Sourdough Levain Calculator

About this calculator

A sourdough levain is a small portion of the final dough's flour, fermented separately with water and a spoonful of mature starter before it's mixed into the main dough. Bakers plan it using baker's percentages: a common build uses roughly 15–25% of the recipe's total flour as the levain's flour, at 100% hydration (equal weights of flour and water), inoculated with a starter "seed" typically 10–20% of the levain's flour weight.

Sizing this correctly matters for timing as much as flavor — a levain built too small or too cold ferments slowly and may underperform the main dough's rise, while an oversized or overly ripe levain turns a loaf sour and slack. Working backward from total flour and the target levain percentage tells a baker exactly how much flour, water and starter seed to combine, and when to start the build relative to the final mix.