It sounds like you've accomplished some things so far that de-risk the business, e.g. there is a working product and well-researched business plan (rather than

It sounds like you've accomplished some things so far that de-risk the business, e.g. there is a working product and well-researched business plan (rather than just an idea). However, it sounds like it would still be considered very early/risky -- no revenue, no customers, no significant funding, and no pay. I suggest doing many of the online equity calculators just to get a few different perspectives. However, assuming he is being paid entirely in equity, 85/15 might be low. (This assumes someone who will go all-in alongside you, will contribute an equally substantial amount long-term, and that there is no "revenue split" -- not sure how that works exactly.) One perspective you can take is based on assumed valuations. For example, say the company supposes an initial preferred stock valuation of $4M. Then, common stock might be valued at 30% of this -- $1.2M. You proposed the new co-founder might vest 15%/4 = 3.75%/year -- which would only be valued at $45K/year. Plus they have to deal with the one-year cliff risk of getting nothing, making it extremely risky for them overall. Hence, assuming all of the above, an 85/15 split may be low. (In support of this is considering what % you'd have to give up to raise money for the work you've already accomplished, as another commenter noted.) Also consider that this is at the very beginning of the company and you may want to look moreso forward -- would their presence greatly increase the company's chance of success? Whatever you decide, the key is to be completely honest and upfront with your potential co-founder so that you both completely understand the agreement and are satisfied with it!