Weight Gain Calculator

To gain weight, eat above your maintenance calories (TDEE). A weight gain calculator estimates that maintenance level and adds a surplus: about 250 calories a day for roughly 0.5 lb a week or 500 a day for roughly 1 lb a week. Example: a moderately active 22-year-old man, 5 ft 10 in and 150 lb, has a TDEE of about 2,614 calories, so he eats about 3,114 calories a day to gain about 1 lb a week. Expect the pace to slow over months as your maintenance rises.

This is a dedicated gaining tool. The Calorie Calculator shows maintenance, loss and gain in one view, the TDEE Calculator and BMR Calculator give your burn alone, and the BMI Calculator shows where your current and goal weights fall.

How the surplus is calculated

The tool works in two steps. First it estimates your maintenance calories (TDEE) from the Mifflin-St Jeor equation for basal metabolic rate (BMR):

where s is +5 for men and −161 for women. BMR is multiplied by an activity factor (1.2 sedentary to 1.9 extra active, a convention rather than part of the equation) to get TDEE. Your daily target is then:

By the common rule that about 3,500 calories equals a pound of body weight, a 250-calorie daily surplus (1,750 a week) adds about half a pound a week and 500 a day (3,500 a week) about a pound. NIH researchers have shown that body weight responds to a lasting change in intake only gradually, with a half-time of about a year (Hall et al., 2011), so a fixed surplus produces a gain that slows over time. The free NIH Body Weight Planner models that slowdown.

Calorie surplus to weekly and monthly weight gain

This quick reference converts a daily surplus into a pace using the 3,500-calorie rule. Larger surpluses gain faster but with a bigger share of fat.

Monthly gain = weekly gain × 52 ÷ 12. These are planning numbers from the 3,500-calorie rule; real gains usually taper.

A worked example

Suppose you are a 30-year-old woman, 5 ft 5 in and 120 lb, lightly active, aiming for 135 lb. Your BMR is about 1,265 calories; at an activity factor of 1.375 your TDEE is about 1,740 calories. On the standard +500 surplus your target is about 2,240 calories a day, roughly 1 lb a week by the 3,500-calorie rule. To add the 15 lb between 120 and 135, the calculator estimates 15 weeks (about 3.5 months); in practice it will likely take a little longer as your maintenance rises. The leaner +250 pace takes about 30 weeks for the same 15 lb, with less fat gain.

How many calories to gain weight, by body profile

Daily calorie targets from the Mifflin-St Jeor equation for five profiles at three surplus sizes, rounded to the nearest 10 calories.

The calculator shows unrounded values (for example 2,614 and 3,114 for the 22-year-old man). Treat these as starting points.

How long to gain 10, 20 or 30 pounds

Weeks to reach a goal at each pace by the 3,500-calorie rule, rounded up to whole weeks as in the calculator. A +250 surplus is about 0.5 lb a week, +500 about 1 lb and +750 about 1.5 lb.

How big should the surplus be?

A 2019 review of nutrition for natural bodybuilders recommends eating about 10% to 20% above maintenance and aiming to gain about 0.25% to 0.5% of body weight per week for novice and intermediate lifters, with experienced lifters at the lower end (Iraki et al.). For the 150 lb man in the intro, 10% to 20% of his 2,614-calorie maintenance is about 261 to 523 calories, which matches the lean and standard paces, and 0.25% to 0.5% of his weight is about 0.4 to 0.75 lb a week. The same review describes a study of elite athletes in which a group eating about 600 calories more per day gained significantly more fat (1.1 kg vs 0.2 kg) without a significant difference in lean mass; the researchers suggested 200 to 300 extra calories for highly trained athletes.

How to use this calculator

1. Pick your units: US (lb, ft/in) or metric (kg, cm); switching converts your entries.
2. Enter your stats: sex, age, height and current weight feed the BMR equation.
3. Set your goal weight: it must be higher than your current weight to show a timeline.
4. Choose an activity level: overstating activity inflates your target.
5. Pick a pace: lean (+250), standard (+500), or a custom weekly rate in lb or kg.
6. Read the result: your daily calorie target, plus BMR, TDEE, surplus, protein and weeks to your goal.

Who this calculator is for

• Hardgainers who struggle to put on size and want a concrete daily number.
• Lifters bulking who want to add muscle with a controlled surplus.
• People regaining weight after illness, injury or unintended loss, ideally with their doctor.
• Athletes adding mass for a sport or weight class.

Key terms explained

• BMR: basal metabolic rate, the calories you burn at complete rest.
• TDEE: total daily energy expenditure, BMR plus everything you do in a day; your maintenance level.
• Surplus: calories eaten above maintenance.
• Lean bulk: a small surplus that aims for muscle with limited fat gain.
• Recomposition: gaining muscle while losing fat at the same time.

Three pace scenarios

Using the 2,614-calorie maintenance from the intro example:

• Lean (+250 a day): about 2,864 calories a day, about 0.5 lb a week.
• Standard (+500 a day): about 3,114 calories a day, about 1 lb a week.
• Faster (+750 a day): about 3,364 calories a day, about 1.5 lb a week, with a larger share of fat.

Factors that change your real number

• Activity level: the biggest swing in TDEE; by the multipliers, sedentary (1.2) and extra active (1.9) differ by 70% of BMR.
• Everyday movement: walking, standing and fidgeting can rise when you eat more, eating into the surplus.
• Training: resistance training directs more of the surplus into muscle.
• Tracking accuracy: label and restaurant calorie counts are estimates.
• Body size: as you gain, your maintenance rises, shrinking a fixed surplus.

