To gain weight, you need to eat more calories than your body burns each day. For most people, adding 300 to 500 calories above their maintenance level produces steady, healthy weight gain of about 1 to 2 pounds per week. The tricky part is figuring out your personal maintenance number, because it varies significantly based on your size, age, sex, and how active you are.
How to Estimate Your Maintenance Calories
Your maintenance calories, sometimes called your total daily energy expenditure, represent the amount of energy your body uses in a full day. This includes everything from keeping your organs running to walking around and exercising. The most widely used method to estimate this number starts with a formula called the Mifflin-St Jeor equation, which calculates your basal metabolic rate (the calories your body burns at complete rest) and then adjusts for activity.
The formula works like this:
- Males: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
- Females: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Once you have that number, multiply it by an activity factor:
- Sedentary (desk job, little exercise): × 1.2
- Lightly active (light exercise 1–3 days/week): × 1.375
- Moderately active (moderate exercise 3–5 days/week): × 1.55
- Active (hard exercise 6–7 days/week): × 1.725
- Very active (intense daily training or physical job): × 1.9
For example, a 25-year-old male who weighs 150 pounds (68 kg), stands 5’10” (178 cm), and exercises moderately would calculate: (10 × 68) + (6.25 × 178) – (5 × 25) + 5 = 1,672 calories at rest. Multiplied by 1.55, his estimated maintenance is about 2,592 calories per day. To gain weight, he’d aim for roughly 2,900 to 3,100 calories daily.
How Big Your Surplus Should Be
A surplus of 300 to 500 calories per day is a solid starting point for most people. This range typically produces 1 to 2 pounds of weight gain per week, which is considered a healthy pace. Going much higher than that doesn’t necessarily mean faster muscle growth. It often just means more fat storage, especially if you’re not training hard.
If you’re someone who has always struggled to gain weight, you may need to push closer to 500 or even 700 extra calories. That’s because your body has a built-in resistance mechanism. When you overeat, your body ramps up something called non-exercise activity thermogenesis: the calories you burn through fidgeting, maintaining posture, and moving around during everyday life. In one study where participants overate by 1,000 calories per day for eight weeks, the increase in this unconscious movement varied wildly between people, ranging from burning nearly 100 fewer calories to burning 692 extra calories per day. Some people’s bodies effectively burned off 69% of the surplus through this mechanism alone, while others stored most of it. This is a big reason why some people feel like they “can’t gain weight no matter what.” Your target surplus might need to be larger than someone else’s to produce the same result.
Why the Scale Might Not Move Right Away
Give any new calorie target at least two to three weeks before adjusting. Weight fluctuates daily due to water retention, digestion, and hydration levels. Weigh yourself at the same time each day (ideally in the morning, before eating) and track the weekly average. If your average weight hasn’t budged after two full weeks, add another 200 to 300 calories per day and reassess. This iterative approach is more reliable than trying to nail the perfect number on day one.
What to Eat to Hit Your Target
Eating enough calories to gain weight is harder than it sounds, especially if you don’t have a big appetite. The key is choosing foods that pack a lot of energy into small volumes. Two tablespoons of peanut or almond butter deliver about 190 calories. An ounce of nuts or seeds provides 160 to 200 calories. Half an avocado adds 100 to 150 calories. A tablespoon of olive oil or butter is 100 calories and can be stirred into almost anything. These additions don’t require you to eat dramatically more food. They just make the food you’re already eating more calorie-dense.
Some practical swaps: use whole milk (150 calories per cup) instead of skim. Choose full-fat Greek yogurt (120 to 160 calories per 6 ounces). Add cheese to meals (115 calories per ounce). Snack on dried fruit like raisins, apricots, or figs, which pack 160 to 185 calories into just 2 ounces. Protein-fortified milk, at 211 calories per cup, is one of the easiest ways to add both calories and protein without extra chewing.
Liquid Calories Can Help
If you struggle to eat enough solid food, liquid calories are a powerful tool. Your body registers liquids very differently than solids. Research shows that when people consume the same number of calories as a liquid versus a solid, they don’t compensate by eating less later in the day. In one four-week crossover study, participants gained weight when extra carbohydrate calories came from beverages but not when the same calories came from solid food. This happens partly because liquids move through your stomach faster and trigger weaker fullness signals.
Smoothies are ideal because you can load them with calorie-dense ingredients: whole milk, nut butter, banana, oats, protein powder, and a drizzle of honey can easily reach 600 to 800 calories in a single glass. Soups are an interesting exception among liquids. Because you eat soup slowly (under 100 grams per minute, similar to solid food), it’s more filling than a drink you can gulp down. For pure calorie-adding purposes, drinkable shakes and smoothies work better than soup.
How Much Protein You Need
Protein matters more during a calorie surplus than at any other time, because it determines how much of your weight gain is muscle versus fat. If you’re resistance training, aim for 1.2 to 1.7 grams of protein per kilogram of body weight per day. For a 150-pound (68 kg) person, that’s roughly 82 to 116 grams daily. A general macro breakdown that supports muscle gain is about 30 to 35% of your calories from protein, 40 to 50% from carbohydrates, and 20 to 30% from fats.
You don’t need to track every gram obsessively. A simpler approach: include a protein source at every meal (eggs, meat, fish, beans, tofu, dairy) and fill the rest of your plate with starchy carbs and healthy fats. If you’re consistently hitting your calorie target and training with weights, the protein usually takes care of itself as long as you’re not filling up on empty-calorie junk food.
Strength Training Changes the Equation
Eating in a surplus without resistance training will still make you gain weight, but most of that gain will be fat. Strength training sends the signal your body needs to direct extra calories toward building muscle tissue. You don’t need to live in the gym. Two to four sessions per week focusing on compound movements (squats, deadlifts, presses, rows) is enough for most people to shift the ratio of their weight gain toward lean mass. The combination of a moderate calorie surplus, adequate protein, and progressive resistance training is the most reliable formula for gaining weight you’ll actually want to keep.