Sourdough Levain Calculator

A levain is the portion of your final dough's flour and water that gets pre-fermented with a small amount of mature starter before mixing the main dough. This calculator works backward from your total recipe flour: it multiplies total flour by your prefermented-flour percentage to get the flour that belongs in the levain, then multiplies that flour by your starter's hydration percentage to get the water portion — so a 100%-hydration starter contributes equal parts flour and water, while a stiffer 60%-hydration starter contributes proportionally less water. Adding those two gives the total levain weight, and the seed starter amount is simply that total levain weight multiplied by your seed percentage — the fraction of mature starter used to inoculate the fresh flour-water mixture at the start of the build.

Build time is a simple heuristic, not a fermentation model: it starts from a baseline of 8 hours at 20% seed and 100% hydration, then scales inversely with seed percentage (more seed inoculant means faster ripening) and applies a flat 20% time penalty for stiffer-than-100% hydration starters, since less water slows microbial activity. This estimate doesn't account for ambient temperature, starter vigor, or flour type, all of which meaningfully shift ripening time in practice — use it as a rough planning number and confirm your levain is ready by sight (domed, bubbly, just past its peak) rather than by the clock alone. A common mixup: prefermented flour percentage refers only to the fraction of your recipe's total flour going into the levain, not the levain's own hydration.