Sourdough Starter Feeding Calculator
Starter and feeding inputs
Use 100% if starter contains equal flour and water by weight.
The target must have room for all flour and water already present in the retained starter.
Feeding results
Feeding schedule
| Feed | Feeding time | Estimated peak |
|---|---|---|
| 1 | — | — |
| 2 | — | — |
| 3 | — | — |
Times use this device's local time zone. Look for your starter's actual rise, bubbles, aroma, and dome rather than relying only on the clock.
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How to Calculate a Sourdough Starter Feeding
- Weigh the starter you will retain. Discard or use the rest, then enter only the amount remaining in the jar.
- Enter its current hydration. A starter made with equal flour and water by weight is 100% hydration.
- Choose ratio or target mode. Ratio mode scales flour and water from the retained starter. Target mode works backward from a required final amount and hydration.
- Mix the calculated additions. Use a scale and keep the selected weight unit consistent for every input.
- Plan from observed behavior. Enter how long this starter usually takes to peak under your current conditions, then use the schedule as a reminder rather than a guarantee.
Sourdough Feeding Ratios Explained
A ratio such as 1:2:2 means one part retained starter, two parts flour, and two parts water, all by weight. With 20 g starter, the feed is 40 g flour plus 40 g water, producing 100 g total starter.
The first number is not an extra ingredient: it is the starter already in the jar. Changing every part by the same factor does not change the ratio. A 2:4:4 feeding is mathematically identical to 1:2:2.
| Ratio | With 20 g retained starter | Relative refresh |
|---|---|---|
| 1:1:1 | Add 20 g flour + 20 g water | Smaller feed |
| 1:2:2 | Add 40 g flour + 40 g water | Moderate feed |
| 1:5:5 | Add 100 g flour + 100 g water | Larger feed |
A larger refresh often changes peak timing, but there is no universal hours-to-peak conversion. Culture activity, flour, water, and temperature all matter.
Starter Hydration Formula
Hydration compares water with flour, not water with total starter weight. The calculator first separates the retained starter into its existing flour and water, then adds the new feed.
Existing flour = retained starter ÷ (1 + current hydration ÷ 100)
Existing water = retained starter − existing flour
Final hydration = total water ÷ total flour × 100
Example: 20 g of 100% hydration starter contains 10 g flour and 10 g water. A 1:2:1 feeding adds 40 g flour and 20 g water. The final starter has 50 g flour and 30 g water, so its hydration is 60%.
Target mode uses the same equations in reverse. If the retained starter already contains more flour or water than the requested final build permits, the calculator stops and explains how to make the target feasible.
How to Use the Feeding Schedule
Starter activity cannot be predicted from ratio alone. Instead, the schedule planner uses your observed time to peak and adds it to each planned feeding time. If your starter normally peaks about eight hours after a 1:2:2 feed in your kitchen, enter 8 hours. Update that number when the flour, room conditions, or feeding ratio changes.
For a bake, many bakers aim to use starter while it is active and near its usual peak. The visual state is more useful than a timestamp: compare rise, bubbles, surface shape, and aroma with previous successful feeds.
Frequently Asked Questions
What does a 1:2:2 sourdough feeding ratio mean?
It means one part retained starter, two parts flour, and two parts water by weight. For 20 g of starter, add 40 g flour and 40 g water.
How is starter hydration calculated?
Divide the total water by the total flour and multiply by 100. This tool includes the flour and water already present in the retained starter.
Why can a target starter build be impossible?
The retained starter may already contain more flour or water than the requested build allows. Retain less starter, increase the target weight, or choose a target hydration closer to the current starter.
Does a feeding ratio predict exactly when starter will peak?
No. Peak time also depends on culture strength, flour, water, and temperature. The schedule uses the hours-to-peak value you provide from your own observations.
Can I use ounces?
Yes. Choose ounces and keep all weights in ounces. The ratio and hydration math is unit-independent as long as every weight uses the same unit.
Are my starter details stored?
No. Calculations run locally in your browser. Copying or downloading a plan happens only when you choose that action.