There are a number of options/equity calculators:

https://tldroptions.io/ ("~65% of companies will never exit", "~15% of companies will have low exits*", "~20% of companies will make you money")

https://comp.data.frontapp.com/ "Compensation and Equity Calculator"

http://optionsworth.com/ "What are my options worth?"

http://foundrs.com/ "Co-Founder Equity Calculator"