Weight Loss Calculator

How the weight loss calculator works

The calculator builds your daily target in three steps. First it estimates your basal metabolic rate (BMR) — the energy your body uses at complete rest — with the Mifflin–St Jeor equation, which studies have found to be among the more reliable formulas for adults:

• Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161
• Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5

Next, BMR is multiplied by an activity factor (1.2 for a desk job, 1.375 for light activity, 1.55 for moderate and 1.725 for very active) to give your maintenance calories. Finally a daily deficit that matches your weekly goal is taken away, using the common rule of thumb that about 7,700 kcal equals 1 kg of body fat.

Example: a 35-year-old woman, 160 cm and 70 kg, with a light activity level has a BMR of about 1,365 kcal and maintenance of about 1,875 kcal. To lose 0.5 kg a week she would aim for roughly 1,325 kcal a day.

Reading your result

If a goal would push intake below 1,200 kcal a day for women or 1,500 kcal for men, the calculator shows that floor instead. Very low intakes make it hard to get enough protein, iron, calcium and fibre, and are best done only under medical supervision.

A note for Indian and South Asian readers

Because health risk rises at a lower BMI in South Asians, even a modest loss is worthwhile. Losing 5–7% of body weight, together with about 150 minutes of activity a week, lowered the chance of type 2 diabetes in large prevention trials, including one in India. Traditional plates can be heavy on refined rice, rotis and fried snacks; keeping dal, vegetables and curd generous while trimming portions of grains and oil is often an easier change than a strict diet. Our weight loss diet plan builds Indian or global menus at your calorie target.

Women, men, older adults, athletes and pregnancy

• Women may see the scale move up by a kilo or two before a period because of water retention; compare the same point in each cycle. With PCOS, a 5% loss can make periods more regular — see the PCOS diet plan.
• Men usually have a higher BMR at the same weight, so their targets are higher. A waist over 90 cm is a useful early warning even when weight looks normal.
• Older adults lose muscle more easily while dieting. Choose the slowest pace, keep protein up and add strength exercise twice a week.
• Athletes need fuel for training; cutting too hard harms performance, recovery and, in women, menstrual health. Aim for small deficits away from competition.
• Pregnancy is not a time to diet. When breastfeeding, the body needs extra energy, so any loss should be slow and agreed with your doctor.

Why real results differ from the estimate

Formulas can be off by 10% or more for an individual. Early losses are partly water, and as you get lighter your maintenance needs fall, so progress naturally slows; the 7,700 kcal rule also overstates long-term loss. Treat the number as a starting point, track your weight weekly for a month and adjust by 100–200 kcal if nothing changes. Sleep, stress, medicines and medical conditions such as an underactive thyroid also play a part.

When to talk to a doctor first

• you take medicine for diabetes or blood pressure, as doses may need to change as you lose weight
• you have kidney, heart or liver disease, or your BMI is 35 or above
• you are under 18, pregnant or breastfeeding
• you have had an eating disorder, or dieting makes you anxious around food
• you are losing weight without trying

Common questions

Sources: Mifflin MD et al. A new predictive equation for resting energy expenditure (1990) · Hall KD et al. Quantification of the effect of energy imbalance on bodyweight (Lancet 2011) · NIH NIDDK: Body Weight Planner · Ramachandran A et al. Indian Diabetes Prevention Programme (2006) · WHO: Obesity and overweight fact sheet

Checked against the sources listed. This is general health information, not a diagnosis or personal medical advice — please speak to your doctor about your own situation.