How this calculator works
A sourdough starter is a mixture of flour and water that is already partly fermented. When you add starter to a dough, some of the total flour and water arrives with it. This calculator accounts for that split: it first finds the total flour from your target dough weight and baker's percentages, then takes the starter as a share of that flour, divides the starter into its flour and water, and calculates only the extra water needed to reach the chosen hydration. The result is that total water, including the starter water, is exactly the hydration percentage of the total flour.
Formula
total flour = target dough weight / (1 + hydration + salt). starter = total flour x starter share. starter flour = starter / (1 + starter hydration). starter water = starter - starter flour. added water = total flour x hydration - starter water. salt = total flour x salt share. total dough = total flour + total water + salt.
Worked example
A 1,000 g country loaf at 75 per cent hydration, 20 per cent starter, 100 per cent starter hydration and 2 per cent salt. The total flour is 1,000 / (1 + 0.75 + 0.02) = 564.97 g. The starter is 113 g, of which 56.5 g is flour and 56.5 g is water. Total water is 423.7 g, so add 423.7 - 56.5 = 367.2 g. The salt is 11.3 g. The pre-fermented flour is 56.5 / 565 = 10 per cent of the total.
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Frequently asked questions
What does hydration actually mean?
It is the weight of water divided by the weight of flour, expressed as a percentage. A 75 per cent hydration dough has 75 g of water for every 100 g of flour. It does not include the flour and water that arrive inside the starter, which is why the calculator separates them out.
How much starter should I use?
A common range is 15 to 25 per cent of the total flour for a same-day bake. More starter ferments faster and shortens the bulk rise; less starter slows everything down and suits a colder, longer process. Starter hydration also changes the amount of water it brings with it.
Why does the calculator say the starter has more water than allowed?
A very wet starter at a low dough hydration can use up the water budget before any extra water is added. For example, 50 per cent starter at 150 per cent starter hydration contains more water than a 60 per cent dough allows. Lower the starter share, raise the dough hydration, or use a stiffer starter.
How much salt should sourdough have?
Most bakers use 1.8 to 2.2 per cent of the flour weight. Salt strengthens the gluten and slows fermentation. Going much below 1.5 per cent gives a slack, fast dough; much above 2.5 per cent can taste harsh and slow the yeast too much.