This calculator allows you to make a rough approximation of your monthly payment. Your monthly payment is comprised of the mortgage payment (principal and interest), which can be calculated exactly, plus one twelfth of the annual amounts due for property tax (which should be give a close estimate if you know the local tax rate) and insurance (which requires an actual quote). This calculator assumes that the value of the house itself is roughly half of the purchase price, and does not include earthquake insurance. Flood insurance is expensive, and not required in most areas. Disclosure documents for specific properties should indicate whether the property is in a flood zone.