Yeast Viability Calculator

Estimate the viability of your yeast and the number of viable cells from its manufacture date, type and amount.

Yeast type

Amount (mL)

At 1 billion cells per mL when fresh

Manufacture date

Printed on the package; fills in the days below

Days since manufacture (days)

Estimated viability88.7%Viable cells89billion cells

Results are estimates provided "as is," for informational and planning purposes only, without warranties of any kind. Check them before you rely on them: you are responsible for decisions about your beer and equipment, including pressure and carbonation levels, the pressure ratings of your kegs and fittings, and any alcohol content you declare. Use of this calculator is subject to our Terms and Conditions.

Plan recipes and track every batch with these calculators built in. Foambyte is free to start.

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How viability is estimated

Yeast cells slowly die while the package is stored. The calculator estimates the viable share from the days since manufacture:

\text{Viability} = e^{-0.004\,d}

where $d$ is the number of days since manufacture.

and the viable cells from the amount and the cell density of the yeast type:

N = a \times c \times \text{Viability}

where $N$ is the viable cells in billions, $a$ the amount (g or mL) and $c$ the billion cells per gram or milliliter of the yeast type.

For example, 100 mL of liquid yeast at 1 billion cells per milliliter, made 30 days ago, is about 88.7% viable and has about 89 billion viable cells.

To check whether that is enough for your batch, use the yeast pitch rate calculator. Inside Foambyte, yeast is part of each recipe and batch, together with the pitch rate and your fermentation readings.

Reference table

Estimated yeast viability by days since manufacture (rows), and viable cells left from 100 billion
Age	Viability (%)	Viable cells (billion)
0 days	100.0	100
7 days	97.2	97
14 days	94.6	95
30 days	88.7	89
45 days	83.5	84
60 days	78.7	79
90 days	69.8	70
120 days	61.9	62
180 days	48.7	49

Frequently asked questions

How is yeast viability estimated?

The calculator assumes the yeast loses viability at a steady rate of about 0.4% per day, or roughly 11% per month, so half of the cells are viable after about 173 days. It is the same estimate the Foambyte app uses.

Is the estimate the same for every type of yeast?

Yes. The calculator applies the same estimate to every yeast type. Storage temperature, handling and the strain have a large effect on real viability, so check the manufacturer's date and viability information, and treat the result as a guide.

How many cells are in my package?

The yeast types list typical cell densities, such as 1 billion cells per milliliter for liquid yeast. Manufacturers state the actual count for each product, so check the package and adjust the amount if needed.

What should I do if viability is low?

Pitch more yeast or make a yeast starter to grow more healthy cells. The yeast pitch rate calculator compares the viable cells you have with the cells your batch needs.