The only thing that makes bakers math complicated is some do it one way and others another but essentially both make the same assumption. The assumption is that the main flour from the recipe is king and all other ingredients bow to it. Also you must remember that baker’s math is about weight. You can't work baker’s math with volume.
So how do you work it out?
1, To get the number of the king divide 100 by the main flour. Write this number down as all other ingredients must bow to it.
2, Multiply every ingredient in the recipe by the king's number. That's it. It really is that simple.
So why all the confusion?
It really comes down to what you decide is 'the main flour'. Do you include flour from the starter? Do you include other types of flour you are going to use, for example rye? To confuse things just a little more some will mix real percentages in, but don't worry about this, always make the assumption that it is pure baker's math and if the author is worth the salt in the recipe they will explain the differences.
The king's number is 100/596 = 0.1677
Starer Flour Water Salt Total20g 596g 394g 12g 1000g
3% 100% 66% 2% 168%