Rent v. Buy Calculator question

Yes, for co-ops maintenance includes both taxes and what would be "common charges." Condos list out taxes and common charges separately. However the percentage of maintenance that goes to property taxes versus upkeep varies for each co-op. The listing agent for whatever co-op you are looking at should be able to tell you what percentage of the maintenance goes to taxes and what goes to upkeep.

As CCL3 states, you have to take co-ops on a case by case basis. The tax portion of the maintenance can vary between 30% and 75%.
Your 50% formula on every co-op wont work.

I agree about using 50/50 for this reason: IMO, the point of this type of calculator is to teach how much change in price impacts the equation. If you tweak all of the parameters it makes little to moderate change in rent vs buy, but if you change the appreciation rate it blows out the other fine details. So the calculator leaves you pretty much where you started: how do you think the housing market will appreciate within the number of years you plan to own?

Also the calculator illustrates this peculiarity of amortization: On a 20% down/30 y mortgage, it takes ~4 years of principal amortization as part of your monthly payment to build up 6% equity which is the commission you pay sell the apartment, if price stays constant. So that is roughly the floor for owning although many people will say you should plan to own for longer as an investment.

^^^yes, also you should own for longer to break even on what you have paid in closing costs for the purchase (tens of thousands of dollars).