Sourdough Starter Feeding Calculator

The Sourdough Starter Feeding Calculator turns a feeding ratio into exact flour and water weights and then answers the question every other feeding calculator leaves out: when will the jar actually peak? Feeding is only half the job — a starter is at its strongest for a couple of hours around its peak, and hitting that window is what separates a levain that lifts a loaf from one that merely tastes sour.

What a Feeding Ratio Really Means

A feeding ratio is written seed : flour : water and is always measured by weight, never by volume. In a 1:5:5 feed you keep one part of your existing starter and add five parts fresh flour and five parts water. The ratio says nothing about how much starter you end up with — that depends on the seed — and everything about how diluted the culture is, which is what sets the clock.

So 20 g of seed on a 1:5:5 feed takes 100 g of flour and 100 g of water and gives 220 g of refreshed starter. Keep 20 g again next time and the maths repeats forever, which is why bakers talk in ratios rather than grams.

Why the Ratio Controls the Clock

Every feed dilutes the yeast and bacteria into a much larger volume of fresh flour. The culture then has to multiply back up before the jar visibly rises. Halving the amount of colonised flour means roughly one extra doubling, so the wait grows with the logarithm of the ratio, not in proportion to it. That is why a 1:10:10 feed takes about ten hours rather than ten times as long as a 1:1:1.

The calculator uses inoculation rather than the raw ratio because it also accounts for the hydration of your seed. A 50% stiff starter carries two-thirds of its weight as flour, so the same 1:5:5 feed inoculates a stiff jar more heavily than a liquid one — and it peaks sooner.

Feeding Ratio and Peak Time Chart

Approximate times for a 100% hydration white-flour starter. Warmer or cooler kitchens shift every row: each 8 °C (about 14 °F) of extra warmth roughly halves the wait.

Reading the Jar Instead of the Clock

The predicted time is a very good starting point, but the jar is the real authority. A ripe starter is domed rather than flat, webbed with bubbles at the glass, smells yeasty and faintly sweet-sour, and lifts a spoonful that floats. Once it flattens, wets on top and starts to smell like acetone or nail polish, it has gone past peak and needs feeding rather than baking.

Choosing a Ratio for Your Schedule

Pick the ratio that makes the starter peak when you are actually free. A 1:1:1 or 1:2:2 feed suits a same-day bake where you want a levain in a few hours. A 1:5:5 is the everyday maintenance feed and lands in a half-day rhythm. A 1:10:10 or wider gets you through the night so the jar is ready at breakfast, and it also produces a milder, less acidic starter because the culture spends less of its life in an exhausted, sour state.

How to Use This Calculator

1. Enter your starter amount: Type how much starter you will keep as the seed, or switch the mode to work backwards from the ripe levain weight your recipe needs.
2. Choose a feeding ratio: Tap a ratio chip such as 1:5:5, or type your own flour and water parts, and set the hydration you keep the starter at.
3. Describe your kitchen: Enter the room temperature in °C or °F and pick the flour you feed with — rye and whole wheat are noticeably faster.
4. Add a feeding time (optional): Enter the clock time of the feed and every stage of the timeline comes back as a real time of day.
5. Click Calculate Feeding: Read the flour and water weights, the rise curve, the ripe window, the discard amount and the schedule table for your temperature.

Frequently Asked Questions

What is a sourdough starter feeding ratio?

A feeding ratio is written seed : flour : water and is always measured by weight. In a 1:5:5 feed you keep one part of your existing starter and add five parts fresh flour and five parts water, so 20 g of seed takes 100 g of flour and 100 g of water. The ratio does not change what the starter is, only how much food it gets, which is what controls how long it takes to peak.

How much flour and water should I feed my starter?

Multiply the weight of the starter you are keeping by each part of your ratio. For a 1:2:2 feed with 25 g of seed that is 50 g of flour and 50 g of water, giving 125 g of refreshed starter. Feeding equal weights of flour and water keeps a 100 percent hydration starter at 100 percent; feeding less water than flour makes it stiffer and slower.

How long does a sourdough starter take to peak after feeding?

At around 24 degrees Celsius a 1:1:1 feed usually peaks in about 4 hours, a 1:5:5 in about 8 hours and a 1:10:10 in about 10 hours. Temperature matters as much as the ratio: every 8 degrees Celsius cooler roughly doubles the wait, so the same 1:5:5 jar that peaks in 8 hours at 24 degrees needs closer to 13 hours at 18 degrees.

What does a 1:5:5 feeding ratio mean?

It means one part starter to five parts flour to five parts water by weight. It is the most common maintenance feed because it lands in a convenient half-day rhythm at room temperature, produces a mild rather than sharply sour culture, and leaves enough headroom in the jar for a rise of roughly three times the post-feed level.

Do I have to discard starter every time I feed it?

You have to remove starter, but you do not have to throw it away. Discarding keeps the jar from growing without limit and keeps the inoculation low enough that the fresh flour actually feeds a young culture rather than an exhausted acidic one. Keep the removed portion in a separate jar in the fridge and use it in pancakes, waffles or crackers.

How do I time a feeding so the starter is ready when I want to bake?

Work backwards from the bake. Enter the hours until you need it and the calculator picks the ratio that peaks at that moment, because a bigger feed simply takes longer to climb. A larger ratio buys you time, a warmer spot buys you speed, and if the numbers still do not line up you can feed as normal and refrigerate the jar once it is ripe.

Additional Resources

• Sourdough - Wikipedia
• Pre-ferment - Wikipedia
• Baker Percentage - Wikipedia