Lond). 2008;32(3):573-576. doi:10.1038/sj.ijo.0803720, PMC2376744
4. Wishnofsky M. "Caloric equivalents of gained or lost weight." Am J Clin Nutr. 1958;6(5):542-546. doi:10.1093/ajcn/6.5.542. Cited by Hall (2008) as the origin of the 3,500 calorie rule; the paper has no online abstract, so its derivation is described here as Hall gives it.
5. Heymsfield SB, Thomas D, Martin CK, Redman LM, Strauss B, Bosy-Westphal A, Müller MJ, Shen W, Martin Nguyen A. "Energy content of weight loss: kinetic features during voluntary caloric restriction." Metabolism. 2012;61(7):937-943. doi:10.1016/j.metabol.2011.11.012, PMC3810417
6. Kreitzman SN, Coxon AY, Szaz KF. "Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition." Am J Clin Nutr. 1992;56(1 Suppl):292S-293S. doi:10.1093/ajcn/56.1.292S
7. Polidori D, Sanghvi A, Seeley RJ, Hall KD. "How strongly does appetite counter weight loss? Quantification of the feedback control of human energy intake." Obesity (Silver Spring). 2016;24(11):2289-2295. doi:10.1002/oby.21653, PMC5108589
8. Fothergill E, Guo J, Howard L, Kerns JC, Knuth ND, Brychta R, Chen KY, Skarulis MC, Walter M, Walter PJ, Hall KD. "Persistent metabolic adaptation 6 years after 'The Biggest Loser' competition." Obesity (Silver Spring). 2016;24(8):1612-1619. doi:10.1002/oby.21538, PMC4989512
9. Helms ER, Aragon AA, Fitschen PJ. "Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation." J Int Soc Sports Nutr. 2014;11:20. doi:10.1186/1550-2783-11-20
10. Jensen MD, Ryan DH, Apovian CM, et al. "2013 AHA/ACC/TOS guideline for the management of overweight and obesity in adults." Circulation. 2014;129(25 Suppl 2):S102-S138. doi:10.1161/01.cir.0000437739.71477.ee, PMC5819889
11. Centers for Disease Control and Prevention. "Steps for Losing Weight." cdc.gov
12. National Institute of Diabetes and Digestive and Kidney Diseases. "Body Weight Planner." niddk.nih.gov/bwp

How this calculator differs from typical weight loss date calculators

Most online weight loss date calculators divide the weight you want to lose by a weekly pace, or multiply it by 3,500 calories per pound, and print one date as if your body burned the same energy at 170 lb as at 200 lb. Few say that this rule has been tested against measured weight loss and found to overshoot, and few warn when a target date needs a pace or an intake below what clinical guidelines recommend.

This calculator prints the classic date next to a second date in which your energy needs fall as you lose, using the slope from Hall et al. (2011), and it says where a fixed intake levels off when the goal is out of reach. It works in both directions, from a deficit or pace to a date and from a date to a pace and deficit. It reports pace as a percent of body weight, flags it against the CDC and Helms et al. guidance, checks your intake against the 2013 obesity guideline when you add maintenance calories, and says plainly where it simplifies the research model it is built on. It shows no date until both weights and your plan sit inside realistic adult ranges.