To gain weight, you need to consistently eat more calories than your body burns and pair that surplus with resistance training to ensure most of the gain is muscle rather than fat. It takes roughly 2,000 to 2,500 extra calories per week to build a pound of lean muscle, which works out to about 300 to 350 extra calories per day above what you need to maintain your current weight.
How Big Your Calorie Surplus Should Be
A pound of fat requires about 3,500 excess calories per week to accumulate, while a pound of muscle requires closer to 2,000 to 2,500. That difference matters. If you eat 700 or 800 extra calories a day hoping for faster results, most of the additional gain will be fat. A moderate surplus of 300 to 500 calories daily is the sweet spot for gaining weight at a healthy pace.
A reasonable target is gaining 0.25% to 0.5% of your body weight per week. For someone who weighs 150 pounds, that’s roughly 0.4 to 0.75 pounds per week. Weigh yourself once a week at the same time of day and track the trend over several weeks rather than reacting to daily fluctuations, which mostly reflect water and food volume.
What to Eat (and How Much Protein)
Protein is the single most important macronutrient for turning a calorie surplus into muscle. Aim for 1.6 to 2.2 grams of protein per kilogram of body weight each day. For a 70-kilogram (154-pound) person, that’s 112 to 154 grams of protein spread across the day. Beyond that range, extra protein doesn’t appear to further boost muscle growth, so you’re better off filling remaining calories with carbohydrates and healthy fats.
Carbohydrates fuel your workouts and help with recovery. Fats are calorie-dense at 9 calories per gram (compared to 4 for protein and carbs), which makes them especially useful when you’re struggling to eat enough. A practical split for gaining weight is roughly 25 to 35% of calories from protein, 40 to 50% from carbohydrates, and 20 to 30% from fat, but the exact ratios matter less than hitting your total calorie and protein targets consistently.
Calorie-Dense Foods That Make It Easier
If you’re someone with a small appetite, trying to gain weight on chicken breast and steamed vegetables is going to feel impossible. Calorie-dense foods let you pack more energy into smaller volumes. Some of the most useful options:
- Nuts and nut butters: A quarter cup of most nuts delivers 160 to 200 calories. Two tablespoons of peanut butter on toast adds roughly 190 calories and 7 grams of protein with minimal effort.
- Cheese: An ounce and a half of sharp cheddar has 173 calories and 10 grams of protein. Swiss cheese is similar at 167 calories. Grate it over meals, add it to eggs, or eat it as a snack.
- Avocado: One-third of an avocado has about 80 calories, so a full avocado adds around 240 calories to a meal.
- Whole grains: Rice, oats, and granola are cheap, easy to prepare in bulk, and calorie-dense compared to most other carb sources.
- Olive oil and butter: A tablespoon of olive oil drizzled over a dish adds about 120 calories without changing the portion size.
Why Smoothies and Shakes Help
Liquid calories are one of the most effective tools for weight gain because they don’t fill you up the way solid food does. A homemade shake with whole milk, a banana, two tablespoons of peanut butter, a scoop of protein powder, and a handful of oats can easily reach 600 to 800 calories. You can drink it between meals without suppressing your appetite for the next one.
UCSF Health recommends adding ingredients like silken tofu (for protein without changing the flavor), yogurt, pre-cooked oats or rice, and even ice cream to boost the calorie content of shakes. If you find yourself falling short on your daily target by dinner, a shake before bed is an easy way to close the gap.
Meal Frequency Is About Convenience, Not Magic
You’ll often hear that eating five or six small meals a day is better for gaining weight. Research doesn’t support this as a metabolic advantage. A systematic review of randomized controlled trials found that meal frequency had no significant effect on total energy intake. The real benefit of eating more often is practical: if you struggle to eat large meals, splitting your food into four or five smaller sittings can make it easier to reach your calorie goal. But if you prefer three bigger meals and a shake, that works just as well.
Resistance Training Turns Calories Into Muscle
Eating in a surplus without training will add weight, but a large portion of it will be fat. Resistance training sends the signal your body needs to direct those extra calories toward building muscle tissue. For beginners, training two to three days per week with a full-body routine is enough to stimulate growth. After about six months, moving to four sessions per week with an upper/lower body split becomes more effective. More advanced lifters may train four to six days per week, focusing on one to three muscle groups per session.
Interestingly, research reviews have found that training a muscle group once per week produces similar growth to training it two or three times per week, as long as the total weekly training volume is the same. So the key variable isn’t how often you train a muscle each week. It’s how many hard sets you accumulate for that muscle over the course of a week. For most people, 10 to 20 challenging sets per muscle group per week is a solid range for growth.
Focus on compound movements like squats, deadlifts, bench presses, rows, and overhead presses. These recruit the most muscle mass per exercise, give you the most return on your time, and allow you to progressively increase the weight over months.
Why You Might Not Be Gaining
The most common reason people fail to gain weight is simply not eating as much as they think. Tracking your food with an app for even one or two weeks often reveals a gap between what you believe you’re eating and what you’re actually consuming. Many people who describe themselves as “hard gainers” find they’re eating 1,800 to 2,200 calories on days they thought they were eating 3,000.
Certain medical conditions can also make gaining weight harder. An overactive thyroid speeds up your metabolism significantly. Digestive conditions like celiac disease or Crohn’s disease can reduce how many calories your body actually absorbs from food. Type 1 diabetes, chronic infections, and some medications (particularly stimulants prescribed for ADHD) can suppress appetite or increase calorie expenditure. If you’re eating in a consistent surplus, training regularly, and still not gaining weight after several weeks, it’s worth having bloodwork done to rule out an underlying issue.
A Simple Starting Framework
Calculate your rough maintenance calories using an online calculator based on your age, sex, height, weight, and activity level. Add 300 to 500 calories to that number. Hit at least 1.6 grams of protein per kilogram of body weight. Lift weights two to four times a week. Weigh yourself weekly and adjust: if you’re not gaining after two weeks, add another 200 calories per day. If you’re gaining faster than 0.5% of your body weight per week and the extra is clearly fat, scale back slightly.
Consistency matters far more than perfection. Missing your calorie target one day won’t derail you, but regularly falling 300 to 400 calories short will keep you at the same weight for months. Building the habit of eating enough is, for most underweight people, harder than the training itself.