Firstly, assuming that your revenue exceeds your costs and that your business is in fact healthy, why would you want to bring in a co-founder and not an employe

Firstly, assuming that your revenue exceeds your costs and that your business is in fact healthy, why would you want to bring in a co-founder and not an employee, if you have managed fine so far? I would say it's likely to be a mistake. Especially if you have employees, since you would be bypassing them for promotion and bringing in someone from outside, sending a signal that you're not committed to employees working their way up through the business (see Jim Collin's books for more on this). Rather hire a great employee and train them up and promote them. Secondly, your question takes it for granted that you should "give" the equity away. Why? Surely, your prospective co-founder should buy his share if you both value your equity? If it's not bought it's not worth anything. You can't give it away, and certainly not for something promised which may never materialize. A bird in the hand is worth two in the bush.