For physical stats, our calculator asks for age, height, weight, gender, and body fat %. Why is this?
If you enter a body fat %, it will use a formula known to be more accurate than the alternative. If you don’t enter one, it will estimate using an alternative formula, based on the other factors. These estimates make assumptions about typical outputs for different age groups, genders, etc.
The output of these formulas is your Resting Metabolic Rate (RMR). In other words, what your body needs just to exist, without any activity on top. Let me be clear – your activity does not impact this number at all. We’re talking about what you need to breathe, have a heartbeat, etc.
What impacts it is lean muscle mass – the percentage of muscle you have on your body, relative to your overall weight.
The more lean mass you have, the more efficient you are at burning calories simply by existing.
Try it! Pull up the calculator and and input all the fields, including BF%. Now go back and change the age, height, or sex and observe that the Maintenance Calories DO NOT CHANGE.
Note that a super accurate body fat % can also be hard to pin down. You can get a Dexa Scan, an Inbody, or estimate based on measurements or photos. It’s ok if this number isn’t perfect – just keep in mind for later that this number can impact your results.