Not exact science and so so so many variables based on many things.

Here is one approach that might help you get to a framework to adjust from. Remember since you are a pre-existing company, it is really about share of value creation in the GROWTH of the company not the whole company.. that is CURRENT VALUE is the starting basis and so the question is how will the new partner help deliver the value above that current basis and how should that be shared?

- start w a value for the current pre-existing business. this value can certainly include value for where its is heading as is

- next, how would the two of you split things up based on expertise, experience, etc if you started a NEW company today... would it be 50/50? or do one of you bring more to the table than the other

- use that as one variable as a starting point of equity split of future added value.

- then look at other variables to add in or subtract out.. the company is not risky so the other partner is joining w less risk in the future, how is the new person being compensated vs you, is someone adding in capital or someone taking future capital risks, will you both be in full time, how stable is the company, etc..

- then you can also prescribe part as 'to be earned' (vested) based on certain targets for the partner or for the company...some of this is obvious '20% of your equity will vest based on you delivering Y.." but some is less so "I know the company, without you or someone else, would be worth X more in the next years, so I'll share a small part of that, but share a larger part of any value above that"

The idea is:
- current company value
- how do you see value split for new partner in creating new value to Company
- how risky is it / and who is bearing risks now and into the future
- criteria to vest "earn' part of it

hope that helps you some..

..... schwartz out