Weight Loss Calculator
See the date you could reach your goal weight. This calculator slows down as you get lighter, the way real bodies do, and never plans below a safe floor.
- Free, no signup
- Updated 12 October 2026
- Stays in your browser
Fill in your details and your answer appears here as you type.
Why one calorie number is not enough
Most calculators give you one daily calorie number and a straight line to your goal (about 7,700 calories per kg, or 3,500 per lb). Real bodies do not work that way. As you get lighter you burn less, so the same food makes a smaller and smaller deficit, and the loss slows to a stop above your goal.
The fix is simple: check in every 4 weeks and lower your calories a little. Here is the difference for three example people on the steady pace, from the same model this calculator uses.
| Example | Steady plan with check-ins | Same calories, never adjusted | Straight-line rule says |
|---|---|---|---|
| Man, 35, 180 cm, 90 to 80 kg, moderately active | 23 weeks (2,500 calories, stepping down to 2,270) | 46 weeks, then it stalls near 78.5 kg | 29 weeks |
| Woman, 40, 165 cm, 85 to 72 kg, lightly active | 33 weeks (1,690 calories, stepping down to 1,440) | 59 weeks, then it stalls near 69 kg | 36 weeks |
| Woman, 30, 168 cm, 70 to 63 kg, mostly sitting | 23 weeks (1,450 calories, stepping down to 1,380) | 29 weeks, then it stalls near 58.6 kg | 28 weeks |
Your date is a window, not a promise. Water, salt and hormones move the scale by a kilo or two from day to day, so compare weekly averages with the check-in weights.
Pick a pace you can keep
- Gentle (0.25% of your weight a week): small changes you barely notice, below the range guidelines give, and the most food each day.
- Steady (0.5% a week): inside the 0.5 to 1 kg (1 to 2 lb) a week that the CDC and the 2013 AHA/ACC/TOS guideline advise for most people.
- Fastest safe (1% a week, at most 1 kg): the top of that range, for a set date. Keep protein high and lift weights: a review of the research found both help keep muscle while losing weight (Cava and others, 2017).
Losing 5% of your starting weight is where guidelines report health benefits such as better blood pressure and blood sugar, and 10% brings more. The calculator marks both dates.
What to eat once you get there
Your maintenance calories after a loss are lower than they were before you started: a smaller body burns less. The calculator shows that number, so the end of the diet is a small step up rather than a jump back to old habits. People who keep weight off tend to keep weighing themselves regularly and stay active (National Weight Control Registry, Wing and Phelan, 2005).
How we got it
We run a day-by-day energy balance model based on the published NIH body weight equations (Hall and others, 2011). As you lose weight you burn a little less, and the loss splits between fat and lean mass by your body fat (Forbes). Each pace is re-planned every 4 weeks, like a check-in: gentle loses 0.25% of your weight a week, steady 0.5% and the fastest safe pace 1% (at most 1 kg). Calories never go below your resting energy or 1,200 (women) / 1,500 (men), plus 400 while breastfeeding. The date is a window of about one week either side per month ahead, because real bodies vary.
Updated . Sources: Hall and others, 2011, The Lancet, quantification of the effect of energy imbalance on bodyweight; Hall and Chow, 2013, International Journal of Obesity, why is the 3500 kcal per pound weight loss rule wrong?; Forbes, 2000, Annals of the New York Academy of Sciences, body fat content and the body composition response; Mifflin, St Jeor and others, 1990, American Journal of Clinical Nutrition.
The evidence
Every recommendation on this page links here. The badge shows what kind of source it is, so you can judge how strong it is.
- Model
A model of body weight checked against controlled feeding studies: as you lose weight you burn less, so the same diet loses less each month.
Hall et al., 2011, The Lancet: Quantification of the effect of energy imbalance on bodyweight
- Model
The 3,500 calories per pound rule overestimates long-term loss on a fixed diet, because the body uses less energy as weight falls.
Hall and Chow, 2013, International Journal of Obesity: Why is the 3500 kcal per pound weight loss rule wrong?
- Guideline
Advises losing about 1 to 2 pounds (0.5 to 0.9 kg) a week, and says people who lose at a gradual, steady pace are more likely to keep it off.
US Centers for Disease Control and Prevention, Losing Weight, reviewed 2025: Losing Weight
- Guideline
Advises a deficit of 500 to 750 calories a day, or about 1,200 to 1,500 calories a day for women and 1,500 to 1,800 for men.
Jensen et al., 2013 AHA/ACC/TOS guideline, Circulation: 2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity in Adults
- Trial
In 200 adults with obesity, losing weight over 12 weeks or over 36 weeks made no difference to regain: about three quarters of the loss came back within 3 years in both groups.
