Add the starter needed for the recipe to the amount you want to keep, then divide that target by the feeding ratio’s total parts.
- Reserve belongs inside the target build.
- Allow for the practical precision of your scale.
- Record losses rather than pretending a bowl empties perfectly.
Start with the amount the recipe will use
The useful starting number is the weight of ripe starter or levain that will go into your dough. Read the ingredient list and the preparation steps together. A recipe may list a levain build separately and later ask you to use all of it, or it may tell you to make more than the dough requires. Copy the actual amount used in the final dough onto your plan. Do not automatically treat every gram in a preferment jar as part of the bread formula.
Next decide how you will keep your culture for future baking. You can retain a portion of this build or maintain a separate jar. Both arrangements can work as an organizational system, but they produce different target quantities. A retained reserve belongs in the build total. A separate maintenance jar already exists outside that total. This guide uses arithmetic examples to show the distinction; it does not prescribe a universal starter size or a fixed time to ripen.
Separate three quantities that sound similar
Seed is the existing starter you use to begin a build. Fresh feed is the new flour and water. Finished build is their combined mass immediately after mixing. If you mix 20g seed, 80g flour, and 80g water, the fresh additions weigh 160g and the complete build weighs 180g. Saying 'I fed 180g' is ambiguous because it could mean either that you added 180g of ingredients or that you made a 180g total mixture.
Use explicit labels whenever you write a shopping list, share a feeding plan, or enter values into a calculator. A target field should mean the complete mixed quantity; a seed field should mean what you already have. This also explains why feeding every bit in a large jar can create much more starter than expected. At 1:2:2, 100g existing starter becomes a 500g build after adding 200g each flour and water. The arithmetic multiplies the seed weight by five.
Work backward from the target
For a feeding ratio written seed:flour:water as a:b:c, divide the target build by a+b+c to find one part. Multiply that result by each number. A 150g target at 1:2:2 gives 30g seed, 60g flour, and 60g water. A 180g target at 1:4:4 gives 20g, 80g, and 80g. These are scaling calculations. They do not assess whether the available starter is active enough for your chosen recipe.
If you already know the seed weight, calculate forward instead. At 1:4:4, a 12g seed receives 48g flour and 48g water for a 108g total. That build cannot supply a recipe needing 200g plus a reserve. You could make a larger build from a larger amount of suitable seed, or plan a sequence of refreshments. Avoid quietly changing the ratio by adding arbitrary flour and water while continuing to use the original label.
Example: 200g for dough and 20g to retain
Suppose your recipe needs 200g levain and you want 20g left afterward. Your target is 220g. At 1:4:4 there are nine parts, so the calculated seed is 220 ÷ 9 = 24.444g. Each fresh addition is four times that amount, or 97.778g flour and 97.778g water. These displayed numbers sum to 220g. They assume a simple mass balance before fermentation, evaporation, and handling losses.
On a whole-gram scale, 24g seed plus 98g flour plus 98g water is a practical 220g approximation. When ready for the recipe, transfer 200g into the dough and retain the intended remainder. If your jar and utensils usually retain several grams, plan an explicit extra allowance instead of assuming you will recover every trace. For example, a 225g build can allocate 200g to dough, 20g to the next refreshment, and 5g as a handling allowance. That allowance is your planning choice, not a measured universal loss.
| Allocation | Weight | What it means |
|---|---|---|
| Dough requirement | 200g | The portion weighed into the recipe |
| Retained reserve | 20g | The portion planned for ongoing maintenance |
| Target build | 220g | Seed plus all fresh additions before losses |
Keep a reserve you can actually maintain
A reserve is useful only if you know what happens to it next. Write down where it will go, how it will be refreshed, and which maintenance method you follow. Keeping a random scraping in an unlabeled jar makes it difficult to reconstruct its feeding ratio or hydration. Keeping an enormous amount simply because the recipe made extra can produce unnecessary additions at the next feed. Decide the maintenance quantity deliberately rather than letting leftovers choose it for you.
King Arthur's maintenance recipe distinguishes routine culture care from preparing a larger quantity for baking. That separation is useful even if your own amounts differ from theirs. Your maintenance culture is a continuing ingredient supply; the baking build is a batch with a destination. Labeling them separately helps prevent the common mistake of pouring the entire culture into dough. Before the final transfer, physically identify the jar or portion that will remain.
Know which hydration your recipe expects
At 100% hydration, starter contains equal masses of flour and water under the usual ingredient-accounting model. Thus 200g starter contributes 100g flour and 100g water to the dough. A 200g portion at 50% hydration instead contains approximately 133.33g flour and 66.67g water. Both weigh 200g, but replacing one with the other changes the final dough. The starter's name or feeding frequency does not tell you that composition; its flour and water history does.
