How it works: Total = starter for your recipe + extra. Each ingredient = total × its part ÷ all parts, so at 1:5:5 the starter is 1/11 of the total. Hydration after feeding counts the flour and water already in your starter (starter flour = starter ÷ (1 + hydration)). Peak time grows with the ratio and roughly doubles for every 7 °C (12 °F) cooler; treat it as a planning guide.

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What the feeding calculator is for

A sourdough starter is a small colony of wild yeast and lactic acid bacteria living on flour and water. Every feed dilutes the old culture with fresh food, and the ratio you pick decides two things: how much starter you end up with, and how long it takes to reach its peak. This tool works out the first part exactly and gives you a planning estimate for the second.

It is built for home bakers who have looked at a recipe asking for 150 g of active starter and wondered how much to take out of the jar. You tell it what you need, choose a ratio, and it returns the three weights to stir together.

Filling in the fields

In Starter for your recipe, enter the weight of starter or levain your recipe calls for.
In Extra to keep in the jar, add what you want left over to keep the culture going. Somewhere between 20 and 30 g is plenty for most home kitchens.
Pick a ratio from Starter : flour : water. The first number is the ripe starter you carry over, the other two are fresh flour and water. Choose Custom ratio if you want to type your own Starter parts, Flour parts and Water parts.
Set Current starter hydration. Most starters live at 100%, which simply means equal weights of flour and water.
Enter your Room temperature so the timing estimate reflects your kitchen.
Read the three amounts under Mix this, then check Hydration after feeding and Time to peak (guide).

Worked example: 150 g for tomorrow’s loaf

Your loaf needs 150 g of starter and you like to hold back 25 g for the next feed. The kitchen sits at 22 °C and you feed at 1:2:2. The calculator returns:

Starter: 35 g
Flour: 70 g
Water: 70 g
Total after feeding: 175 g
Hydration after feeding: 100%
Time to peak (guide): about 6 h 30 min to 9 h 45 min

A 1:2:2 feed has five parts, so each part is 175 ÷ 5 = 35 g. The ripe starter gets one part, while flour and water get two each.

Now switch the same bake to an overnight 1:5:5 feed in a cooler 20 °C room. The starter drops to 16 g, flour and water rise to 80 g each, and the estimate stretches to about 11 h to 16 h 30 min. With far fewer microbes at the start, they need longer to work through all that fresh flour, and the cooler room slows them further. Because each amount is rounded to the nearest gram, the three weights can add up to a gram more or less than the total.

Treat that range as a planning guide rather than a promise. It assumes a lively, well-fed starter at the stated room temperature, and flour type, the age of your culture or a draughty windowsill can move the real peak by a couple of hours.

Tips and common mistakes

Watch the starter, not the clock. A ripe starter has roughly doubled, has a domed or just-flattening top and smells pleasantly sour.
Always add a little extra. Mix exactly what the recipe needs and some will stay stuck to the jar and spatula, leaving you short.
Whole wheat and rye speed things up. They carry more nutrients and wild microbes than white flour, so expect an earlier peak.
Tell the calculator about a stiff starter. If yours is kept at 60%, set Current starter hydration to 60 and a 1:2:2 feed comes out at 90% instead of 100%, because the carried-over portion brings less water.
Tiny feeds are hard to weigh. When the starter works out under 1 g, the calculator warns you. Feed a bigger batch and discard the surplus.

Building a separate levain for a specific recipe? The levain builder handles target hydration and flour blends. To see how this feed fits into a whole bake day, open the sourdough schedule planner.

Questions bakers ask about feeding

Which feeding ratio should I choose?

It depends on when you need the starter. A 1:1:1 feed in a warm kitchen peaks within a few hours and suits a same-day bake. Higher ratios such as 1:5:5 or 1:10:10 slow everything down, which helps with overnight feeds or a hot summer kitchen where a 1:1:1 feed would collapse while you sleep.

Is it a problem if my starter is past its peak when I feed it?

A little past peak is fine, and the next feed usually brings it back. If it has sat for days and smells sharp or of nail polish remover, give it two or three feeds, 12 hours apart, before trusting it in a loaf.

Why does the calculator care about the water already in my starter?

The portion you carry over becomes part of the new mixture. With a 100% starter it makes no difference, but a very stiff or very runny culture shifts the final hydration, and that changes how quickly it rises and how it behaves in dough.

How much starter should I keep between bakes?

Keeping 20 to 50 g is enough for most home bakers. A smaller jar means less discard, and you can always build up the amount with a larger ratio the day before you bake.