How Many Kilos Can You Lose in a Month? Working Back from 1 kg of Body Fat = 7,200 kcal

Think of 1 kg of body fat as about 7,200 kcal

Fat holds about 9 kcal of energy per gram, but body fat also contains water and other things, so losing 1 kg of body fat is said to take about 7,200 kcal. With this figure, a diet plan can be set up with the following formula.

Your daily calorie intake target is "daily calorie burn − daily deficit". Daily calorie burn is basal metabolic rate × physical activity level. How to work it out is explained in basal metabolic rate formulas and daily calorie burn.

How many months to lose 5 kg? Comparing periods

Here's a comparison for a 30-year-old woman, 160 cm tall and 60 kg, with a "moderate" activity level (basal metabolic rate 1,253 kcal, daily calorie burn 2,193 kcal), aiming for 55 kg. A month is counted as 30 days.

A plan to lose 5 kg in 1 month puts daily intake at 993 kcal, below the basal metabolic rate (1,253 kcal). Eating below your basal metabolic rate for long means losing muscle as well as fat, which lowers your metabolism and makes rebound weight gain more likely. Over 3 months it's 400 kcal a day, which works out to roughly one bowl of rice (about 230 kcal for 150 g) plus one small snack.

For a 40-year-old man, 170 cm and 75 kg (daily calorie burn 2,763 kcal), aiming for 65 kg, it's 800 kcal a day over 3 months (4.4% of body weight per month, "fast") or 400 kcal a day over 6 months (2.2%, "standard"). The more you want to lose, the longer the period you need.

Judge a reasonable pace as "% of body weight per month"

Even the same 2 kg a month puts a different load on the body for someone weighing 50 kg and someone weighing 90 kg. So it's clearest to think of pace as "what percentage of current body weight to lose per month", and the BMI & Healthy Weight Calculator shows it in four levels.

Losing more than 5% of your body weight in a month puts a heavy load on the body and tends to lead to muscle loss and rebound. The Japan Society for the Study of Obesity's guidelines also set a weight-loss goal of at least 3% of current body weight over 3 to 6 months. Rather than losing a lot quickly, keeping to a "standard" pace or slower gets you there sooner in the end.

How many minutes of exercise?

Calories burned by exercise can be calculated using METs, a measure of exercise intensity. Subtracting the 1 MET you'd burn even at rest gives "(METs − 1) × body weight (kg) × hours × 1.05" as the extra calories burned by exercise.

The table shows values per hour. If a 60 kg person wants to lose 5 kg in 3 months (400 kcal a day) through exercise alone, that's about 152 minutes of walking or about 63 minutes of jogging every day. Burning a lot of calories through exercise alone is hard, so a realistic approach is to combine them, such as 200 kcal from food and 200 kcal from exercise (about 76 minutes of walking).

Why weight doesn't come off as calculated

• In the first 1–2 weeks you lose water, so weight may drop faster than calculated. It's natural for the loss to slow down after that.
• As you lose weight, your basal metabolic rate and calorie burn fall too. Even eating the same amount, the daily gap shrinks as weight loss progresses.
• Cutting food too sharply puts the body into energy-saving mode, making a plateau, where weight loss seems to stop, more likely.
• Body weight fluctuates by 1–2 kg a day with water, bowel movements and salty meals. Rather than reacting to each day's number, look at the weekly average.

The calculation is for getting a sense of whether a pace will get you there; actual weight doesn't fall in a straight line. Compare against your actual weight every 2–4 weeks, and if progress differs greatly from the plan, revise the period or calorie intake.

Work back from a target weight and period

1. 1

   Enter height, weight and age

   Enter your height and weight in the BMI & Healthy Weight Calculator and open the "Target weight & diet" tab. Sex, age and activity level are used to calculate calorie burn.

2. 2

   Enter your target weight and period

   Enter your target weight, and enter the period in days, weeks or months. You can also choose from suggestion buttons such as "Standard weight", "−3 kg" or "−5% of body weight".

3. 3

   Check your calorie intake and pace

   You'll see your daily calorie intake target, daily deficit, change per month and pace. You can also check a table comparing 1, 2, 3, 4, 6 and 12 months, and the time needed if you burn the deficit through exercise alone.

A warning appears for plans where calorie intake falls below your basal metabolic rate or where the target weight would be underweight (BMI below 18.5). For choosing a target weight, see standard weight and "beauty weight" by height.

FAQ

How many kcal a day do I need to cut to lose 1 kg in a month?

1 kg of body fat is about 7,200 kcal, so 7,200 ÷ 30 days = about 240 kcal a day. It can come from eating less or exercising more. For 2 kg in a month it's 480 kcal a day, and for 3 kg it's 720 kcal a day.

How many kcal a day should I eat to lose 5 kg in 3 months?

Cut 5 kg × 7,200 kcal ÷ 90 days = 400 kcal a day. For a 30-year-old woman, 160 cm and 60 kg, with a "moderate" activity level, subtracting 400 kcal from a daily calorie burn of about 2,193 kcal gives a target intake of about 1,793 kcal.

How many kilos a month can I lose without overdoing it?

A guideline is about 2–3.5% of body weight per month: about 1.2–2.1 kg at 60 kg and about 1.5–2.6 kg at 75 kg. Losing more than 5% of body weight in a month tends to lead to muscle loss and rebound, so it's best to extend the period.

How do I calculate calories burned by walking?

(METs − 1) × body weight (kg) × hours × 1.05 gives the extra calories burned by exercise. Walking at a normal pace is 3.5 METs, so a 60 kg person walking for 1 hour burns (3.5 − 1) × 60 × 1 × 1.05 = about 158 kcal.