I get this question frequently.
The first and truest answer is: I don't know.
That said, what I tell people is that it depends on several factors:
~what are your goals and priorities?
~what can you realistically afford?
~what kind of time can you devote to massage or bodywork?
~what kind of self-care are you doing, or willing to do, between sessions?
Often, what I will recommend to someone coming in with a complaint that they are eager to fix is: come in for weekly treatments for 3-4 weeks, and then let's re-evaluate. If money or scheduling is an issue, it might be bi-weekly for 3-4 treatments, or it may mean doing shorter, more focused treatments.
I know, from experience, that regular bodywork brings change; people get results. Clients are pain-free for longer periods of time between sessions; they regain range of motion; they report decreases in insomnia and more restful sleep; they are inspired to take better care of their bodies beyond bodywork.
If there is one thing I can encourage clients to do, it is this: go for bodywork before reaching a state of absolute misery. There is no point in "saving" a bodywork session for when you absolutely cannot stand the pain or tension anymore. Resist the temptation to fall into this trap.
Personally, I go no longer than 3 weeks without bodywork. When I can swing it with scheduling and/or finances, I go weekly; generally, it's every 2 weeks. I recognize the value of it to my well-being, so I prioritize it. If I didn't, I suspect I'd have no business being a bodyworker!
:)
