Yeast to Sourdough Conversion: The Math, the Timing, and What Most Blogs Skip

You've got a recipe you love. It calls for 7g of instant yeast, and you want to make it with your starter instead. The swap isn't a one-liner, but it's not black magic either. It's mostly a bit of math and a lot more patience. This guide walks through the whole thing: ratios, flour and water adjustments, timing, temperature, and a full worked example at the end.

The short answer (ratios you can actually use)

Here's the baseline most bakers use:

100g of mature, active 100% hydration starter ≈ 5–7g instant yeast ≈ 7–10g active dry yeast ≈ 20–30g fresh yeast

So if your recipe calls for 7g of instant yeast, you'd swap in roughly 100g of starter. That's the number you'll see repeated across every sourdough blog, and it's a decent starting point.

But notice it's a range, not a fixed number. That's not sloppy math; it reflects real variables. How active your starter is matters enormously. A starter that doubles in four hours on a warm day behaves very differently from one that takes eight hours in a cold kitchen. The flour in your recipe matters too: whole wheat and rye ferment faster than white. And ambient temperature shifts the timeline the moment your dough hits the counter.

The ratio also scales, roughly. Got a recipe with 14g of instant yeast? You'd reach for somewhere around 200g of starter as a starting point. The match isn't strict, since once you're on sourdough, schedule and inoculation percentage matter more than preserving a yeast-equivalent number. Pick a starter amount that fits the timing you actually want.

One thing to nail down before you proceed: your starter's hydration. A 100% hydration starter is fed equal parts flour and water by weight. That's the assumption behind these ratios, and it's the most common home-baker setup. If yours is different, the flour and water math in the next section changes. You can check what hydration your starter is kept at over on the starter guide.

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yeast-to-starter converter with fields for yeast type, yeast amount, and starter hydration percentage

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Why the "just swap it" advice fails you

Here's what most guides don't tell you: your starter is not free flour and water. It already contains both, and if you add it to your recipe without adjusting, your dough will be wetter than you planned.

A 100% hydration starter is, by definition, 50% flour and 50% water by weight. Add 100g of starter and you've added 50g of flour and 50g of water to your recipe before you've touched the bag of flour.

Skip that adjustment and your hydration drifts up. In the example below it's about three points higher than you intended. In recipes that lean on more starter, it's bigger. Three points doesn't sound like much, but it's enough to shift dough feel from manageable to slack and to flatten the loaf in the oven.

Before:

• 500g flour, 325g water, 7g instant yeast (65% hydration)

After, done wrong:

• 500g flour, 325g water, 100g starter added on top (you've now got an effective 68%+ hydration dough)

After, done right:

• 450g flour, 275g water, 100g starter (hydration stays at 65%)

That subtraction step is the most commonly skipped part of every sourdough conversion you'll find online.

Adjusting flour and water (the part most blogs skip)

Let's do the math properly.

If you're using 100g of 100% hydration starter, subtract 50g of flour and 50g of water from your recipe. That's it. Your starter contributes both, so you balance the recipe by taking both out.

Example:

• Original: 500g flour, 325g water, 10g salt, 7g instant yeast
• Converted: 450g flour, 275g water, 10g salt, 100g starter

The total flour weight is still 500g (450g in the bowl + 50g in the starter). Same with water. Your recipe is structurally identical, just fermented differently.

What if your starter isn't 100% hydration?

The formula is the same idea, just slightly different numbers. For a stiff starter at 60% hydration, 100g of starter is about 62.5g flour and 37.5g water. So you'd subtract 62.5g flour and 37.5g water from the recipe. A rye starter or any higher-hydration starter just shifts those proportions accordingly.

If you want to see exactly how the numbers work for your setup, the baker's percentage guide covers the underlying math. Or skip the manual arithmetic entirely:

Calculator

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full recipe converter that takes a yeasted recipe and outputs the adjusted sourdough version with corrected flour and water amounts

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One quick note on scaling. If a recipe calls for more yeast than 7g and you're adding more than 100g of starter, the flour and water subtraction scales with it. Adding 200g of starter means subtracting 100g flour and 100g water. It stays proportional.

Timing is the real conversion

This is where people get caught off guard. You've done the math perfectly, the dough is mixed, and then... it just sits there.

Commercial yeast dough rises in 1–2 hours. Sourdough wants 4–12 hours, sometimes more. That's not a bug. It's the whole point. Longer fermentation builds flavor, improves digestibility, and develops the gluten differently.

The mistake is watching the clock instead of the dough. Learn to read the dough, not the timer. A properly fermented bulk rise will feel pillowy and full of gas when you press it gently. It'll have grown by 50–75% in most recipes. The exact time to hit that point depends on your starter strength, your kitchen temperature, and the flour you used.

A few things that help:

• Use a straight-sided container for bulk fermentation. You can actually see the rise instead of guessing.
• A cold retard is your friend. After shaping, put the dough in the fridge overnight. It slows fermentation way down, makes scheduling flexible, and often improves flavor. Bake it straight from cold in the morning.
• Don't panic if it's slow. Slow fermentation at cooler temps usually produces better-tasting bread than a rushed warm proof.

The side-by-side difference is real: a yeasted sandwich loaf might be done start-to-finish in 4 hours. The sourdough version of the same loaf? Plan for 14–18 hours, most of which is hands-off.

