Weight Gain Calculator
Enter your stats and target weight to find your daily calorie goal for steady, healthy weight gain. The calculator uses the Mifflin-St Jeor equation to find your maintenance calories, then adds a surplus matched to your chosen pace. You also get your recommended protein, carbohydrate, and fat targets, plus a week-by-week schedule showing exactly when you will reach your goal. Switch between metric and imperial units at any time.
How to use this calculator
Fill in your sex, age, height, current weight, and target weight, then choose your activity level and preferred pace. The calculator estimates your Total Daily Energy Expenditure (TDEE) using the Mifflin-St Jeor equation, adds the calorie surplus for your chosen pace, and outputs your daily calorie goal, a macro breakdown, and a week-by-week schedule showing how your weight should progress. Update the numbers every 2 to 4 weeks as your weight changes, because your TDEE rises alongside your bodyweight and your calorie target needs to follow it.
The formula: Mifflin-St Jeor and the calorie surplus
The Mifflin-St Jeor equation calculates your Basal Metabolic Rate (BMR), the calories your body burns at complete rest. For men: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age (years) + 5. For women: the same formula but -161 instead of +5. Your TDEE is BMR multiplied by an activity factor that ranges from 1.2 (sedentary) to 2.1 (twice-daily training). The daily calorie surplus required to gain approximately 1 kg of bodyweight is around 7,700 kcal (3,500 kcal per pound). A +250 kcal/day surplus therefore produces roughly 0.23 kg/week of gain, +350 kcal produces 0.32 kg/week, and +500 kcal produces 0.45 kg/week.
Protein, carbohydrates, and fat for weight gain
Hitting your calorie target is necessary, but what you eat matters nearly as much as how much. Protein is the most important macro for gaining lean mass: 1.6 to 2.2 g per kg of bodyweight per day is the evidence-based range, and this calculator targets 1.8 g/kg. Carbohydrates fuel your training sessions and replenish muscle glycogen, and they should make up the bulk of calories beyond protein. Fat is kept at about 25% of total calories, which supports hormone production and micronutrient absorption. The macro targets update live with your weight and calorie goal.
Why weight gain stalls, and how to fix it
The most common reason a weight gain plan fails is underestimating calorie intake, which is very easy when eating out or estimating portion sizes. A second culprit is overestimating activity: people who train hard for 1 hour but sit for the other 15 waking hours are closer to "moderate" than "very active." If your weight has not changed after 2 weeks on your calculated intake, add 100 to 200 kcal/day and wait another week before adjusting again. Track everything for at least 3 to 5 days before concluding you are in a surplus, because daily weight fluctuates by 1 to 3 kg due to water, food, and sodium intake.
Weight gain pace comparison
| Pace | Daily surplus | Weekly gain | Fat:muscle ratio | Best for |
|---|---|---|---|---|
| Lean Bulk | +250 kcal | ~0.23 kg (0.5 lb) | Mostly muscle | Beginners, re-composition |
| Moderate Gain | +350 kcal | ~0.32 kg (0.7 lb) | Good balance | Most natural lifters |
| Aggressive Gain | +500 kcal | ~0.45 kg (1 lb) | More fat included | Underweight, hard gainers |
Choosing the right surplus depends on your training experience, body composition goals, and how quickly you want to gain. The figures assume a 70 kg starting weight.
Frequently asked questions
How many calories should I eat to gain weight?
You need to eat more calories than your body burns each day. First calculate your Total Daily Energy Expenditure (TDEE), then add a surplus of 250 to 500 kcal/day depending on how fast you want to gain. A 250 kcal surplus produces about 0.25 kg (0.5 lb) of gain per week; a 500 kcal surplus produces about 0.5 kg (1 lb) per week. This calculator works both figures out for you automatically.
What is the Mifflin-St Jeor equation?
Mifflin-St Jeor is the most widely validated formula for estimating Basal Metabolic Rate (BMR), the calories you burn at complete rest. For men: BMR = 10W + 6.25H - 5A + 5. For women: BMR = 10W + 6.25H - 5A - 161, where W is weight in kg, H is height in cm, and A is age in years. Multiplying the BMR by an activity factor (1.2 to 2.1) gives your TDEE.
What is a lean bulk and is it better than a regular bulk?
A lean bulk uses a smaller calorie surplus (around 250 kcal/day) to gain weight slowly, keeping most of the gain as muscle and minimising fat storage. It is best for people who are already at a normal body fat percentage and want to stay lean. A larger surplus (aggressive bulk) gains mass faster but includes more fat, which must be dieted off later. Most natural lifters do best with a moderate surplus of 250 to 350 kcal/day.
How much protein do I need to gain muscle?
The evidence-based range for maximising muscle protein synthesis is 1.6 to 2.2 g of protein per kg of bodyweight per day. This calculator uses 1.8 g/kg as a practical target. For a 70 kg person that is about 126 g/day. Spread your protein across 3 to 5 meals to maximise absorption, and prioritise complete protein sources such as eggs, meat, fish, dairy, and soy.
Why is my weight not going up even though I am eating more?
The most common causes are: underestimating portion sizes (use a food scale for at least the first few weeks), overestimating your activity level, or not eating consistently enough on rest days. Daily weight also fluctuates by 1 to 3 kg due to water retention, food volume, and sodium, so weigh yourself in the morning after using the bathroom and compare weekly averages rather than daily readings.
How often should I recalculate my calorie goal?
Recalculate every 2 to 4 weeks. As your bodyweight increases, your TDEE rises too (because a heavier body burns more calories), so your calorie target needs to increase to maintain the same rate of gain. A rough rule of thumb is an extra 10 kcal/day for each kilogram of bodyweight gained.
Can I gain weight without exercise?
Yes, but without resistance training the extra calories are stored mostly as fat rather than muscle. To gain functional, lean mass, combine the calorie surplus with progressive resistance training (weightlifting, bodyweight exercises) at least 3 days per week. Training also increases your TDEE, which means you can eat more while still staying in a controlled surplus.
Sources
- Mifflin MD et al. (1990), A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition.
- Morton RW et al. (2018), A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength. British Journal of Sports Medicine.