# Yeast Calculator ![Calculate how many yeast packages to add or how big of a starter to make](/files/-LFRz7vV7GrzRxnwYWEd) ### PurePitch Formula for calculating viability for White Labs PurePitch® yeast packets is based on official data found here: Average viability of PurePitch® pure liquid yeast over a period of six months: | Time | Viability | | -------- | --------- | | 1 month | 99.21% | | 2 month | 98.05% | | 3 month | 90.26% | | 4 months | 84.28% | | 5 months | 79.35% | | 6 months | 71.59% | --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.brewfather.app/br/tools/yeast-calculator.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.