Purcell et al., 2014, The Lancet Diabetes & Endocrinology: The effect of rate of weight loss on long-term weight management: a randomised controlled trial
- Trial
In 57 adults, a fast diet (500 calories a day for 5 weeks) and a slower one (1,250 a day for 12 weeks) led to the same regain, but the fast diet lost more lean mass.
Vink et al., 2016, Obesity: The effect of rate of weight loss on long-term weight regain in adults with overweight and obesity
- Trial
In over 5,000 adults with type 2 diabetes, losing 5 to 10% of body weight improved blood pressure, blood sugar and blood fats; losing more than 10% helped more.
Wing et al., 2011, Diabetes Care (Look AHEAD): Benefits of modest weight loss in improving cardiovascular risk factors in overweight and obese individuals with type 2 diabetes
- Observational study
People who kept off 30 lb (13.6 kg) or more for at least a year mostly weigh themselves regularly, stay physically active and eat in a consistent way.
Wing and Phelan, 2005, American Journal of Clinical Nutrition: Long-term weight loss maintenance (National Weight Control Registry)
- Review
After weight loss the body burns less than its new size alone would predict, one reason weight comes back easily.
Rosenbaum and Leibel, 2010, International Journal of Obesity: Adaptive thermogenesis in humans
- Review
Eating enough protein and doing resistance training while losing weight help keep muscle.
Cava et al., 2017, Advances in Nutrition: Preserving healthy muscle during weight loss
- Review
How much of a weight change is fat and how much is lean depends on body fat: leaner people lose a larger share as lean mass.
Forbes, 2000, Annals of the New York Academy of Sciences: Body fat content influences the body composition response to nutrition and exercise
- Observational study
The resting energy equation used here, built from measurements in 498 adults.
Mifflin et al., 1990, American Journal of Clinical Nutrition: A new predictive equation for resting energy expenditure in healthy individuals
- Guideline
WHO classes a body mass index under 18.5 as underweight.
World Health Organization, Global Health Observatory: Body mass index
- Guideline
Sets energy needs in pregnancy (none extra in the first trimester, then more each week) and breastfeeding (about 400 extra a day for the first 6 months: 540 for milk minus 140 from body stores, then 380).
National Academies (NASEM), 2023, Dietary Reference Intakes for Energy: Dietary Reference Intakes for Energy
Our own rules of thumb
These are our choices, not findings from a study. We list them so you know which parts are judgement calls.
- Each pace is re-planned every 4 weeks.
- The date window of about one week either side per month ahead.
- Raising calories by 100 to 150 a week after reaching the goal.
Questions
How long will it take to reach my goal weight?
At a steady pace of about 0.5% of your body weight a week, 10 kg (22 lb) takes most people 5 to 8 months. The calculator gives your own date from your size, activity and goal.
Why does weight loss slow down over time?
A smaller body burns fewer calories, so the same food makes a smaller deficit. That is why the plan lowers your calories a little at each 4-week check-in instead of keeping one number for good.
What is a safe rate of weight loss?
Guidelines advise about 0.5 to 1 kg (1 to 2 lb) a week. In two trials, losing faster did not make more weight come back, but a very low calorie diet lost more muscle. This calculator never plans more than 1% of your weight, or 1 kg, a week.
Can I reach my goal weight before a wedding or holiday?
Add the date and the calculator finds the gentlest pace that gets you there. If even the fastest safe pace is too slow, it tells you what you can safely reach by then and when you will get to the rest.
Why is the 3,500 calorie rule wrong?
It assumes every 3,500 calories you cut is a pound of fat for good. In reality your burn falls as you lose weight, and early losses include water and glycogen. NIH researchers found the rule overestimates long-term loss on a fixed diet (Hall and Chow, 2013).
How many calories should I eat after reaching my goal weight?
Fewer than before you started, because a lighter body burns less (Rosenbaum and Leibel, 2010). Raise your calories in small steps of 100 to 150 a week until your weight holds steady, and keep weighing weekly. The step size is our rule of thumb, not from a study.
Is this calculator accurate?
It uses the same kind of model as the NIH Body Weight Planner research, simplified, and shows a date window rather than one exact day. Your own weekly weigh-ins are the best check: if you are ahead or behind after 4 weeks, adjust at the check-in.
Turn this number into a plan
The free bodymaths app keeps your numbers, plans your training and meals around them, and adjusts as you log.
- A dated forecast that updates as you log
- Workouts and meals built around your numbers
- Private: your data stays on your device
Free, no card.