What is calculated
A calorie target, weekly energy surplus, and linear timeline equivalent from an entered maintenance estimate and selected surplus.
Weight Gain Calculator
Daily calorie target for a selected surplus
Enter your values, then calculate to see a verified result.
Reference range
How this result is calculated
A clear calculation path based on your inputs.
Inputs usedReview the information used for this result.
Full calculation and sourcesReview the equation, normalized inputs, assumptions, and version.
Versioned calculationFormula v1.0.0
Method
Add the surplus to maintenance; use 7,700 kcal/kg only as transparent linear arithmetic, not a body-composition forecast.
Important boundary
Actual weight gain is not linear and the calculator does not predict how much gain will be muscle, fat, water, glycogen, or gut contents.
Start from maintenanceEnter a TDEE estimate or trend-calibrated maintenance value.
2,500 kcal/dayAdd a chosen surplusKeep the daily and weekly energy amounts visible.
+250 kcal/dayTreat time as linear contextUse 7,700 kcal/kg only as a check, then calibrate from trend.
Not a muscle-gain forecast.Interpretation
kcal/day is maintenance plus the entered surplus.
The timeline is a linear energy equivalent, not a guaranteed date.
No muscle-versus-fat split is predicted.
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Related calculators and resources
Method and test recordFormula v1.0.0
- Recorded scope
- health-nutrition-foundations
- Publisher
- CalculatorGeek
- Recorded review date
- 2026-10-04
- Next source review
- 2027-10-04
- Definition fixtures
- 4 configured scenarios
- Published examples
- 4 shown below
Recorded method
Verify calorie addition, weekly energy, metric-imperial target parity, 7,700-kcal/kg arithmetic, target-direction constraint, and invalid inputs.
These records describe the published model and reference tests. A test-case count is not a certification of every possible input or an independent specialist review. Editorial policy
Known limitations
- Actual weight gain changes maintenance needs and is not linear.
- The energy density of gained tissue is not fixed.
- The tool cannot predict muscle-versus-fat gain.
- Health conditions, underweight, appetite problems, eating disorders, pregnancy, and medications require professional assessment.
Method sources
- NIDDK: Body Weight Planner
- NIDDK: Dynamic body-weight model and limitations of linear rules
- National Academies: Dietary Reference Intakes for macronutrients
Latest model update
2026-10-04 - Initial CalculatorGeek shared-system nutrition implementation with source-backed method, fixtures, content, and result journey.
Reference inputs and expected results
Up to 12 examples from the configured definition fixtures are shown. Expected values use the stated output units; invalid inputs are intended to be rejected.
| Case | Inputs | Expected result |
|---|---|---|
| five kilogram reference | Estimated maintenance calories: 2500 kcal; Selected daily calorie surplus: 250 kcal; Current weight: 70 kg; Exploratory target weight: 75 kg | Daily calorie planning target: 2750 kcal/day; Seven-day energy surplus: 1750 kcal/week; Linear weight-change equivalent: 0.2272727273 kg/week; Linear timeline equivalent: 22 weeks (allowed numeric tolerance: 0.0001) |
| imperial parity | Estimated maintenance calories: 2500 kcal; Selected daily calorie surplus: 250 kcal; Current weight: 154.323584 lb; Exploratory target weight: 165.346697 lb | Selected weight change: 5 kg; Linear timeline equivalent: 22 weeks (allowed numeric tolerance: 0.001) |
| minimum surplus boundary | Estimated maintenance calories: 2200 kcal; Selected daily calorie surplus: 25 kcal; Current weight: 60 kg; Exploratory target weight: 61 kg | Daily calorie planning target: 2225 kcal/day; Seven-day energy surplus: 175 kcal/week |
| invalid target direction | Estimated maintenance calories: 2500 kcal; Selected daily calorie surplus: 250 kcal; Current weight: 70 kg; Exploratory target weight: 70 kg | Reject invalid input: target_weight |
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On this page
What the Weight Gain Calculator answers
Add a user-selected calorie surplus to maintenance and inspect the linear energy-equivalent timeline without presenting it as a guaranteed weight forecast.
