To gain weight, you need to eat roughly 300 to 500 calories per day above what your body burns. That surplus provides the extra energy your body needs to build new tissue. The exact number depends on your metabolism, activity level, age, and whether you’re aiming for muscle gain or general weight gain.
Find Your Starting Point
Before you can figure out how many extra calories to eat, you need to know how many calories your body burns in a typical day. This number is called your Total Daily Energy Expenditure, or TDEE. It accounts for three things: the calories your body uses just to keep you alive (breathing, circulating blood, maintaining body temperature), the calories burned through physical activity, and a smaller amount burned digesting food.
The most widely used method starts with the Mifflin-St Jeor formula to estimate your resting calorie burn:
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
You then multiply that number by an activity factor: 1.2 if you’re mostly sedentary, 1.375 if you exercise lightly a couple times a week, 1.55 for moderate activity, 1.725 for intense daily training, and 1.9 for elite-level athletic schedules. The result is a reasonable estimate of the calories you burn each day. Everything you eat beyond that number is your surplus.
For a quick example: a moderately active 30-year-old man who weighs 70 kg (154 lbs) and stands 178 cm (5’10”) would have a resting burn of about 1,648 calories, and a TDEE of roughly 2,555 calories. To gain weight, he’d aim for around 2,900 to 3,050 calories per day.
How Big Your Surplus Should Be
The most common recommendation is to add 500 calories per day above your TDEE. That’s a reasonable target for general weight gain and is easy to remember. But recent evidence suggests a more nuanced range works better for most people: a surplus of 5 to 20% above your maintenance calories.
For someone whose TDEE is 2,000 calories, that translates to an extra 100 to 400 calories per day. If your TDEE is 2,500, the range is 125 to 500 extra calories. Starting at the lower end (around 5 to 10%) and increasing only if you’re not seeing results on the scale after two to three weeks helps you gain weight without packing on unnecessary body fat. People who are very active or already lean may need the higher end of that range, while someone looking to gain weight gradually can start smaller.
Why the “3,500 Calories per Pound” Rule Is Misleading
You’ve probably heard that 3,500 extra calories equals one pound of body weight. While a pound of body fat does contain roughly 3,500 calories of stored energy, the math doesn’t work as cleanly as it sounds. Eating an extra 100 calories a day for 35 days won’t reliably produce exactly one pound of gain.
Your body adapts as you eat more. Your metabolism speeds up slightly, you generate more body heat, and your body may unconsciously increase small movements throughout the day. These compensatory responses mean some of those extra calories get burned off rather than stored. The real-world result is that early weight gain tends to come faster, then slows down as your body adjusts to the higher intake. This is normal and doesn’t mean the surplus has stopped working. It means you may need to bump your intake up slightly every few weeks to keep gaining at a steady pace.
Prioritize Protein for Lean Gains
Calories determine whether you gain weight, but protein determines what kind of weight you gain. Without enough protein and some form of resistance exercise, a calorie surplus tends to add mostly fat. With adequate protein, a much larger share goes toward building muscle.
The target for muscle building is 1 to 1.5 grams of protein per kilogram of body weight per day. For a 70 kg (154 lb) person, that’s 70 to 105 grams daily. Going above that range doesn’t accelerate muscle growth further. The remaining calories in your surplus can come from carbohydrates and fats based on your preferences and what helps you eat consistently.
High-Calorie Foods That Make It Easier
One of the biggest practical challenges of gaining weight is actually eating enough food. If you have a small appetite or feel full quickly, calorie-dense foods let you hit your target without forcing enormous portions. Nuts pack 160 to 200 calories per quarter-cup. A third of an avocado has about 80 calories. An ounce and a half of cheddar cheese delivers around 173 calories. Olive oil, nut butters, seeds, and full-fat dairy are all efficient ways to add calories without adding volume to your plate.
Liquid calories are another practical tool. Research from Cambridge University shows that liquids have a much lower satiating effect than solid foods. Your body is slower to register calories consumed as a drink, so you’re less likely to compensate by eating less at your next meal. In one study, participants who consumed the same number of carbohydrate calories in liquid form ate just as much the rest of the day, while those who consumed the same calories as solid food naturally ate less later. Smoothies made with milk, protein powder, banana, nut butter, and oats can easily deliver 400 to 600 calories and won’t kill your appetite for dinner.
Soup is the interesting exception here. Despite being liquid, soup is consumed at a much slower rate, closer to the pace of solid food. That slower eating rate triggers stronger fullness signals. So if you’re struggling to eat enough, smoothies and shakes work better than soup for getting extra calories in.
Tracking and Adjusting Over Time
Weigh yourself at the same time each day (ideally in the morning, before eating) and look at the weekly average rather than any single reading. Daily weight fluctuates by one to three pounds based on water, salt, and digestion. A reasonable rate of gain for most people is about 0.5 to 1 pound per week. Faster than that, and a large portion of the gain is likely fat rather than muscle.
If the scale isn’t moving after two full weeks, add another 100 to 200 calories per day. If you’re gaining faster than a pound per week and aren’t trying to recover from being underweight, consider pulling the surplus back slightly. Your TDEE isn’t a fixed number. It shifts as your body weight changes, your activity fluctuates, and your metabolism adapts, so expect to make adjustments every few weeks.
When Being Underweight Is the Concern
A BMI below 18.5 is classified as underweight by the CDC. If you fall into that category and have been unable to gain weight despite eating more, underlying causes like thyroid issues, digestive conditions, or medication side effects may be limiting absorption or increasing calorie burn. Unexplained weight loss or an inability to gain weight over several months warrants a medical evaluation, because the solution may involve more than just adding calories.