For most home loaves, 20% starter is the sensible default. In mostly white flour at around 24 °C (75 °F), it finishes bulk fermentation in roughly five to six hours, which fits a normal day. Drop to 10% when you want a slower, longer ferment, such as an overnight bulk or a hot kitchen. Go up to 30% when your kitchen is cool or you need the dough to move faster. The percentage is the weight of ripe starter compared with the total flour, so 20% of 500 g of flour is 100 g of starter.
The amount you choose doesn’t make the bread better or worse on its own. It changes how fast things happen, and that in turn nudges flavour and handling.
What the percentage measures
Starter amounts are written as a share of the flour. The tools on this site count the flour inside the starter as part of the total flour, which is the most common convention. Some books measure the starter against the added flour only, so the same recipe can look like 20% in one place and 22% in another. The difference is small at these levels, but it’s worth knowing which one a recipe uses. Baker’s percentages explained simply covers both conventions.
Whichever convention you follow, the starter brings its own flour and water. A 100% hydration starter is half flour and half water, so changing the starter amount changes how much flour and water you add separately.
Three amounts, one loaf
To see the effect, take one 900 g loaf at 72% hydration with 2% salt and a 100% hydration starter, and change only the starter percentage. The sourdough recipe builder gives:
| Ingredient | 10% starter | 20% starter | 30% starter |
|---|---|---|---|
| Starter | 52 g | 103 g | 155 g |
| Flour to add | 491 g | 466 g | 440 g |
| Water to add | 347 g | 321 g | 295 g |
| Salt | 10 g | 10 g | 10 g |
| Share of flour prefermented | 5% | 10% | 15% |
The total flour stays at 517 g and the total water at 372 g in all three, so the hydration doesn’t move. Only the split between starter and fresh ingredients changes. That’s the point of letting a calculator do it: adding extra starter on top of an unchanged recipe would make the dough wetter as well as faster.
How long each one takes
Here the differences become practical. The bulk fermentation time estimator gives these ranges for mostly white flour:
| Starter | Dough at 21 °C (70 °F) | Dough at 24 °C (75 °F) |
|---|---|---|
| 10% | about 8 h to 11 h | about 6 h to 8 h |
| 20% | about 6 h 15 min to 8 h 30 min | about 4 h 45 min to 6 h 15 min |
| 30% | about 5 h 15 min to 7 h 15 min | about 4 h to 5 h 15 min |
Two things stand out. First, tripling the starter doesn’t cut the time by two-thirds. At 24 °C, going from 10% to 20% saves about an hour and a half, and going from 20% to 30% saves only about another hour. Second, three degrees of dough temperature shift the time about as much as a big change in starter. Temperature is the stronger lever, and starter is the fine adjustment.
Treat the estimates as a window for checking the dough, not as a timer. Your starter’s strength and your flour both move the real figure.
What changes besides time
Flavour
Starter carries acid into the dough, so a higher percentage gives a dough that starts out more acidic. A low percentage over a long, slow ferment can end up just as tangy, though, because the bacteria have more hours to work. The other levers that shape the flavour are covered in what makes sourdough too sour or too mild.
Strength and handling
Acid and enzymes from the starter slowly soften gluten. At 30% and above, a dough can feel slack and sticky toward the end of bulk, especially in a warm kitchen. At 10%, the gluten has more time to strengthen through folds before the acidity builds, and the dough often feels more elastic.
Forgiveness
A fast dough has a short window when it is at its best. With 30% starter in a warm room, the gap between ready and overproofed can be under an hour. A 10% dough drifts slowly through that stage, which makes it easier to catch.
Choosing an amount for your day
- 10% or a little less: overnight bulks in a cool room, summer baking, or any day when you won’t be home to check the dough. Sourdough in hot weather goes further into slowing a fast dough.
- 15 to 20%: a normal daytime bake at 22 to 25 °C, mixed late morning and shaped by late afternoon.
- 25 to 30%: a cold kitchen in winter, or a dough with ingredients that slow fermentation, such as plenty of sugar or butter. Sourdough in a cold kitchen has more ways to keep a dough moving.
If you want to change a recipe you already like, keep its hydration and salt, set the new starter percentage in the recipe builder, and let it rebalance the flour and water.
A strong starter matters as much as the amount
Every timing in this post assumes a lively starter used near its peak. A starter that takes ten hours to double, or one used long after it has collapsed, behaves as if you had used much less of it. Bakers often respond by adding more, and end up with a dough that is both slow and sour.
Before you change the percentage, check that the starter rises predictably after a feed, at least doubling in the time you expect for your ratio and temperature. If it doesn’t, a few days of regular feeding in a warm spot will do more for your bread than any change in the recipe.
The opposite also applies. A very vigorous starter, especially one fed with some whole grain flour, can make 20% behave like 30%. Your own notes are the best guide: write down the percentage, the dough temperature and how long bulk took, and after three or four bakes you will know how your starter compares with the estimates.
Common starter-amount mistakes
- Adding more starter without adjusting the rest. The dough ends up wetter than the recipe intended. Take the starter’s flour and water out of the separate amounts.
- Expecting more starter to fix a weak starter. A sluggish culture is slow at any amount. Get it rising predictably first.
- Changing starter and temperature at once. You won’t know which change did what. Adjust one at a time.
- Following the recipe’s hours with a different percentage. If you halve the starter, the bulk takes longer. Recalculate the window before you start.
Starter amount questions
Does more starter make the loaf rise higher?
Not by itself. Height comes from gluten strength, shaping and ending fermentation at the right point. More starter only gets the dough to that point sooner. A loaf with 10% starter can rise just as tall if it is given enough time.
Can I go below 10%?
Yes. Bakers use 2 to 5% for very long ferments, such as a bulk that runs through a warm night. The timing becomes harder to predict, so check the dough in the morning rather than trusting the clock, and keep the starter strong.
Should the starter percentage change with whole grain flour?
Often it can come down a little. Whole wheat and rye ferment faster than white flour, so a dough with a large whole grain share may reach the end of bulk sooner at the same percentage. Start checking earlier and adjust next time.