Check your current weight
First things first, you need to determine your current weight. Use a weighing machine for this purpose if you own one. If you do not have one at home, it is strongly recommended to purchase one, as it you will find yourself using it regularly. Be sure to check it for zero error as that causes the machine to give an incorrect reading of your weight. It is strongly advised to check your weight early in the morning.
Determine your ideal body weight
You need to determine your ideal body weight. This can be done by calculating your body mass index (BMI) and then using an ideal body weight chart to analyse it. In order to calculate your BMI, you will need to divide your weight in pounds by the square of your height in inches, which can be calculated by using a measuring tape. Multiply the answer by 703 to get your BMI.
Difference between your current and ideal body weight
Subtract the ideal body weight for a person of your body type from your current weight to get the difference. This will give you an idea about the amount of weight that you need to gain and will help you in setting a goal.
Set a realistic goal
With your target weight in mind, decide the number of weeks or months in which you want to reach that target. Do not get too carried away and aim for a high target in very little time as such an approach may end up putting your health and fitness at risk. Take it slowly and steadily instead of rushing it.
Your daily calorie intake
You will need to consult a calorie chart, which can be found using a popular search engine such as Google. Try to remember the foods that you normally eat every day and check the amount of calories in them.
Calories you burn during your running workout
Depending on your current weight, the pace at which you run and the period of your running session, estimate the amount of calories that you burn on average every day. Use the Google search engine to research how much calories are burnt by a person of your weight at a specified pace.
Increase calorie intake accordingly
Consuming 3500 calories adds one pound to your weight. Keeping that in mind, increase the amount of calories you eat accordingly. If you are burning 500 calories in your daily running routine, start consuming 1000 more calories than usual. If you want to gain weight faster, increase your calorie intake even more.