A sourdough formula with 500 g total flour includes flour inside the starter. It does not mean 500 g fresh flour followed by a starter addition whose flour is ignored.
The Whatson Sourdough Recipe Calculator starts from total flour, target hydration and the percentage of flour that is prefermented. It then shows what is already in the prepared starter and what remains for the final mix.
Twenty percent refers to flour, not starter mass
For a total flour target of 500 g and a 20% prefermented flour share, 100 g flour belongs in the starter. At 100% starter hydration, it is accompanied by 100 g water, giving 200 g prepared starter.
The starter mass is therefore 40% of the total flour mass in this example. Entering 20% as though it described total starter mass would produce a different allocation.
The checked 70% hydration formula
Enter 500 g total flour, 70% target hydration, 20% prefermented flour, 100% starter hydration and 2% salt.
| Ingredient | Already in starter | Add in final mix |
|---|---|---|
| Flour | 100 g | 400 g |
| Water | 100 g | 250 g |
| Salt | 0 g | 10 g |
The prepared starter is 200 g. Combined formula mass is 860 g: 500 g flour, 350 g water and 10 g salt. Do not add the 200 g starter again to that total.
A wetter starter can use more of the water budget
The water in the starter is subtracted from target total water. If the entered prefermented share and starter hydration put more water in the starter than the formula permits, the tool rejects that combination rather than reporting negative fresh water.
Change the share, starter hydration or target formula deliberately. The error is an accounting conflict, not a diagnosis of starter quality.
Feeding and fermentation remain separate tasks
Use Sourdough Starter Feeding Calculator to calculate a feed for your own seed starter. This recipe allocation assumes the required prepared starter is available; it does not generate a feeding timetable or include a reserved maintenance amount.
Dough Hydration Calculator can check total hydration when you already know the fresh flour, water and starter quantities. It solves the percentage from amounts, whereas this tool solves amounts from a target percentage.
Record the starter hydration and flour share in the recipe note, along with your method. The schedule is an ingredient calculation, not a promise of proofing time, rise, flavour or kitchen tested results.