Sourdough Calculator — Hydration and Baker's Percentages
This sourdough calculator works out the flour, water, salt and starter for your bread from the number of loaves, their weight and your target hydration, splitting the starter's flour and water with no double counting. A theoretical schedule places bulk fermentation, final proof and cold retard within your day.
Calculated results
Schedule
- Start (autolyse/mixing) : 08:00
- End of bulk fermentation : 12:00
- End of final proof : 14:00
- Out of the fridge : 02:00 (next day)
- Bake after returning to room temperature
The schedule shows the theoretical times of each step, not biological readiness: actual fermentation depends on temperature and starter activity.
Method and limits
How to use this calculator
Start with the number of loaves and their target weight, then enter hydration and salt as baker's percentages. Give the starter percentage and its actual hydration — 100% for a balanced starter, lower for a stiff one — so the starter's flour and water are split correctly. Finish the timeline with the start time, the bulk fermentation and final proof durations, and the cold retard if you use one.
With M the total dough mass, h the hydration, s the salt, r the starter percentage and q the starter hydration: total flour is F = M / (1 + h + s), the starter's flour is F_starter = r × F / (1 + q) and its water W_starter = q × F_starter; the flour and water to add follow by subtraction. The schedule simply adds the durations you enter — it is time organization, not a prediction of biological readiness.
Mass balance with no double counting
Every flour figure includes the flour inside the sourdough starter — the convention that prevents the most common accounting mistake in naturally leavened bread. Given the target dough mass, flour, water and salt are derived in an exact balance, conserved to the gram before display rounding. If the starter brings in more water than the recipe allows, an explicit error offers both fixes: raise the target hydration or lower the starter percentage.
A theoretical schedule
The timeline starts at your start time and adds durations: end of bulk fermentation, end of final proof, and out of the fridge when the cold retard is enabled, midnight rollovers included. Room temperature tunes the warnings — above 26 °C (79 °F) fermentation runs faster, below 18 °C (64 °F) it runs slower — but never turns the clock into a prediction. A starter percentage of zero is flagged: the recipe then relies on the naturally present yeasts alone.
Worked example
For 2 loaves of 800 g at 75% hydration, 2% salt and 20% starter at 100% hydration: total mass 1,600 g, giving 903.95 g total flour, 677.97 g water and 18.08 g salt. The starter to set aside weighs 180.79 g (90.40 g flour + 90.40 g water), leaving 813.56 g flour and 587.57 g water to add. Starting at 08:00 with 4 h of bulk fermentation, 2 h of final proof and 12 h of cold retard: bulk ends at 12:00, final proof at 14:00, and the loaves come out of the fridge at 02:00 the next day. Reproduce these values in the tool: you must get exactly the same results.
Assumptions and limits
Percentages are baker's percentages, taken on total flour including the starter's flour. The schedule is purely additive: it does not predict actual fermentation, which depends on temperature, starter activity, flour strength and hydration. The accepted ranges (hydration 45–100%, salt 0–4%, starter 0–100%, cold retard 0–48 h) cover common recipes; boundary values trigger warnings rather than blocks, except where the math itself is impossible — a starter bringing in more water than the recipe allows.
Frequently asked questions
Limits of use