what hydration is this starter?

yes - the only difference is that it weighs 80 grams more and some might call it a levain.

There is a tutorial for that. And lots of good information is available in other forum topics. Use the search bar at the top right of the page to find out all about Bakers' Math!

The easiest way to calculate this, since we have the 20g starter at 100% hydration, is to divide the starter, add the flour and water from the starter to the other flour and water, then re-divide to find final hydration.

So 20g / 2 = 10g each of flour and water

40g flour + 10g flour = 50g flour

40g water + 10g water = 50g water (you should see now where this is heading)

50g water / 50g flour = 100% hydration

Let's see how different numbers would give us a different outcome. Let's say that you have 20g starter at 100% hydration, but you are mixing it with 50g flour and 35g water. Well, the calculation would work the same way.

20g / 2 = 10g each flour and water

10g flour + 50g flour = 60g flour

10g water + 35g water = 45g water

45g water / 60g flour = 75% hydration