Weight Gain Calculator

Written by Great Medico

Updated September 24, 2026 •2 min read

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A useful nutrition estimate should be simple enough to apply and specific enough to understand. Weight Gain Calculator focuses on one calculation at a time.

What this calculator does

Planning weight gain is easier when a target weight, pace, and estimated maintenance intake are connected. This calculator adds a fixed calorie surplus for the selected pace and estimates how long the entered weight difference could take under a simple energy model. Nutrition equations are planning tools: real energy and nutrient needs still vary with physiology, goals, health conditions, and the quality of the input data.

How to use it

Enter or select Sex, Height, Weight, Age, Activity level, Target weight, and Weight gain pace. Use the units offered by the calculator and keep measurements consistent when you plan to compare results over time.

How the calculation works

Maintenance calories are estimated with Mifflin–St Jeor BMR × activity factor. The engine adds about 250 kcal/day for slow, 500 for moderate, or 750 for fast gain. Estimated time uses the weight difference × 7,700 kcal/kg divided by the selected daily surplus.

Example

For the sample values prefilled in this calculator, the primary result is 3018 kcal/day (Weight-gain calorie target), Estimated maintenance is 2,518 kcal/day, and Daily surplus is 500 kcal/day. This example is there to show how the inputs flow through the implemented equation; replace the sample values with your own measurements before using the result.

How to interpret the result

The output gives a calorie target and approximate time to reach the entered target if the simplified assumptions held. In practice, body weight and energy expenditure change during a gain phase.

Limitations and notes

The 7,700-kcal-per-kilogram relationship is a rough planning rule and does not predict the split between muscle and fat. Very fast gain may increase fat gain, while illness, pregnancy, sport goals, or underweight treatment can require individualized targets.