[header] How to gain weight fast (for women ) [title] Consume an additional 500 calories per day. [step] It is generally safe to gain 1-2 pounds (0.45-0.91 kg) per week. To reach this goal, add an extra 500 calories to your diet everyday. 
The healthiest way to do this is to eat more nutrient-dense foods. [substeps] To keep track of what you're eating, use a health app, such as myfitnesspal.