I had a discussion with my son just a few months ago about this very subject. He wanted to set up a Patreon sort of thing where’d he would DM, so I sat down with him and we worked out what he’d have to charge and do to make a living at it, and at what level he’d be comfortable with.
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Assuming a 40-hour work week, 4 or 6 hour game session, plus prep time.
Desired: $15 per hour pay ($600 per week; $31.2K pretax).
Assuming Needed: 6 players per session. 2 sessions per day, 5 days a week - 60 players needed (that’s a lot of people right there).
Cost per player - $10 per session.
Not bad, but would you pay $10 per game session?
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This was a very basic napkin math, not including costs for materials (books, minis, computer, VTT, subscriptions, etc.), travel, medical, taxes, prep time (factor in prep time of 1-2 hours per group, you lose a day’s worth of players and cost per player rises about $2 per player). Likewise, a smaller play group would increase the cost too.
It’s definately one of those things that‘d be great if you can do it, but you’d certainly have to build up a client base - and it’d be a LOT of work to keep up with (10 game sessions worth of notes a week?).