## Deriving Stats from other Stats

Stats can be calculated from mathematical expressions that combine several other stats. In a previous example on the Mathematical Expressions article, we demonstrated how a stat called `StrMod` could be calculated using the current value of an existing Stat called `Str`.

This can be expanded to include expressions completely comprised of other stats.

Let's take a theoretical set of system rules where `Strength` and `Agility` are two Stats on a character. The combined value of those Stats makes up another Stat, called `Fitness`. Now we'll have another Stat called `MaxHP`, which is your `Fitness` score, multiplied by `5`.

Let's make the value of `Strength` to be `2` and the value of `Agility` to be `3`. These are each basic Stats.

Our first derived Stat will be `Fitness`. We'll write the value of `Fitness` to be `{Strength + Agility}`. Notice that when you make this change, the value of `Fitness` will become `5`. Our next derived Stat will be the Max HP score. So, for the Stat `MaxHP`, we will provide the value `{Fitness * 5}`. 