Principal and interest are the part everyone quotes. This adds the property tax that gets reassessed upward every year, the maintenance nobody budgets for, and the investment return your deposit gave up by sitting in a house.
Usually far more than principal and interest. On a typical 30-year loan, property tax, maintenance and the forgone return on your deposit can add close to half again on top of what the loan statement shows.
A common rule of thumb is 1% to 2% of the property's value every year. This calculator lets you toggle that buffer on and grows it in line with the property's value.
It depends partly on what your deposit would have earned elsewhere. Switch on the opportunity-cost option to add the investment growth you give up by putting that money into a property instead.