How this is calculated
Everything is derived backwards from the hour you set. The oven stages are fixed and predictable: a Dutch oven wants about forty-five minutes of preheat, the bake itself runs about forty-five minutes, and a loaf needs an hour on a rack before you cut it. Those are subtracted first.
Then the fermentation stages, which are not fixed at all. Yeast and bacterial activity roughly doubles for every 9°F (5°C) of warming and roughly halves for every 9°F of cooling — the same Q10 relationship that governs most enzymatic processes. The reference point used here is five hours of bulk at 76°F (24°C), at 20% inoculation, to a 75% rise. From there:
- Temperature. Bulk is multiplied by 2(76 − T)/9, with T in °F. At 67°F (19°C) that doubles it; at 85°F (29°C) it halves it. Switch the toggle at the top of the key and every temperature on the page, including the fields, becomes Celsius.
- Inoculation. More starter means a shorter lag and a faster climb, but not proportionally — doubling the starter cuts roughly a quarter off the time, not half. The model uses the square root of the ratio against 20%.
- Whole grain. Bran carries wild yeast and more available enzyme activity. A fully whole-grain dough runs about 30% faster than a white one; the adjustment is linear in between.
- Target rise. Getting to 50% takes less than two-thirds of the time it takes to reach 75%, because the early part of bulk is a lag phase with little visible change.
- Overnight cooling. If your bulk crosses the hours between 11pm and 6am and you have told the tool your kitchen drops, the temperature used is the average across the window, not the daytime figure.
If you choose a cold retard, shaped loaves go into the fridge and come out to be scored and loaded straight into the hot oven. Retard time is treated as a hold rather than as fermentation — it is not, entirely, but a shaped loaf at 38–40°F (3–4°C) ferments so slowly that treating it as a hold is closer to the truth than counting it as proof.
Worked example. Bread out of the oven at 7:00am Saturday, Dutch oven, twelve hours in the fridge, kitchen at 72°F (22°C), 20% starter, 20% whole grain, 65% target rise.
Subtract the 45-minute bake: the loaf goes in at 6:15am, so the oven goes on at 5:30am. Subtract twelve hours of fridge: shaped loaves went in at 6:15pm Friday. Subtract half an hour of settling and twenty-five minutes of bench rest: bulk ended around 5:20pm.
Bulk at 72°F ambient (22°C) — treated as 74°F dough — with 20% starter, 20% whole grain and a 65% target comes to about four hours fifty-five minutes. So you mix at roughly 12:25pm, and a 1:1:1 starter feed peaks about five and a quarter hours later, which puts the feed at around 7:10am Friday morning.
Reading the rise, not the clock
The number that matters is how far the dough has grown, not how long it has sat. Put a small sample in a straight-sided jar at mix, mark the level, and read the jar rather than the clock. The schedule below is a plan; the jar is the truth.
Alongside the jar: the dough should be domed rather than flat, jiggle as one mass when you shake the tub, and show a few bubbles at the surface and along the sides. If it has spread flat and gone slack, it has gone past the point this schedule was aiming at.
What this does not account for
- Your starter’s character. A young, sluggish or recently revived starter ferments far more slowly than a mature daily-fed one, and no temperature model can see that.
- Altitude. Above roughly 3,000 feet doughs proof faster and bake differently. Treat the bulk figure as an overestimate and watch the jar.
- Flour absorption and protein. A high-extraction or high-protein flour behaves differently from supermarket bread flour at the same hydration.
- Hydration. Wetter doughs ferment slightly faster and hold their shape for less time. This tool deliberately does not calculate hydration.
- Fridge temperature. A fridge at 34°F (1°C) and one at 42°F (6°C) are not the same retard. If yours runs warm, shorten the hold.
- Enriched doughs. Butter, egg, sugar and milk all change the timing and none of them are modelled here.
Common questions
What time do I start sourdough to bake in the morning?
With an overnight retard, usually around the middle of the previous day — you bulk through the afternoon, shape in the early evening, and the fridge does the waiting. Without a retard, an early morning bake means mixing in the small hours, which is why almost everyone baking at 7am is retarding.
Why does everyone say four to six hours?
Because at around 76–78°F (24–26°C), with a typical inoculation, that is roughly right. It is a true statement about one kitchen. In a 66°F (19°C) kitchen the same dough takes nine or ten hours, and the person following the four-to-six figure pulls an under-fermented loaf and blames their starter.
Do I have to measure dough temperature?
No. Dough sitting in a room settles within a degree or two of that room, and mixing adds a little friction warmth. Room temperature plus about two degrees is close enough to build a schedule on, and it is what most people can actually do. If you do own a thermometer, switch the toggle and use the real figure.
It is 2am and the dough has not risen. Now what?
Cover it and put the whole tub in the fridge, then go to sleep. Cold slows fermentation without stopping it, so an under-risen dough keeps working slowly overnight instead of either stalling or blowing past its target. In the morning, take it out, let it finish at room temperature, then shape and bake on a later schedule. A cold dough is recoverable; an over-proofed one is not.
Can I stretch the retard to eighteen hours?
Usually yes, if the dough was not already at the top of its bulk. Somewhere past eighteen hours the acidity climbs enough to weaken the gluten and the crust turns leathery. Twelve to fourteen is the comfortable range for most fridges.
Why is the starter feed so early?
Because a starter has to be at its peak when it goes into the dough, and a 1:1:1 feed reaches that peak in four to six hours at room temperature. If the feed time the tool gives you is inconvenient, change the ratio: a bigger feed peaks later, so 1:5:5 or 1:10:10 lets you feed the evening before instead of at dawn.
Does this work for a same-day bake?
Yes — switch the retard toggle to same day. The final proof at room temperature is then estimated at about 40% of your bulk time, which is the usual relationship, and the whole schedule collapses into one long day.
Are the times exact?
Deliberately not. Fermentation is a biological process with real variance, and a schedule printed to the minute invites you to trust the clock over the dough. The windows shown are roughly a tenth of the fermentation time either side, which is about as tight as anyone should claim.