Sourdough Starter Planner
Build a levain to an exact weight and hydration: how much seed to keep, how much flour and water to add, and the starter left in the jar.
The levain is made of a seed starter plus added flour and water. A starter at 100% hydration is half flour and half water by weight, so a wetter seed brings some of the levain's water with it: the water to add is whatever brings the combined flour and water to the target hydration, and the feed ratio shown is seed : added flour : added water. With a seed at the same hydration as the target, the water to add is simply the target hydration percentage of the added flour, so a 1:5 feed at 100% reads 1 : 5 : 5. Fermentation mass loss and evaporation are not modelled, and none of this is food-safety guidance; weigh on a scale and use your normal starter routine.