How this bulking calorie calculator works
The calculator first estimates resting energy expenditure with the Mifflin–St Jeor equation, published in the American Journal of Clinical Nutrition. It then applies the activity factor you select to create a rough maintenance estimate and adds your chosen daily surplus.
The result is an estimate—not a direct measurement of your metabolism. Activity categories are broad, food logs contain estimation error, and individual response varies.
What your result means
The useful test is whether your average intake and body-weight response move together in the direction you intended.
Resting needs
An equation-based estimate of the energy your body would use at rest. This is not your daily eating target.
Estimated maintenance
Resting needs multiplied by the selected activity level. Treat this as a rough baseline.
Starting surplus
The extra calories added above estimated maintenance. The NHS suggests that adults seeking gradual weight gain could try adding around 300–500 calories per day, while also emphasizing balanced food choices.
Why the target may need to change
A formula cannot see how your actual body weight responds. BulkBro starts with a target, then connects completed daily logs with your weekly weight response. When the observed result differs from the intended pace, the app can make a measured adjustment and record why.
That feedback loop is the key difference between calculating a number once and managing a real weight-gain plan.
Read the full guide to choosing and adjusting a weight-gain calorie target →
Choose a calorie surplus for muscle gain →
Choose a target rate of weight gain →
Troubleshoot why your weight may not be increasing →
Sources and methodology
- Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals.
- NHS: Healthy ways to gain weight.
- NIDDK: About the Body Weight Planner.