To gain weight at a healthy rate, you need to eat roughly 300 to 500 calories more per day than your body burns. That surplus adds up to about 2,000 to 3,500 extra calories per week, which supports a gain of one to two pounds. The exact number depends on your size, activity level, and whether you’re aiming to build muscle or simply add body weight.
Finding Your Starting Number
Before you can figure out how much extra to eat, you need to know how many calories your body uses in a normal day. This is called your total daily energy expenditure, or TDEE. It combines the energy your body burns at rest (breathing, digesting, keeping your heart beating) with the energy you burn through movement and exercise.
The most reliable way to estimate your resting calorie burn is the Mifflin-St Jeor equation, which a systematic review in the Journal of the American Dietetic Association found predicted resting metabolism within 10% of the actual measured value more often than any competing formula. You can find free online calculators that use this equation. You’ll enter your age, sex, height, and weight, and get a baseline number.
From there, you multiply by an activity factor:
- Sedentary (desk job, no exercise): multiply by 1.2
- Lightly active (light exercise 1 to 3 days per week): multiply by 1.375
- Moderately active (exercise 3 to 5 days per week): multiply by 1.55
- Very active (hard exercise 6 to 7 days per week): multiply by 1.725
The result is your maintenance calories, the amount that keeps your weight stable. A moderately active man who calculates a resting burn of 1,700 calories, for example, would multiply by 1.55 to get roughly 2,635 maintenance calories. To gain weight, he’d aim for about 2,935 to 3,135 calories per day.
How Big Your Surplus Should Be
A surplus of 300 to 500 calories per day is the sweet spot for most people. It takes roughly 2,000 to 2,500 extra calories per week to gain a pound of muscle (when paired with resistance training) and about 3,500 extra calories per week to gain a pound of fat. A moderate surplus tilts the ratio toward muscle rather than fat, especially if you’re lifting weights consistently.
A good target is gaining 0.25% to 0.5% of your body weight per week. For a 175-pound man, that’s about 0.4 to 0.8 pounds per week. For a 135-pound woman, it’s closer to 0.3 to 0.6 pounds per week. Gaining faster than this doesn’t build more muscle. It just stores more fat.
Weigh yourself once a week, at the same time of day, and track the trend over three to four weeks before adjusting. If the scale isn’t moving, add another 200 to 300 calories. If you’re gaining more than a pound per week and you’re not a complete beginner to lifting, scale back slightly.
What to Eat: Protein, Carbs, and Fat
Calories matter most for weight gain, but where those calories come from determines whether you’re building muscle or just adding body fat.
Protein is the priority. If you’re doing any kind of resistance training, aim for 1.2 to 1.7 grams of protein per kilogram of body weight each day. For a 175-pound (80 kg) person, that works out to about 96 to 136 grams of protein daily. Spread it across three to four meals so your body can actually use it for muscle repair.
Fat should make up about 30% or less of your total calories. Within that, keep saturated fat (the kind in butter, fatty meat, and full-fat dairy) under 10% of your daily intake. Fat is calorie-dense at 9 calories per gram, which makes it useful for reaching a surplus without feeling overly stuffed, but the type of fat matters. Prioritize sources like olive oil, nuts, avocados, and fatty fish.
Carbohydrates fill in the rest. They’re your body’s preferred fuel source during exercise, so eating enough of them supports better workouts, which in turn supports better muscle growth. Whole grains, potatoes, rice, oats, fruits, and legumes are all solid choices.
Calorie-Dense Foods That Make It Easier
One of the biggest practical challenges of gaining weight is that eating 500 extra calories per day can feel like a lot of food. Calorie-dense foods help you hit your target without forcing down massive volumes.
- Nuts and nut butters: A quarter cup of roasted nuts packs 160 to 200 calories. Two tablespoons of peanut butter on toast is an easy 200-calorie addition to any meal.
- Avocado: One-third of an avocado has about 80 calories, mostly from heart-healthy fats. Add half an avocado to a sandwich or scramble and you’re up 120 calories without much extra bulk.
- Cheese: A 1.5-ounce serving of cheddar has about 173 calories and 10 grams of protein. Swiss comes in at 167 calories with 11 grams of protein. Grating cheese over meals is one of the easiest ways to add calories.
- Whole milk and yogurt: Switching from skim to whole milk adds about 60 calories per cup. Greek yogurt with granola and honey makes a calorie-dense snack.
- Olive oil and cooking fats: A single tablespoon of olive oil adds roughly 120 calories. Drizzling it over vegetables or using it liberally when cooking quietly increases your intake.
Smoothies are particularly useful if you struggle with appetite. Blending milk, protein powder, a banana, nut butter, and oats into a single drink can easily reach 500 to 700 calories and goes down faster than a full plate of food.
Why Food Quality Still Matters
It’s tempting to hit a calorie surplus by eating fast food, pizza, and ice cream. This approach, sometimes called “dirty bulking,” does cause weight gain, but the results aren’t what most people want. A study of 600 elite athletes compared those who ate in a large surplus to those who maintained a normal diet. Both groups improved their strength at the same rate and gained the same amount of muscle. The only difference was fat: the overeating group increased their body fat by 15%, while the maintenance group gained just 2%.
Eating a lot of highly processed food during a bulk also raises your risk of vitamin deficiencies, digestive discomfort, low energy, and drops in testosterone. The extra fat gained doesn’t help performance or appearance, and it takes additional time to lose later. A moderate surplus built around whole foods gets you the same muscle growth with far less unnecessary fat.
Adjusting Over Time
Your calorie needs aren’t fixed. As you gain weight, your body burns more energy at rest simply because there’s more of you. A surplus that worked at 150 pounds may become a maintenance intake at 165 pounds. Recalculate your TDEE every 10 to 15 pounds gained and adjust your food intake upward to keep the surplus consistent.
Activity changes matter too. If you start a new training program or increase your workout volume, you’ll burn more calories and may need to eat more to compensate. On rest days, your needs drop slightly, though most people find it simpler to keep intake consistent day to day rather than cycling calories up and down.
If your weight stalls for two or more weeks and you’re confident in your tracking, add 100 to 200 calories per day. Small, gradual increases are easier to sustain and less likely to overshoot into excessive fat gain. Patience is the strategy here: a person gaining half a pound per week puts on 26 pounds in a year, almost all of which can be lean mass with the right training.