Sourdough Starter Calculator
Calculate feeding amounts, discard quantities, and build the perfect levain for baking day. Adjustable hydration and ratios.
Quick Answer
For a standard loaf using 500g flour at 100% hydration, you need about 100g of active starter (20% of flour weight). To build that levain, mix roughly 9g seed starter + 45g flour + 45g water the night before. Feed your maintenance starter at a 1:5:5 ratio, discarding down to about 9g before each feeding.
100% = equal parts flour and water by weight
Typical range: 15-25%. Lower = slower ferment, more sour.
Levain Build for Baking Day
Night-Before Levain Build (1:5:5 ratio)
Mix 9g seed starter + 45g flour + 45g water = 99glevain. Let it ferment 8-12 hours at room temperature until doubled and bubbly. It's ready when a small amount floats in water.
Adjusted Dough Formula
Subtract the flour & water already in the levain from your recipe totals.
Daily Maintenance Feeding (100g jar)
Baker's Tips
- The float test: drop a spoonful of levain in water. If it floats, it's ready.
- Warmer temps (78-82F) speed up fermentation; cooler temps slow it down
- Use discard for pancakes, crackers, pizza dough, or banana bread
- Store inactive starter in the fridge and feed once a week to maintain
- Whole grain flours ferment faster than white flour due to more wild yeast
About This Tool
The Sourdough Starter Calculator takes the math out of sourdough baking by computing exact feeding amounts, levain builds, and discard quantities based on your recipe's flour weight, desired hydration, and preferred feeding ratio. Whether you're a beginner building your first starter or an experienced baker scaling a recipe, this tool ensures you always have the right amount of active levain ready for baking day.
What Is a Sourdough Starter?
A sourdough starter is a living culture of wild yeast and lactic acid bacteria maintained by regular feedings of flour and water. Unlike commercial yeast, which is a single strain of Saccharomyces cerevisiae, a sourdough starter contains a diverse ecosystem of wild yeasts (primarily Kazachstania humilis and various Saccharomyces species) along with Lactobacillus bacteria that produce the characteristic tangy flavor. This symbiotic community has been used to leaven bread for at least 5,000 years, predating commercial yeast by millennia. The bacteria produce lactic and acetic acids that not only create flavor but also naturally preserve the bread, break down phytic acid (making minerals more bioavailable), and partially digest gluten proteins, which is why some people with mild gluten sensitivity find sourdough easier to digest.
Understanding Hydration
Hydration is expressed as a baker's percentage: the weight of water relative to the weight of flour. A 100% hydration starter contains equal parts flour and water by weight (not volume), producing a thick, pancake-batter-like consistency. This is the most common and easiest to maintain. A 75% hydration starter is stiffer, more like a dough ball, and tends to produce a more sour flavor because the drier environment favors acetic acid-producing bacteria. A 125% hydration starter is more liquid and ferments faster. Most recipes assume 100% hydration, and this calculator defaults to that, but you can adjust it to match your specific starter's hydration level for accurate flour and water calculations.
Feeding Ratios Explained
A feeding ratio like 1:5:5 means 1 part seed starter to 5 parts fresh flour to 5 parts water by weight. Higher ratios (like 1:10:10) give the yeast and bacteria more food, extending the time until the starter peaks and producing a milder flavor. Lower ratios (like 1:1:1) peak quickly and develop a stronger sour flavor because the existing acids aren't as diluted. For levain builds the night before baking, 1:5:5 is a reliable ratio that peaks in about 8-12 hours at room temperature (70-75 degrees Fahrenheit). In warmer climates or during summer, you might use a higher ratio like 1:8:8 to prevent the levain from peaking too early and collapsing before you mix your dough.
The Levain Build
A levain (also called a leaven or pre-ferment) is a portion of starter that you build specifically for a bake. Rather than dumping your entire maintenance starter into the dough, you take a small amount of seed starter and feed it fresh flour and water in the exact quantity your recipe needs. This serves two purposes: it ensures your levain is at peak activity when you mix your dough, and it preserves your mother starter for future bakes. The calculator computes the exact amounts of seed starter, flour, and water needed for your levain based on your recipe's flour weight and your chosen starter percentage. It also calculates the adjusted flour and water for your final dough, subtracting what's already in the levain so your overall hydration stays accurate.
Managing Discard
Every feeding produces discard, the portion of old starter you remove before adding fresh flour and water. This is necessary because without discarding, your starter would grow exponentially with each feeding. A 100g starter fed at 1:5:5 would become 1,100g after just one feeding without discarding. The discard is still full of flavor and can be used immediately in recipes that don't rely on leavening power: sourdough pancakes, waffles, crackers, pizza dough, flatbreads, and even chocolate cake. Many bakers keep a "discard jar" in the refrigerator, adding to it daily and using it throughout the week. This zero-waste approach makes sourdough baking both sustainable and versatile, giving you a steady supply of flavorful, fermented batter for quick recipes alongside your weekly bread bakes.