Calorie Calculator to Gain Weight

Gaining weight comes down to eating a little more than your body burns, every day, for weeks. The calculator works that out in three steps. First it estimates your basal metabolic rate (BMR) with the Mifflin-St Jeor equation: 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 for men or minus 161 for women. Then it multiplies BMR by an activity factor to get your maintenance calories, the intake that keeps your weight steady. Finally it adds a surplus on top and splits the total into protein, fat and carbohydrates.

How Big a Surplus to Use

Bigger is not better. A 2019 review of off-season bodybuilding nutrition by Iraki and colleagues recommends a surplus of about 10-20% above maintenance, aiming to gain 0.25-0.5% of body weight per week, with advanced lifters at the lower end (5-10% and about 0.25% a week). The calculator's three options sit on that range: Lean +10%, Standard +15% and Faster +20%. For the estimated weekly gain, it pairs the ends of the two ranges (+10% with 0.25% a week, +20% with 0.5%) and takes the midpoint, 0.375%, for Standard. The NHS advice for underweight adults lands in the same place, suggesting around 300 to 500 extra calories a day.

Nobody knows the exact surplus that maximises muscle growth. A 2019 review in Frontiers in Nutrition calls it unknown and suggests starting conservatively at about 1,500-2,000 kJ a day (roughly 360-480 calories). It also cites a 100-day overfeeding study in young lean men in which about 2 kg of fat was gained for each 1 kg of lean mass. That is why the weekly gain here is an estimate drawn from the target rates above rather than a fixed calories-per-kilogram rule: how much of the surplus becomes muscle, fat or extra movement differs from person to person.

Protein and Resistance Training

A surplus supplies the energy; resistance training is what directs it toward muscle. On protein, a 2018 meta-analysis in the British Journal of Sports Medicine found that gains in lean mass from resistance training levelled off at about 1.62 g per kg of body weight per day, with the upper confidence limit at 2.2 g/kg. Iraki and colleagues recommend 1.6-2.2 g/kg spread over meals of 0.40-0.55 g/kg each, and the International Society of Sports Nutrition gives 1.4-2.0 g/kg for most exercising people. The calculator starts at 1.6 g/kg; pick a higher setting if you find protein easy to eat. For a closer look, see the protein calculator for muscle gain and our guide to daily protein requirements.

Fat is set as a share of calories within the adult range of 20-35% from the National Academies, which also puts carbohydrates at 45-65%. Carbs take whatever is left, which keeps plenty of fuel for training.

Calorie-Dense Food Ideas

If a bigger appetite is the hard part, make each bite count. The NHS suggests:

• Smaller meals more often, with snacks such as yogurt or rice pudding in between.
• Add-ons that pack energy: cheese, nuts and seeds on top of meals you already eat.
• Protein with every meal: beans, pulses, fish, eggs or lean meat.
• Drinks between meals, not before them: milkshakes add calories, but drinking just before eating can fill you up.

The same advice warns against leaning on chocolate, cakes and sugary drinks. For full days of food built around a surplus, see our bulking meal plan and how many calories you need to gain muscle.

Tracking Progress

Weigh yourself at the same time of day a few times a week and compare weekly averages rather than single days, since water and food in the gut move the scale from day to day. After a few weeks, compare your average rate with the estimate. If you are gaining faster than about 0.5% of body weight a week, step down a tier; if the scale has not moved, step up one. Recalculate as your weight rises, because maintenance calories rise with it.

When to Talk to a Doctor

If you have lost weight without changing how you eat or move, or if food has become a way of coping with feelings, the NHS recommends speaking to a GP: unexplained weight loss can be a sign of an underlying condition. It is also worth a check-up before you start if your BMI is under 18.5, which the CDC classes as underweight for adults 20 and older. A doctor or dietitian can help you gain at a pace that suits you. This calculator is for healthy adults and is not a substitute for that advice.