Sourdough Discard Calculator: How Much to Keep and Feed
On this page
Every feeding of a starter at a fixed amount involves the same arithmetic. You hold a certain weight of starter, keep a small part of it, discard the rest, and feed what you kept with flour and water. The feeding ratio decides how small the kept part is. This calculator gives the grams, and the flour a week of feedings uses.
The math
Add up the ratio parts: one part = amount you hold ÷ (starter part + flour part + water part).
- Keep = one part × starter part
- Flour = one part × flour part
- Water = one part × water part
- Discard = amount you hold − keep
Weekly flour = flour per feeding × feedings per week.
Worked examples
Holding 100 g of starter after each feeding, fed daily (7 feedings a week):
| Ratio | Keep | Discard | Flour | Water | Flour per week | Discard per week |
|---|---|---|---|---|---|---|
| 1:1:1 | 33.3 g | 66.7 g | 33.3 g | 33.3 g | 233 g | 467 g |
| 1:2:2 | 20 g | 80 g | 40 g | 40 g | 280 g | 560 g |
| 1:5:5 | 9.1 g | 90.9 g | 45.5 g | 45.5 g | 318 g | 636 g |
A higher ratio keeps less old starter, so more is discarded and a little more flour is used at each feeding.
Using less flour
The way to waste less is to hold less starter, feed less often, or use the starter in your baking. If a recipe calls for starter, take it from the amount you hold before discarding. Work out how much a recipe needs with how much starter to use, and keep that much extra with the feeding ratio calculator. This site gives no recipes for discard.
Sources
- Arithmetic of the feeding ratio (parts by weight). All numbers above are computed with it.