I'm about to introduce a partner to my business to help me out with most of my daily tasks including project management, support, taking sales calls and so on.

Now the question is, how do I pay them? I can only afford to pay them a percentage of profits but how do I work out what to pay them? How do I make sure I'm not over- or under-paying them their dues? What calculation method do we agree on before we start?

How is this normally done?

Thanks!