Sourced calculator and guide
Weight gain calculator: starting calorie scenarios
Calculate a starting calorie scenario by adding your chosen surplus to estimated maintenance. You supply the surplus; the tool does not prescribe it.
Calculate your estimate
Enable JavaScript to edit inputs. The worked examples below remain available without it.
Confirm the adult scope before calculating. This tool excludes pregnancy and breastfeeding.
Worked examples from the same calculator
Unless the row says otherwise: age 30, 70 kg, 175 cm, male coefficient. PAL 1.4–1.6 is an illustrative, explicitly chosen scenario. Surplus is 250 kcal/day unless specified; these amounts are examples, not prescribed targets. Only the final output is rounded using decimal half-up rules.
| Input scenario | Estimate |
|---|---|
| Illustrative surplus 250 | 2558 to 2888 kcal/day |
| Illustrative surplus 100 | 2408 to 2738 kcal/day |
| No added surplus | 2308 to 2638 kcal/day |
Starting calories for a weight-gain scenario
Starting intake estimate = estimated maintenance + user-chosen surplus. Maintenance uses unrounded Mifflin REE multiplied by your chosen PAL endpoints. The tool has no default surplus; the 250-kcal example is arithmetic for illustration, not a recommendation.
What the calorie scenario does not establish
A chosen surplus does not guarantee a particular amount or composition of weight gain. It is not a plan for a clinical condition. Actual expenditure and intake vary, and both may change over time.
No static target-weight timeline
Hall’s dynamic energy-balance work shows why static calorie-to-weight conversions cannot establish a reliable timeline. This tool does not implement that model and makes no target-weight or target-date prediction. Use the maintenance guide for energy-balance context.
Source formulas and scope
The simplified equations in the original Mifflin–St Jeor PubMed abstract read:
REE (males) = 10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) + 5; REE (females) = 10 x weight (kg) + 6.25 x height (cm) - 5 x age (y) - 161.
Output is estimated REE in kcal/day. Original study: 498 healthy adults, ages 19–78. This tool excludes children, pregnancy and breastfeeding; it provides no medical advice. The equation’s two coefficients reflect the study, and do not establish validation for other populations. US inputs use exactly 1 lb = 0.45359237 kg and 1 in = 2.54 cm without intermediate rounding. Other maximum input limits only prevent extreme or accidental entries; they are not clinical thresholds.
NIDDK’s PAL guidance states:
Typical physical activity level numbers range from 1.4 (sedentary) to 2.5 (very active).
REE × PAL is this tool’s initial approximation of total daily expenditure. PAL is selected by you, separately from the original resting-energy equation. Ranges reflect the entered scenarios, not personal error bounds. Hall et al. describe the static rule as “This ubiquitous weight-loss rule (also known as the 3500 kcal per pound rule)” and explain that it ignores physiological adaptations. The dynamic Hall model is not implemented here; no weight-change timeline is calculated.
Questions and answers
What does this weight gain calculator calculate?
It adds a surplus you enter to an estimated maintenance range. It produces starting calorie scenarios only, without predicting pounds gained or a date.
Is the surplus a recommended amount?
No. You choose it. The worked examples demonstrate arithmetic and are not a medical or dietary prescription.
Sources
Reviewed October 29, 2026. Original formulas are quoted above; derived scenario arithmetic is identified separately.