If you pay actors, you're not amateur.

Good afternoon.
The definition of 'professional' varies from licensing house to licensing house. Most, however, consider you 'professional' if you are paying your actors a living wage, regardless of equity affiliation. For instance, MTI considers you professional if 50% or more of your actors are paid $200 or more per week. Dramatic Publishing is only if ALL the actors are paid at least $150 per week.
Generally, Theatre's that pay stipends, even 'professional' ones, get treated as amateurs.

And to clear it up, professional theatre's ARE NOT charged more in royalties. If anything, they are charged potential less than their amateur counterparts. This is because while Amateurs are charged royalties payable 100% in advance that is equal to 100% of their potential ticket sales. This means that if you have a house that seats 500 people, and you make 500 seats available with a ticket price of $15, your royalty per performance will average $600-$900 for amateurs, depending on the show (shows average 10%-14% GBOR).

On the other hand, professionals only pay 50% of their estimated potential box office upfront. So, in this case, taking into account the same house and prices as above, the professional theater only pays $300-$450 per performance, and remits the remaining royalty at the same royalty rate as amateurs after the performance.

the advantage to this is that: amateurs will always be charged based on the maximum box office they could make, even though many don't meet this goal. Professional's only remit 50% of their potential box office, and only pay the remaining 50% on the ACTUAL ticket sales.

But in general, both Amateurs and Professionals are charged the same royalty percentage rates, which vary from 9% for a non-Broadway musical to 14% for something like Miss Saigon.

Same thing applies for straight plays, except that amateurs are usually only charged a small royalty ($75 per performance), were professional remit between 6% and 12% of their box office. In this case, amateurs could potentially get a better deal on royalties, depending on your actual ticket sales.

Thanks!