How this calculation works
Baker’s percentages use total flour as the common base. Split the preferment into its flour and water before calculating what remains to add. Its flour counts toward both the total dough and the selected flour blend exactly once.
Total flour = target dough / (1 + hydration + salt + extras); fresh water = overall water − preferment waterA worked example
For 1,000 g dough at 70% hydration and 2% salt, total flour is about 581.40 g. If 20% of that flour is prefermented at 100% hydration, the preferment carries about 116.28 g flour and 116.28 g water; add about 290.70 g fresh water.
Good to know
Preferment includes only flour and water, with the same flour blend as the overall dough. Extra ingredients are not automatically decomposed into their own water/flour. No fermentation, dough-loss or food-safety prediction.
Reference: King Arthur Baking: overall baker’s percentages (opens in a new tab) ↗
Make total flour the common denominator
In baker’s percentages, total flour is 100%. Water, salt and other ingredients are measured relative to that flour, so the percentages normally add to more than 100. This differs from expressing every ingredient as a share of the final dough.
Dividing the target mass by the sum of the flour-based factors gives the flour needed. The remaining overall masses follow from it. This is a mass balance; it does not prescribe a suitable hydration or salt amount for a particular bread.
Split the preferment into flour and water
Prefermented flour is a share of all flour in the final dough. The preferment hydration uses its own flour as the base. At 100% hydration, it carries equal flour and water masses.
Subtract those carried quantities before calculating fresh additions. Adding the preferment on top of a complete flour/water recipe would count them twice. If its water already exceeds the overall water budget, the inputs are inconsistent and must be changed.
Keep blend and extra-ingredient assumptions explicit
The selected wholemeal share is applied to both fresh and prefermented flour. A starter with a different flour blend requires a more detailed ingredient ledger than this model. The table exposes the assumed contributions rather than hiding them in one starter mass.
Other ingredients are represented as a combined flour-based percentage. Their own water, flour or salt is not automatically extracted. Butter, milk, eggs and enriched preferments can therefore need a more detailed formulation before this simplified balance is suitable.
Separate formula scaling from fermentation
The cake pan recipe scaling calculator compares geometric batter capacities. This tool instead solves ingredient masses from an overall dough formula and a defined preferment contribution, so the two pages answer different tasks.
Time, temperature, fermentation strength, mixing, loss during handling and food safety remain outside the calculation. Check the table’s total against the desired dough mass, then use a tested recipe and process rather than interpreting a correct mass balance as a baking guarantee.
A few questions, answered
Does 20% preferment mean 20% starter mass?
No. The input is the proportion of total flour that is prefermented.
Why is fresh water lower than total water?
Some water is already inside the preferment.
Can the starter use a different flour blend?
This model assumes the same blend in fresh and prefermented flour; a different starter needs a fuller ledger.