The calculator keeps maintenance, surplus, weekly energy, target change, and the 7,700-kcal/kg assumption visible.
Start with the Health calculators hub when you need a different nutrition or body-measurement workflow.
How to use the Weight Gain Calculator
- Enter an estimated or calibrated maintenance intake.
- Enter the daily surplus you want to model.
- Enter current and exploratory target weight.
- Use the timeline only as linear context and revise from a consistent measured trend.
For the closest upstream or downstream calculation, use the TDEE Calculator. Estimate maintenance before adding a surplus.
Formula, variables and calculation order
target calories = maintenance + daily surplus.
linear weekly equivalent = daily surplus × 7 / 7,700 kg/week and linear weeks = selected weight change / weekly equivalent. NIDDK’s dynamic model explains why fixed energy-per-weight rules do not predict long-term change precisely.
To compare this result with a related method, open the Lean Bulk Calculator. Allocate a selected surplus into macro planning outputs.
Worked examples and boundary checks
2,500 maintenance plus 250 kcal/day
The target is 2,750 kcal/day and weekly surplus is 1,750 kcal. The linear equivalent is about 0.23 kg/week; 5 kg corresponds to about 22 weeks in this simplified arithmetic.
Boundary check
The tool rejects a target at or below current weight because that is a different user task, and it never labels the 22-week value a promised completion date.
How to interpret the result
The primary target is directly auditable. The body-weight outputs are secondary energy-equivalent context whose largest assumptions are displayed.
- Actual weight gain changes maintenance needs and is not linear.
- The energy density of gained tissue is not fixed.
- The tool cannot predict muscle-versus-fat gain.
- Health conditions, underweight, appetite problems, eating disorders, pregnancy, and medications require professional assessment.
For another relevant cross-check, continue with the Macro Calculator. Split a chosen calorie target into grams.
Inputs, outputs and result meaning
Keeps energy arithmetic auditable, validates gain direction, separates primary calorie target from secondary linear timeline, and refuses to predict muscle-versus-fat gain.
Inputs
- Estimated maintenance calories
- Use a separate TDEE estimate or a maintenance value calibrated from a trend.
- Selected daily calorie surplus
- This is a user-selected planning input, not an automatically recommended amount.
- Current weight
- Use a current measured weight.
- Exploratory target weight
- Must be greater than current weight for this gain workflow.
Outputs
- Daily calorie planning target
- Reported in kcal/day as the primary result.
- Seven-day energy surplus
- Reported in kcal/week.
- Linear weight-change equivalent
- Reported in kg/week.
- Selected weight change
- Reported in kg.
- Linear timeline equivalent
- Reported in weeks.
Keep the result, selected inputs, unit labels, and stated limitations together when saving or sharing the calculation.
Frequently asked questions
Will I gain exactly the displayed amount each week?
No. Energy expenditure, tissue composition, water, glycogen, appetite, and adherence change over time.
How much will be muscle?
This calculator does not predict muscle-versus-fat gain. Training status and program quality cannot be converted into a reliable split here.
Where should maintenance come from?
Use a transparent TDEE estimate or calibrate maintenance from several consistent weeks of intake and weight data.
Why use 7,700 kcal/kg?
It provides recognizable linear energy arithmetic, while the page explicitly warns that dynamic body-weight change is more complex.
Who should seek professional guidance?
People with unexplained weight loss, underweight, eating-disorder history, pregnancy, or a medical condition should use qualified care.
Primary sources and evidence limits
- NIDDK: Body Weight Planner
- NIDDK: Dynamic body-weight model and limitations of linear rules
- National Academies: Dietary Reference Intakes for macronutrients
Sources were checked 2026-10-04. They support the named equation, reference range, label arithmetic, or evidence boundary; they do not convert an estimate into individualized medical nutrition advice.