Weight loss calculator – your goal date
This weight loss calculator shows how long you need to reach your goal weight at a fixed calorie deficit, and which date that gives. It accounts for falling energy needs: as you get lighter you burn less and the deficit shrinks.
Source: Mifflin-St Jeor, Mifflin MD, St Jeor ST et al. (1990): A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 51(2):241–247. Updated: .
How it is calculated
How the weight loss calculator works
Body weight changes when energy intake differs from energy use. The calculator first works out your daily energy needs (basal metabolic rate by Mifflin-St Jeor × activity factor PAL). Your intake then sits below that by the deficit you choose. On paper you lose deficit ÷ 7,700 kg per day – the rule of thumb of about 7,700 kcal per kilogram (3,500 kcal per pound). After that it recalculates day by day: at a lower weight your basal rate falls, the deficit gets smaller and loss slows down.
Example: woman, 35, 170 cm (5 ft 7 in), 80 kg (176 lb), goal 70 kg (154 lb), PAL 1.53, deficit 500 kcal. Starting needs 2,336 kcal, intake 1,836 kcal. The simple sum gives 10 kg × 7,700 ÷ 500 = 154 days. With falling energy needs it is about 184 days – a little over six months.
How to use the calculator
- Enter your body data, goal weight and activity level.
- Choose the daily calorie deficit: 250, 500 or 750 kcal.
- Read the date, duration, daily intake and the progress in four-week steps.
When no timeline is shown
- Intake below 1,200 kcal or below your basal rate: not advisable without medical supervision. Choose a smaller deficit.
- Underweight goal: with a goal BMI below 18.5 (WHO) there is no plan.
- Plateau: at the chosen deficit your weight settles between start and goal on paper; only a larger deficit or a higher goal helps.
Limits of the calculation
The 7,700 kcal rule is a simplification. Research shows that the energy gap per kilogram lost shrinks over time and that fat and muscle differ (Hall 2008, Lancet 2011). The date is therefore a guide, not a promise. Pregnant or breastfeeding women, teenagers and people with medical conditions need individual advice.
Related: your daily needs are in the TDEE calculator, a comfortable weight range in the ideal weight calculator, and the BMI calculator classifies your result.
Frequently asked questions
How long does it take to lose 10 kg (22 lb)?
At a 500 kcal daily deficit expect about 5 to 6 months (184 days for the example). At 250 kcal it is around 15 months, at 750 kcal a little over 3.5 months – as long as intake does not drop below 1,200 kcal.
How do I calculate my calorie deficit?
Your calorie deficit is your daily energy needs minus what you eat. The calculator works out your needs from age, sex, height, weight and activity, subtracts the deficit you choose (250, 500 or 750 kcal) and shows the daily intake that goes with it: 2,336 − 500 = 1,836 kcal in the example.
How big a calorie deficit makes sense?
A moderate deficit of 250 to 500 kcal a day is usually sustainable. Larger deficits quickly push intake under 1,200 kcal, where the calculator shows no plan.
Why does weight loss slow down over time?
A lighter body uses less energy. At the same intake the deficit shrinks and weekly loss gets smaller. The calculator takes this into account.
Does this work with exercise?
Yes, if you pick the activity factor that matches your week: training raises your energy use and with it the intake you can have at the same deficit.
How accurate is the date?
It is an estimate. Fluctuations from water, salt and digestion easily reach one to two kilograms. Check your trend over several weeks.
Sources and legal basis
- Mifflin-St Jeor: Mifflin MD, St Jeor ST et al. (1990): A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 51(2):241–247
- FAO/WHO/UNU 2004: FAO/WHO/UNU (2004): Human energy requirements – Report of a Joint Expert Consultation, Chapter 5, Tables 5.1 and 5.3 (PAL)
- Hall KD (2008): What is the required energy deficit per unit weight loss? Int J Obes 32:573–576 (limits of the 7,700 kcal rule of thumb)
- Hall KD et al. (2011): Quantification of the effect of energy imbalance on bodyweight. Lancet 378:826–837 (dynamisches Modell)
- WHO TRS 894: WHO Technical Report Series 894 – Obesity: preventing and managing the global epidemic (2000), Table 2.1 (Untergewicht BMI < 18,5)
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