For seed weight S and hydration h expressed as a decimal, seed flour is S ÷ (1+h), and seed water is S × h ÷ (1+h). Add the new flour and water to those contributions before calculating the final build hydration. Equal fresh flour and water preserve 100% hydration only when the seed is already at 100%. If you are changing from a stiff culture to a liquid levain, plan that conversion explicitly and check the recipe quantities afterward.
Do not count levain flour twice
Imagine a dough intended to contain 500g total flour and 350g total water, including its levain. With 200g of 100% hydration levain, 100g of each ingredient already arrives inside the levain. The final mixing additions are therefore 400g flour and 250g water, plus the other ingredients specified by the formula. This is a calculated example, not a complete bread recipe or a recommended fermentation schedule.
Now consider a recipe that says '500g flour, 350g water, 200g starter' without defining those as total quantities. If those are all final-mix additions, the complete dough contains 600g flour and 450g water. Its overall hydration is 75%, not 70%. The same displayed ingredient numbers can describe different accounting conventions. Read the method, look for an overall formula, and retain the original recipe's convention when scaling. King Arthur's professional baker's-percentage reference explains why preferment ingredients must be included when calculating overall percentages.
Plan more than one loaf without losing track
For two identical loaves that each require 100g levain, the dough requirement is 200g. If you are making them together from one build, add a single reserve, not one reserve for every loaf unless you intentionally want separate cultures. Two 100g portions plus a 20g reserve again call for 220g before any handling allowance. Multiplying the whole one-loaf maintenance plan by two would accidentally double the reserve as well.
For different recipes, list the needs separately. A hypothetical Saturday loaf requiring 120g and another requiring 180g create a 300g dough requirement if their mixing windows and levain specifications are compatible. Add the reserve afterward. If one recipe requires a stiff preferment and the other a liquid one, a shared total is not enough information. Prepare separate labeled builds, or follow a documented conversion. Quantity planning should preserve each recipe's ingredient composition and intended stage.
Use staged builds for a reason
Sometimes the amount of suitable seed you have is too small for the build you want at your chosen ratio. A staged plan can bridge that gap. As a purely numerical example, 10g seed at 1:2:2 makes 50g mixed starter. Taking 30g of an appropriately developed build into another 1:2:2 refreshment makes 150g. The unused portion needs its own destination. These numbers show a sequence of quantities, not a promise that both refreshments will be ready within one day.
Each stage introduces another readiness decision, jar, and opportunity for a weighing error. For that reason, do not add stages merely because a calculator can generate them. Start earlier when your culture needs preparation, follow a reliable maintenance method, and observe the response before committing the final build to bread. A sequence is particularly difficult to plan when you do not yet know how your starter behaves under the conditions you will use.
Reduce surplus at the planning stage
Repeatedly making a large maintenance batch and then looking for recipes to consume it can turn a simple hobby into a disposal problem. Start by reviewing how much ripe starter you actually use in a typical bake. Then choose a manageable maintenance routine that can produce that amount when needed. Small amounts are not automatically better: a batch too small for your scale or jar can be harder to measure and observe. Aim for deliberate, repeatable quantities.
Keep 'extra starter' and 'ingredient that a discard recipe specifically accepts' separate in your notes. A recipe requiring ripe starter relies on a different condition from a recipe written for unfed discard, possibly with another leavening ingredient. Do not substitute leftovers solely because the weights match. Also avoid building more starter simply to compensate for uncertainty about ripeness; more grams do not solve a culture that has not developed as expected.
Check the plan before you feed
Read the final plan as if you were handing it to someone else: recipe amount, reserve amount, optional handling allowance, target total, ratio order, seed hydration, and actual gram weights. Check that the three ingredient weights sum to the intended build. Check that the starter requirement in the dough is not being added twice. Finally, label the jar with its purpose and note when you expect to start observing it, without treating that expectation as a readiness guarantee.
A useful final note is the actual amount recovered when you transfer the levain. If you consistently make 220g but can only divide out 215g, the next plan can account for your handling method. If you consistently have far more remaining than intended, review your targets before changing feeding ratios. This closes the loop between calculator arithmetic and kitchen practice while preserving a clear distinction between calculated quantities and observed results.
Sources & further reading
This guide combines published references with our own explanations and decision aids. Numerical examples are illustrative; they are not records of Sourdough Bench test bakes.
Put it into practice.
Keep the recipe, observations and next change together in your downloadable bake log. For a symptom-led starting point, use the loaf troubleshooting guide.