Tips for gaining weight well

• Eat calorie-dense foods: nuts, nut butters, olive oil, whole milk, oats, rice and dried fruit add calories without much volume.
• Drink some calories: milk and homemade shakes are easy when appetite is low.
• Hit your protein: about 1.6 to 2.2 g per kg (0.73 to 1.0 g per lb) is the range research supports for muscle gain.
• Lift weights: progressive resistance training turns a surplus into muscle.
• Adjust monthly: if the scale stalls for 2 to 3 weeks, add 150 to 250 calories and recheck.

A second worked example: a hardgainer bulking

A 22-year-old man who is 6 ft 0 in and 145 lb trains hard four days a week and cannot seem to gain. His BMR is about 1,696 calories, and at a "very active" factor of 1.725 his TDEE is about 2,925 calories. On the standard +500 surplus his target is about 3,425 calories for roughly 1 lb a week. Going from 145 to 165 lb, a 20 lb gain, the calculator estimates about 20 weeks, about five months on the 3,500-calorie rule. That is a lot of food for a lean, active man with a small appetite, which is why hardgainers usually struggle with intake rather than math. Splitting the target across four or five meals plus a calorie-dense shake makes it easier; if the scale has not moved after three weeks, the fix is almost always to eat more.

Building your meals around the surplus

• Anchor each meal with protein: chicken, beef, eggs, fish, Greek yogurt, tofu or a protein shake. The Protein Calculator turns your weight into a daily gram target.
• Lean on calorie-dense foods: nuts, nut butters, olive oil, whole milk, cheese, oats, rice, pasta, potatoes, avocado and dried fruit.
• Add, don't replace: a glass of milk, a handful of nuts or an extra spoon of oil on top of normal meals often covers the surplus.
• Split the load: four or five smaller meals are easier to finish than three big ones.

To turn the target into protein, carb and fat grams, use the Macro Calculator.

Turning the surplus into muscle, not just fat

A surplus guarantees weight gain but not what kind. Three levers decide the mix: surplus size, protein and resistance training. A 2018 meta-analysis of 49 trials found that extra protein stopped adding to strength-training muscle gains at about 1.6 g per kg of body weight a day, with an upper estimate near 2.2 g/kg (Morton et al.). Progressive overload, adding weight, reps or sets over time, is the training signal that tells your body to use the extra calories for muscle. The scale cannot tell muscle from fat, so track strength, tape measurements and photos too; the Body Fat Calculator gives a rough body fat estimate.

Why the scale stalls, and how to fix it

• You are not actually in a surplus. Calorie counts are estimates; track honestly for a week to find the gap.
• Your maintenance rose. As you gain, TDEE climbs; re-enter your current weight and recalculate.
• You move more. Everyday activity can rise when you eat more and quietly burn part of the surplus.
• Daily weight is noisy. Water, sodium and meals swing the scale; compare weekly averages.

The practical rule: if your weekly average has not moved in two to three weeks, add 150 to 250 calories a day and check again.

Special situations: women, teens and older adults

• Women generally have lower BMRs than men of the same height and weight (the equation's sex term is −161 versus +5), so smaller targets are expected.
• Teenagers are still growing; the Mifflin-St Jeor equation was developed in adults, so a pediatrician or sports dietitian should guide a teen's plan.
• Older adults often benefit from putting protein and resistance training first, so that regained weight is muscle rather than fat.
• People recovering from illness or injury may need medical guidance on calories and protein.

Underweight, BMI, and when to see a professional

For adults, the CDC classes a BMI under 18.5 as underweight and 18.5 to under 25 as a healthy weight. This calculator estimates the calories for a chosen rate of gain; it does not judge whether a goal weight is right for you. If you are significantly underweight, losing weight without trying, or have a history of disordered eating, involve a doctor or registered dietitian. The BMI Calculator and Ideal Weight Calculator give quick reference points.

Limitations and assumptions

• The 3,500-calories-per-pound rule overstates gain over months because maintenance rises as weight rises (Hall et al., 2011).
• Mifflin-St Jeor is the equation most likely to land within 10% of measured resting metabolism (Frankenfield et al., 2005), but individuals can be further off.
• The activity multipliers are a convention, not measured values.
• It does not account for medical conditions, medications, pregnancy or eating disorders.
• It estimates total weight, not body composition.

How it compares to related calculators

• For maintenance, loss and gain targets in one view, use the Calorie Calculator.
• For your maintenance number alone, use the TDEE Calculator or Maintenance Calorie Calculator.
• To split your target into protein, carbs and fat, use the Macro Calculator and Protein Calculator.
• To lose instead of gain, use the Weight Loss Calculator.

Sources

• Hall KD et al. (2011), Quantification of the effect of energy imbalance on bodyweight: PubMed 21872751; National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK): Body Weight Planner.
• Iraki J et al. (2019), Nutrition recommendations for bodybuilders in the off-season: PMC6680710.
• Morton RW et al. (2018), protein and resistance training meta-analysis: PubMed 28698222.
• Mifflin MD, St Jeor ST et al. (1990): PubMed 2305711; Frankenfield D et al. (2005): PubMed 15883556.
• Centers for Disease Control and Prevention (CDC): Adult BMI Categories.