Market for a pre-Series A non-founder CMO making market salary is something in the 5–10% range. Post-dilution through Series C, that’ll take you down to about a point, fully de-risked.
But we’re not offering market salary are we?
Giving up $Xk per year in cash, over five or so years (early stage CMO isn’t likely your late stage CMO) = X*5 in present value equity given the fact that we’re still not accounting for risk AND the additional time it will take before the company is likely to deliver any return (another 5–10 years).
What does that look like in points? No idea, as it depends on present valuation, investment requirements and plans, post money valuations, etc. but easily fair to say 15%+