Membership
Monthly massage and spa memberships are priced so that they are excellent value if you go, and quietly expensive if you do not. The whole answer turns on one honest number, so this puts that number on a slider and shows you what it does.
1 visit a month. Be honest rather than aspirational. This single number decides the answer, and it is the number the whole membership model is built on people getting wrong.
Most contracts run 12 months before you can cancel freely.
Tips are almost never included in a membership.
They usually do, and they usually expire a set number of days after you cancel. A rolled-over credit is only worth something if you will actually use it.
over 12 months at 1 visits a month
A membership fee buys a credit each month, credits usually roll over, and members pay a reduced rate on anything extra. The business is priced on the gap between intended and actual visits: at one visit a month it is normally a genuine discount, and at one visit a quarter it is a subscription to a promise. Both of those are in the same contract.
Some people go more often precisely because they have paid already, and for a genuinely useful habit that commitment device can be worth money on its own. That is a real effect and it does not show up in this calculator. What the calculator can do is make sure you are buying it deliberately rather than by accident.