Hi, Being under or overweight is decided by BMI (Body Mass Index). It depends on your weight and height. You can calculate your BMI using this simple formula: BMI = Body Weight in Kilograms / (height in meter * height in meter) If the answer comes below 18.5, then you surely need to gain some weight as you need more body mass to maintain optimal health. Your BMI is 18.54, which is just the borderline BMI between underweight and normal. However, if you still want to gain weight here are some simple ways that I can advise you to gain weight. Join a gym nearby and start exercising regularly. Do exercises that can help to build muscle mass and gain weight. A gym trainer can teach you those exercises. You can add more proteins in your diet like dairy products and nuts to increase muscle mass. You should have at least 3 meals per day and should include high carbohydrate and fat food in your meals. Having adequate sleep can also help in increasing muscles mass. However, you should take care to gain weight in healthy way and not become obese or unhealthy. Avoid drinking too much sodas. Do not overeat at any one time. I hope this information helps. Thank you for choosing HealthcareMagic. Best, Dr. Viraj Shah