Project your weight loss timeline based on daily calorie intake and activity level
This calculator provides estimates only. Consult your GP or a healthcare professional for personalised advice.
This calorie weight loss calculator projects how long it will take to reach your target weight based on your daily calorie intake and activity level. It uses the Mifflin-St Jeor equation to calculate your Total Daily Energy Expenditure (TDEE) and then estimates your weekly weight loss based on the calorie deficit you create. Weight loss fundamentally comes down to energy balance: consuming fewer calories than your body burns creates a deficit, and your body draws on stored energy (primarily body fat) to make up the difference. One kilogram of body fat contains approximately 7,700 calories, so a daily deficit of 500 kcal results in roughly 0.45 kg (1 lb) of weight loss per week. The NHS recommends a safe and sustainable rate of weight loss of 0.5 to 1 kg per week. More rapid weight loss may lead to muscle loss, nutritional deficiencies, and is generally harder to maintain long-term. The NHS Start4Life and Better Health programmes provide free support for people looking to manage their weight in the UK. This calculator builds on the Mifflin-St Jeor equation, published in 1990, which is considered the most accurate widely available formula for estimating basal metabolic rate (BMR). By multiplying BMR by an activity factor, we get your TDEE, the total number of calories your body needs each day to maintain its current weight. If you need to convert between stones and kilograms, 1 stone equals 6.35 kg. For example, 12 stone is 76.2 kg and 10 stone is 63.5 kg.
To project your weight loss timeline: 1. Enter your age, sex, current weight (in kg), and height (in cm). If you know your weight in stones, multiply by 6.35 to convert to kilograms. For height, 5 foot 5 inches equals approximately 165 cm. 2. Select your activity level. Be honest about your typical weekly activity. Sedentary means a desk job with little exercise; lightly active means 1-3 exercise sessions per week; moderately active means 3-5 sessions; very active means 6-7 sessions; extremely active means a physical job combined with regular training. 3. Enter your planned daily calorie intake. This is the number of calories you plan to consume each day. The NHS recommends a minimum of 1,200 kcal for women and 1,500 kcal for men. 4. Enter your target weight in kilograms. This is the weight you want to reach. 5. Review your results. The calculator shows your TDEE, BMR, daily calorie deficit, estimated weekly loss, and the number of weeks and months to reach your target. If your intake exceeds your TDEE, the calculator will indicate that you will maintain or gain weight at that level. 6. Check for safety warnings. If your planned intake is below the NHS minimum thresholds, a warning will be displayed.
The calculator uses the Mifflin-St Jeor equation for Basal Metabolic Rate: For males: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5 For females: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161 TDEE = BMR x activity multiplier Activity multipliers: Sedentary (little exercise): 1.2 Lightly active (1-3 days/week): 1.375 Moderately active (3-5 days/week): 1.55 Very active (6-7 days/week): 1.725 Extremely active (physical job + training): 1.9 Daily calorie deficit = TDEE - planned daily intake Weekly weight loss (kg) = (daily deficit x 7) / 7,700 Weeks to target = (current weight - target weight) / weekly loss The 7,700 figure represents the approximate number of calories stored in one kilogram of body fat. This is an average; the actual value varies slightly between individuals. The calculation assumes a constant TDEE throughout the weight loss period, though in reality, TDEE decreases as weight drops.
Inputs: Age: 30. Sex: Female. Weight: 80 kg (12 stone 8 lbs). Height: 165 cm. Activity: Lightly active. Intake: 1,500 kcal. Target: 70 kg (11 stone).
Inputs: Age: 25. Sex: Male. Weight: 90 kg (14 stone 2 lbs). Height: 180 cm. Activity: Sedentary. Intake: 2,000 kcal. Target: 80 kg (12 stone 8 lbs).
Inputs: Age: 30. Sex: Female. Weight: 80 kg. Height: 165 cm. Activity: Lightly active. Intake: 2,500 kcal. Target: 70 kg.
The Mifflin-St Jeor equation is considered the most accurate BMR formula for the general population, though individual variation exists. Factors such as body composition (muscle-to-fat ratio), genetics, hormonal status, and medications can all influence actual metabolic rate. As you lose weight, your BMR and TDEE decrease because a lighter body requires less energy to maintain. This means the rate of weight loss will gradually slow over time, even at the same calorie intake. Many people experience a "plateau" effect for this reason. Re-calculating your TDEE every few weeks or after losing 5 kg can help keep your plan on track. The NHS recommends combining dietary changes with regular physical activity for sustainable weight loss. Even modest increases in activity, such as a daily 30-minute walk, can increase TDEE by 100-200 kcal per day. The NHS Better Health website offers free tools and 12-week plans to support weight management. Very low calorie diets (VLCDs) of fewer than 800 kcal per day should only be followed under medical supervision. The NHS advises against prolonged use of VLCDs without a GP or dietitian guiding the process, as they carry risks including nutritional deficiency, muscle loss, and gallstones. For conversions: 1 stone = 6.35 kg = 14 lbs. Common UK weight benchmarks: 10 stone = 63.5 kg, 12 stone = 76.2 kg, 14 stone = 88.9 kg, 16 stone = 101.6 kg.