What monthly costs should I calculate before buying property?

An end-user may also need to add utilities, lender-required insurance where applicable, and move-in or furnishing expenses if relevant.
An investor should think in terms of net cash flow, not gross rent: how much remains after service charges, management, and likely vacancy periods? Some properties look attractive at the point of purchase but become uncomfortable after handover because the owner never modeled the real monthly carrying cost.
Build the decision around expected net monthly burden, not around the initial sticker price alone.