Fermentation Calculators
Track fermentation timing, plan diacetyl rests, cold crashes and conditioning schedules.
Fermentation Time Calculator
Estimate primary and secondary fermentation duration for your beer.
Diacetyl Rest Calculator
Calculate timing and temperature for a diacetyl rest in lagers.
Cold Crash Calculator
Calculate cold crash timing and temperature for clear beer.
Secondary Fermentation Calculator
Determine if and when to transfer to secondary fermentation.
Bottle Bomb Calculator
Check if your beer is safe to bottle based on gravity readings.
Lag Time Calculator
Estimate yeast lag time based on pitch rate, temperature and viability.
Temperature Control Calculator
Calculate heating or cooling needs for fermentation temperature control.
Fermentation Log Calculator
Track and analyse gravity readings over your fermentation period.
8 free calculators in Fermentation
Understanding Fermentation in Homebrewing
Fermentation is where your wort becomes beer, and managing it well is the single biggest factor in producing clean, flavourful homebrew. For UK brewers working in unheated garages or spare rooms, ambient temperatures can swing significantly with the seasons — from below 10°C in winter to above 25°C during a summer heatwave. The temperature control calculator helps you work out whether you need a heat belt, brew fridge or simple insulation wrap to keep your fermentation in the yeast's ideal range. The fermentation time calculator gives you a realistic timeline for primary fermentation, which typically runs five to ten days for a standard-strength bitter or pale ale.
If you are brewing lagers — and British-brewed lagers are growing in popularity at CAMRA festivals and homebrew competitions alike — the diacetyl rest calculator is essential. Diacetyl produces an unwanted buttery off-flavour, and a well-timed rest at 18-20°C near the end of primary fermentation allows the yeast to reabsorb it. Follow this with a cold crash using the cold crash calculator to drop yeast and proteins out of suspension for brilliantly clear beer.
Safety matters too. The bottle bomb calculator checks whether your final gravity has truly stabilised before you bottle, preventing dangerous over-carbonation. Track your gravity readings over time with the fermentation log calculator — consistent readings over two to three days confirm fermentation is complete. The lag time calculator is useful for diagnosing slow starts, helping you determine whether a sluggish fermentation is down to underpitching, low viability or cool temperatures.