Quick answer
Daily calorie surplus = weekly gain (kg) × 7,700 ÷ 7. Gaining 0.25 kg a week from a 2,400 kcal maintenance needs a 275 kcal surplus, for 2,675 kcal a day.
Enter the weekly gain and your maintenance calories. The calculator returns the surplus and the target intake. Use this weight gain calculator to check your own figures.
Related tools: Weight Loss Percentage Calculator: Percentage of starting weight lost.
How to use the Weight Gain Calculator
- Choose units: Metric (kg, cm) and Imperial (lb, in).
- Enter gain per week (kg, or lb) (above 0).
- Optionally, enter maintenance calories (optional) (kcal/day) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Units | Choose one: Metric (kg, cm); Imperial (lb, in) | Starts at Metric (kg, cm) |
| Gain per week (kg, or lb) | A number | > 0 |
| Maintenance calories (optional) (optional) | A number, in kcal/day | > 0 |
Formula and method
Formula
daily surplus = weekly gain (kg) × 7,700 ÷ 7
IEEE-754 double precision; shown to the decimals indicated.
Uses the common approximation of about 7,700 kcal per kg; part of any gain is lean mass depending on training. Informational estimate, not medical advice. Talk to a qualified health professional about your own situation.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Units = Metric (kg, cm); Gain per week (kg, or lb) = 0.25; Maintenance calories (optional) = 2400.
| Result | Value |
|---|---|
| Daily calorie surplus | 275 |
| Daily calorie target | 2,675 |
Example 2
Inputs: Units = Imperial (lb, in); Gain per week (kg, or lb) = 1.
| Result | Value |
|---|---|
| Daily calorie surplus | 499 |
| Daily calorie target | — |
Example 3
Inputs: Units = Metric (kg, cm); Gain per week (kg, or lb) = 0.5; Maintenance calories (optional) = 2800.
| Result | Value |
|---|---|
| Daily calorie surplus | 550 |
| Daily calorie target | 3,350 |
The first line is the headline result (daily calorie surplus). Below it the weight Gain Calculator lists daily calorie target, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
The arithmetic
0.25 × 7,700 = 1,925 kcal a week, ÷ 7 = 275 kcal a day. A gain faster than about 0.5 kg a week is mostly fat, so slow gradual gain with strength training favours muscle.
Approximation
7,700 kcal per kg is a rule of thumb; real gain depends on activity, hormones and body composition. Adjust every few weeks according to the scale. Consult a professional if underweight for medical reasons.
How the result changes with gain per week
Holding every other input at the first worked example, this table changes only gain per week. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Gain per week | Daily calorie surplus | Daily calorie target |
|---|---|---|
| 0.125 | 138 | 2,538 |
| 0.25 | 275 | 2,675 |
| 0.5 | 550 | 2,950 |
| 1 | 1,100 | 3,500 |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Gain per week (kg, or lb): entering "0" shows "Gain per week (kg, or lb) must be greater than 0." beside that field and no result.
Choosing between the Weight Gain Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Weight Loss Calculator](/health/weight-loss-calculator/) | units, current weight and goal weight | Days to reach goal |
| [Pregnancy Weight Gain Calculator](/health/pregnancy-weight-gain-calculator/) | units, pre-pregnancy weight and height | Recommended total gain |
| [Weight Loss Percentage Calculator](/health/weight-loss-percentage/) | starting weight and current weight | Weight lost |
| [Weight Change Rate Calculator](/health/weight-change-rate-calculator/) | units, starting weight and ending weight | Change per week |
| [Calorie Deficit Calculator](/health/calorie-deficit-calculator/) | units, weight to lose and time | Daily calorie deficit |
Background: body measurements and screening
Body-measurement ratios are screening tools, not diagnoses. BMI ignores body composition and fat distribution, and reviews find waist-to-hip and waist-to-height ratios are useful additions but not clearly better than BMI or waist circumference alone. Where the tape goes matters, so measure at the same sites each time.
Some sources quote a waist-to-hip ratio above 0.8 for women and 0.95 for men as a marker of increased metabolic risk; treat that as a screening flag, and talk to a clinician about what your own numbers mean.
Assumptions and limitations
- Gain faster than about 0.5 kg a week is mostly fat
- Not a diagnosis
This calculator gives general information based on published formulas. It is not medical advice, and it cannot account for your health history. Talk to a qualified clinician about decisions that affect your health.
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for gain per week (kg, or lb) to confirm this.
Frequently asked questions
How do I gain muscle not fat?
Modest surplus plus resistance training.
How much protein?
1.6 to 2.2 g per kg is common.
What is maintenance?
Calories to keep weight steady.
What does the Weight Gain Calculator calculate?
Daily calorie surplus for a target weekly weight gain. It returns Daily calorie surplus and Daily calorie target.
What formula does the Weight Gain Calculator use?
daily surplus = weekly gain (kg) × 7,700 ÷ 7. Uses the common approximation of about 7,700 kcal per kg; part of any gain is lean mass depending on training.
What do I need to enter in the weight Gain Calculator?
You enter Units and Gain per week (kg, or lb). Optional: Maintenance calories (optional) (kcal/day).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Gain faster than about 0.5 kg a week is mostly fat.
What are the limits of this calculator?
Gain faster than about 0.5 kg a week is mostly fat. Not a diagnosis.
What does the “Units” option change?
It sets how the weight Gain is worked out. The choices are Metric (kg, cm) and Imperial (lb, in).
What is an example of a weight Gain result?
With units Metric (kg, cm), gain per week (kg, or lb) 0.25 and maintenance calories (optional) 2400, the daily calorie surplus is 275.
Where does the method come from?
The method follows: Wishnofsky M, Am J Clin Nutr 1958;6:542 (approximation).
Can I rely on this calculator for a decision?
This calculator gives general information based on published formulas. It is not medical advice, and it cannot account for your health history. Talk to a qualified clinician about decisions that affect your health. For this calculator in particular: Gain faster than about 0.5 kg a week is mostly fat.
Related calculators
- Weight Loss Percentage Calculator — Percentage of starting weight lost.
- Weight Change Rate Calculator — Average weight change per week and as a share of starting weight.
- Ideal Weight Calculator — Ideal body weight by four published formulas (Devine, Robinson, Miller, Hamwi).
Sources
- Wishnofsky M, Am J Clin Nutr 1958;6:542 (approximation)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.