Gaining weight in a healthy way is a challenge for many lean adults who struggle to add muscle. The concept of energy balance—the relationship between calories consumed and calories burned—sits at the heart of the process. This guide pulls together official recommendations from the Dietary Guidelines for Americans, the National Health Service (NHS), and the U.S. Department of Health and Human Services (HHS) to help you understand how to manage intake and activity for gradual, sustainable weight gain. It is designed for individuals who find it hard to gain muscle, often described as hard gainers or ectomorphs, but remember that body type is a description, not a diagnosis or a limit on what you can achieve. This article is part of our nutrition for muscle gain section.

Short version: To gain weight, you need a calorie surplus. The NHS suggests adding 300 to 500 extra calories a day through smaller, more frequent meals and nutrient-dense snacks. Keep physical activity, both aerobic and strength training, as recommended by the HHS, because it supports muscle growth and overall health. If you have unexplained weight loss or a medical condition, speak with a doctor first.

Understanding Energy Balance

According to the Dietary Guidelines for Americans, the total number of calories a person needs each day depends on age, sex, height, weight, and level of physical activity. Energy balance is the state where calories consumed equal calories expended. To gain weight, you need a positive energy balance—consuming more calories than your body uses. The Guidelines note that a need to lose, maintain, or gain weight affects how many calories should be consumed. However, the quality of those calories matters just as much as the quantity. The Dietary Guidelines emphasize following a healthy dietary pattern that focuses on nutrient-dense foods and beverages, staying within calorie limits, and limiting added sugars, saturated fat, and sodium.

Estimated Calorie Needs for Adults

The Dietary Guidelines for Americans provide estimated calorie needs based on reference heights and weights. For adult males, the reference man is 5 feet 10 inches tall and weighs 154 pounds; for adult females, the reference woman is 5 feet 4 inches tall and weighs 126 pounds. Using these references, estimated daily calorie needs range from 2,000 to 3,000 calories for males and 1,600 to 2,400 calories for females, depending on age and physical activity level. Males generally require more calories than females, and calorie needs generally decrease for adults as they age due to reductions in basal metabolic rate. These numbers are only estimates. The Guidelines point to online tools such as the DRI Calculator for Healthcare Professionals, available at nal.usda.gov/fnic/dri-calculator, to estimate individual calorie needs based on personal characteristics and activity level.

Practical Tips to Increase Calorie Intake

The NHS offers straightforward advice for healthy weight gain. Their recommendations focus on adding calories gradually through nutrient-rich foods rather than relying on sugary or fatty snacks. Here are the key do’s and don’ts, as stated by the NHS:

  • Gain weight gradually by adding healthy calories. Adults could try adding around 300 to 500 extra calories a day.
  • Eat smaller meals more often, and add healthy snacks between meals.
  • Add extra calories to meals with cheese, nuts, and seeds.
  • Have high-calorie drinks in between meals, such as milkshakes.
  • Follow a balanced diet that includes a variety of food groups: fruit and vegetables, starchy carbohydrates, dairy and alternatives, and protein foods.
  • Add protein to meals with beans, pulses, fish, eggs, and lean meat.
  • Choose snacks that are easy to prepare, such as yogurt or rice pudding.
  • Build muscle with strength training or yoga—exercise can also improve your appetite.
  • Do not rely on chocolate, cakes, and sugary drinks to gain weight.
  • Do not fill up on drinks before eating meals.

The NHS also reminds individuals that being underweight could mean missing out on vitamins and minerals, which may lead to health problems such as a weak immune system and bone fractures. For more on planning meals that support muscle gain, see our calorie intake guide and protein basics for strength training.

Keeping Physical Activity in the Equation

Some people trying to gain weight consider cutting back on physical activity to reduce calorie expenditure. However, the HHS Physical Activity Guidelines for Americans make clear that regular physical activity provides substantial health benefits, including improved cardiorespiratory and muscular fitness, healthier body weight and body composition, and better ability to perform everyday tasks. The key is to balance activity with adequate calorie intake, not to eliminate it.

The HHS recommends that adults do at least 150 minutes to 300 minutes of moderate-intensity aerobic activity per week, or 75 minutes to 150 minutes of vigorous-intensity aerobic activity, or an equivalent combination. Aerobic activity should preferably be spread throughout the week. In addition, adults should do muscle-strengthening activities of moderate or greater intensity that involve all major muscle groups on 2 or more days a week. Muscle-strengthening activities, such as lifting weights, working with resistance bands, or doing body-weight exercises, overload the muscles and support increases in muscle strength and mass. The HHS notes that when resistance training is used to enhance muscle strength, one set of 8 to 12 repetitions of each exercise is effective, although 2 or 3 sets may be more effective. Improvements are progressive over time, so gradually increasing the amount of weight or the days of exercise will lead to stronger muscles.

To gauge intensity, the HHS offers the talk test: a person doing moderate-intensity activity can talk but not sing, while a person doing vigorous-intensity activity cannot say more than a few words without pausing for a breath. Even light-intensity activity is beneficial, and the biggest health gains come from moving from no activity to some activity. The Guidelines stress that “some is better than none” and that adults should move more and sit less throughout the day.

For structured strength-training plans, explore our beginner strength training resources. Adequate rest and recovery are also essential for muscle growth. For more on how recovery supports strength progress, see our rest and recovery guide.

When to Talk to a Healthcare Professional

The NHS advises speaking to a GP if you have lost weight suddenly, lost weight without changing your diet or exercise routine, or if you use control of food to cope with feelings and other situations. These could be signs of an underlying health condition. Additionally, anyone with a medical condition, a history of injury, an eating disorder, or who is underweight should consult a doctor or registered dietitian before making significant changes to diet or exercise. A healthcare provider can help rule out medical causes of low appetite or unintended weight loss and offer personalized guidance.

Frequently asked questions

How many extra calories do I need to gain weight?

The NHS suggests that adults trying to gain weight could start by adding around 300 to 500 extra calories a day, doing so gradually. The exact number depends on your individual energy needs, which are influenced by age, sex, height, weight, and activity level. The Dietary Guidelines for Americans provide estimated calorie ranges and point to tools like the DRI Calculator for a more personalized estimate.

Should I stop doing cardio if I’m trying to gain weight?

No. The HHS Physical Activity Guidelines recommend that all adults get regular aerobic activity for substantial health benefits, including lower risk of chronic diseases and improved body composition. Instead of cutting out cardio, adjust your calorie intake to support both your activity and weight gain goals. Combining aerobic exercise with muscle-strengthening activities can help you build a stronger, healthier body.

What if I eat more and still can’t gain weight?

The Dietary Guidelines say calorie needs depend on age, sex, height, weight and physical activity, so your needs may sit above the published estimates. If you consistently struggle to gain weight despite following a calorie surplus and strength training, consider speaking with a registered dietitian who can assess your overall diet and energy expenditure. Unintended weight loss or difficulty gaining may sometimes signal an underlying issue, so a medical check-up is also wise.

For more on energy balance and muscle gain nutrition, visit our Energy Balance category page.

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