Temperature matters way more now

Commercial yeast is forgiving. It works reasonably well anywhere from about 65°F to 80°F (18°C to 26°C). Your starter is pickier.

Below 65°F (18°C), fermentation slows dramatically. A dough that would bulk in 5 hours at 76°F might take 10–12 hours in a 62°F kitchen. That's not a disaster, but it catches people off guard.

Target dough temperature matters. Most sourdough bakers aim for a finished dough temp right around 75–78°F (24–25°C). If your kitchen is cool, use slightly warmer water. If it's summer and your kitchen is 80°F, use cooler water. A cheap instant-read thermometer is one of the most useful tools you can have for this.

A few practical adjustments:

• Winter doughs: Warm your water more than usual. Put the dough somewhere cozy, like near the oven or on top of the fridge.
• Summer doughs: Use cold water. Fermentation will move fast, so keep an eye on the dough.
• Consistent spot: Find one place in your kitchen that holds a predictable temperature and use it every time. It makes your results much more repeatable.

The starter guide has more on reading your starter's activity, which is the other half of understanding your fermentation speed.

When you shouldn't convert (or should hedge)

Some recipes don't take well to a full sourdough conversion. Enriched doughs are the main ones to watch. Brioche, hamburger buns, cinnamon rolls, and similar recipes have high amounts of butter, eggs, and sugar. Those ingredients slow fermentation significantly, and starter-only enriched doughs can take 18–24 hours to proof, with unpredictable results.

It's not impossible, but it's genuinely hard to get right, especially if you're just starting to convert recipes.

The hybrid approach is worth knowing about. Use half the yeast called for in the recipe and add about 10% starter (10g of starter for every 100g of flour). You get some sourdough flavor and tang, a more manageable rise time, and a gentler introduction to sourdough baking without completely removing the safety net of commercial yeast. Scaling stays clean because the starter inoculation is tied to flour weight, not a fixed gram amount.

This is also a good strategy when you want to convert a recipe but your starter is young or you're not confident in its strength yet. Half-and-half gives you margin for error.

When sourdough-only doesn't make sense:

• Recipes with more than 15% butter or fat by flour weight
• Recipes with more than 10% sugar
• Anything that needs a predictable short proof time (dinner rolls for tonight, for example)

Worked example: a 500g yeast loaf, converted

Let's convert a basic white loaf from start to finish.

Original yeasted recipe:

• 500g bread flour
• 325g water
• 10g salt
• 7g instant yeast

Converted sourdough recipe:

• 450g bread flour
• 275g water
• 10g salt
• 100g active 100% hydration starter

The math: 100g starter contributes 50g flour and 50g water. Subtract both from the original recipe. Total flour in the dough stays 500g. Total water stays 325g. Salt doesn't change.

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Pre-filled with the example above: 500g flour, 65% hydration, 100g starter at 100% hydration.

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The timeline, side by side:

The sourdough loaf takes longer, but most of that time is hands-off. The active work time is nearly identical. You're just planning further ahead.

A few notes on the conversion itself:

• Feed your starter 4–8 hours before mixing. You want it at peak activity, when it's domed and full of bubbles.
• Don't skip the autolyse if you usually do one. With longer fermentation, gluten development from rest becomes even more valuable.
• Taste the difference. The converted loaf will have a mild tang and a slightly more complex crumb. That's the whole point of going through this.

Want to plug in your own recipe instead? The recipe calculator handles the full conversion.

Common things that go sideways

Dough too wet. Almost always means the flour and water subtraction got skipped. Go back, check the math. If the dough is already mixed and too sticky, you can add flour a little at a time during the first few folds.

Dough barely rises. Two likely causes. First: the starter wasn't at peak activity when you mixed. It should be domed, airy, and at least close to doubling after a feed before you use it. Second: the kitchen is too cold. If it's below 68°F (20°C), find a warmer spot or give it more time. Check how to test your starter's strength if you're not sure it's ready.

Dense crumb after baking. Usually underproofing, not overproofing. People assume they've gone too far, but most home bakers stop too early. The poke test helps: press a floured finger into the shaped dough. It should spring back slowly, about halfway. If it springs back instantly, it needs more time.

Bread tastes flat, no tang. Either the starter is weak, the fermentation was too short, or both. A longer cold retard adds flavor. A stronger starter adds reliability. Both help.

Overproofed and collapsed. This happens, especially in hot kitchens. If the dough springs back at all when you poke it, you still have time. If it doesn't spring back, get it in the oven immediately, even if it's earlier than you planned. A slightly overproofed loaf baked fast is better than one left to deflate completely.

The converted recipe just feels harder than it should. That's normal at first. Once you understand three things, it gets much easier: how much starter to use, how to subtract its flour and water, and how to follow the dough instead of the clock. That's really the whole game.

Here's what to try next

Pick the simplest yeasted recipe you already trust. Not brioche. Something lean, like a basic white loaf or a weeknight pizza dough.

Run it through the calculator, write the new numbers on the recipe card so you're not redoing math mid-bake.

Bake it on a weekend so the timing doesn't stress you out.

The second bake is always better than the first. By then, you know how your starter behaves in that dough.