The sourdough starter calculator for precise feeding and scheduling

How feeding ratios actually control your starter’s rise

A feeding ratio is really a dilution number dressed up as a recipe. In 1:1:1, every gram of starter meets one gram of fresh flour and one gram of water, so the yeast and lactic acid bacteria have a small amount of new food relative to their numbers and get through it fast, typically peaking in 3 to 5 hours. Push the ratio to 1:5:5 or 1:10:10 and you’re diluting that same population of microbes into a much bigger pool of fresh flour and water. There’s more for them to eat, so it takes longer to consume it all and build up enough gas to peak, which is exactly why higher ratios stretch out your timeline for an overnight build.

This calculator works backwards from what your recipe needs, not forwards from what’s sitting in your jar. It takes your target amount, adds a 20% buffer so you’ve got starter left over for the next feed, then splits that total across your chosen ratio to tell you exactly how much starter to pull, and how much flour and water to add. If your jar doesn’t hold enough mature starter to hit that full target, it scales the feed down to match what you’ve actually got, so the ratio stays correct even when the quantity is smaller. One thing worth doing every time: discard down to the exact starter figure the calculator gives you before you add anything. Feeding on top of leftover discard throws the ratio off, and it’s the single most common reason a starter that “used to be reliable” suddenly starts peaking early or late.

Building a sourdough starter from scratch

A new starter needs nothing more than flour, water and time, but the process trips people up because the early days look inactive even when the culture is developing normally underneath the surface. Mix equal weights of flour and water, roughly 50g of each to start, in a clean jar and leave it loosely covered at room temperature. For the first two or three days you may see little to no rise, sometimes even a slightly unpleasant smell, which is completely normal as an initial burst of less desirable bacteria briefly gets going before the wild yeast and lactic acid bacteria that define a healthy starter take over.

From around day three or four, begin discarding roughly half the starter and feeding with fresh flour and water once a day, using something close to a 1:1:1 ratio to keep the daily rhythm predictable while the culture establishes itself. By around day seven to ten, a starter fed on strong bread flour in a reasonably warm kitchen (21 to 24°C) usually starts doubling reliably within 4 to 8 hours of a feed, smells pleasantly sour rather than sharp or unpleasant, and is ready to use in a loaf. Cooler kitchens, or plain flour instead of strong bread flour, can push this out to two weeks or more. Patience matters more than any particular trick here: a starter that seems slow in week one is far more often just early in its development than actually failing.

Once established, this calculator becomes useful immediately, since it takes the guesswork out of scaling a young, still-small starter up to whatever quantity a recipe calls for, while keeping the ratio consistent with what got it active in the first place.

A realistic starter maintenance schedule

How often you feed a starter should match how often you actually bake, not the other way round. Bakers who make bread most days are usually best served keeping their starter at room temperature and feeding once or, for a very active culture, twice every 24 hours at a consistent ratio. This keeps the culture at peak strength and ready to use with minimal advance planning, but it does mean daily discard, which either gets used in discard recipes or composted.

For anyone baking less than a couple of times a week, room-temperature daily feeding is wasteful and unnecessary. Storing the starter in the fridge and feeding it once a week instead slows the culture right down without killing it, and it's the schedule most home bakers settle into long term. The trade-off is a day of advance planning: pull the starter out the evening before or the morning of the day before you want to bake, discard and feed as normal, and let it come back up to full strength at room temperature before using it in a recipe, exactly as covered above for reactivating cold starter.

Common starter feeding mistakes

Feeding ratio comparison: 1:1:1 vs 1:5:5 vs 1:10:10

The feeding ratio you choose is the single biggest lever on how your starter behaves, more than flour type, more than water temperature, more than almost anything else short of actual neglect. Each ratio trades off speed against mildness and yield, so the "best" one depends entirely on your schedule and how sour you like your bread. The table below lines up the three most common ratios side by side.

Times assume a healthy, active starter at 21°C room temperature. A warmer kitchen (26°C+) can roughly halve these times; a cold larder can double them.

Starter hydration by flour type

Most starter recipes default to 100% hydration, equal parts flour and water by weight, because it is easy to maintain and easy to measure into a recipe. But the flour you feed it with changes how that same 100% actually looks and behaves in the jar, since different flours absorb water differently.

Rye starters in particular ferment noticeably faster than white flour starters at the same ratio, thanks to rye's higher enzyme activity, so keep an eye on timing rather than relying purely on the clock.

What to do with sourdough discard

Every feeding schedule produces discard, the portion of starter removed before feeding to keep the culture at a manageable size. It's not waste. Discard still carries flavour and some residual activity, it just doesn't have the fresh food reserves to reliably lift a loaf on its own, so it's best used in recipes that don't depend on rise the way bread does.

The sourdough discard calculator on this page works out exact flour and water quantities for pancake and cracker recipes based on how much discard you have.

Troubleshooting by symptom

Most starter problems trace back to one of a handful of causes: temperature, feeding frequency, flour, or time since the last feed. Use the table below to go from what you're seeing in the jar to the most likely cause and fix, before you assume the culture itself is dead, which is rarer than it looks.

If you're seeing genuine mould, fuzzy patches, or anything beyond harmless hooch and streaks of surface liquid, the safest move is always to discard the starter and begin a new one rather than trying to rescue it.

A quick note from Benjie: my own starter has been going for a few years now, fed on a fairly relaxed 1:5:5 most weeks unless I've got a big bake planned. Treat it a bit like debugging code, if it's stopped doubling the way it used to, check your inputs first (flour, temperature, timing) before assuming the culture itself is broken. It almost never is.