Co-purchase co-op with parents

Applying for a coop purchase and a mortgage are two separate processes. As for the mortgage write-off, I think it would depend on whose name is on the mortgage - you should check with your accountant. If it's your name but your parents are helping you out with the payments then I wouldn't think they would get the write-off.

If the parents are making the payments, then they'll most likely be on the mortgage since the child probably wouldn't have the assets to qualify by themselves. (Or else why even co-purchase?)

Thus, if they are on the mortgage, I think you can allocate the payments to whoever pays,
you just can't double dip? (Both parent and child cannot claim the deduction)
I don't know the details though.

(Or else why even co-purchase?)

Because typically coop financial requirements are much higher than lenders requirements.
You may need 50% down and 10X purchase price in liquid assets for example and the latter could come from the parents' side if the coop allowed it whereas the purchaser could qualify for a mortgage on their own so make payments on their own.

exis--that is correct. In this case the parents co-purchase are simply a way of qualifying for the co-op's net worth requirements, not to make the down payment or mortgage payments. My concerns were more in terms of the tax implications of my income tax mortgage deductions and capital gains when the apartment is sold.