How to use this calculator
Weigh the flour you plan to add, then choose a target hydration. Enter the weight of ripe starter and its hydration separately. The result deducts the water already in that starter and bases the salt on all the flour in the dough. Use grams throughout; cups introduce a different uncertainty.
The starter makes the difference
For the example above, 100 g of starter at 100% hydration contains 50 g flour and 50 g water. Adding it to 500 g flour gives 550 g total flour. At 70% hydration you need 385 g total water, so pour in 335 g more. Salt at 2% is 11 g. The ingredients sum to 946 g of dough.
The calculation
Starter flour = starter weight ÷ (1 + starter hydration ÷ 100). Starter water is the rest of its weight. Water to add = total flour × target hydration ÷ 100 − starter water. If that last number is negative, the recipe cannot reach the requested hydration without changing the inputs.
Before you mix
This tool assumes the starter contains only flour and water. Milk, eggs, syrups, soaked grains and other wet ingredients require separate accounting. Hydration describes a ratio; flour type, mixing, temperature and fermentation also affect handling. A calculated quantity does not predict when bread is ready to bake.
Questions, answered
Does this include the starter in hydration?
Yes. Both its flour and water count. A stiff starter and a liquid starter can contribute different amounts even when they weigh the same.
Can I use this without starter?
Enter zero for starter weight. Water is then simply added flour multiplied by the hydration percentage.
Why is my water lower than 70% of the flour I entered?
The starter contributes both extra flour and existing water. The calculator solves for the water still needed, rather than treating the starter as a separate ingredient outside the ratio.
Further reading: King Arthur Baking: baker’s percentage. The examples and tools on this page use the assumptions stated above.