My bank has a great calculator for estimating the PI payment along with taxes and insurance combined. But when you are looking to buy it is a good idea to take a good look into both your liabilities (such as the car payment and insurance) and also into your current spending habits.
A good book to take a look at (I borrowed a copy from the local Library) is Home buying for Dummies there is an entire chapter devoted to determining how much home you can truly afford. Versus the amount you may be approved for there are many things the bank does not take into consideration.
Here are a few of them for an Idea (but I reccomend reading some basic home buying books because im sure I will forget something)
Basic Home expenses:
1) Principle and Interest payment
2) PMI if you do not have a 20% downpayment (unless you qualify for a VA loan.)
3) Home insurance
4) Liability Insurance
5) Home Maintence and Repairs
6) HOA dues
7) Utilities -water sewer waste cable phone electric
8) Property Taxes to include any other special assements
Other Monthly Liabilities to consider:
2) Transportation costs - maintenance, Fuel, state registration fees, Tolls or parking fees (if applicable)
3) Debt Repayment - Auto Loan, Student Loans, credit card debt or anything else that requires a monthly payment
4) Health care - Insurance, dental and vision,
5) Insurance - auto, life, disability
6) Clothing, shoes, haircuts, dry cleaning, makeup, other
7) Child care, toys, clothing, school...
8) Retirement savings
After looking through your monthly expenses determine what amount is left over monthly. That should give you an idea of the amount you can really afford for a home. The monthly amount you can afford should take all the basic home ownership expenses into account.
My husband and I have been looking into buying a home and while the bank could approve us for nearly 200k we found we were more comfortable with closer to 100k once we reviewed our spending habits and monthly obligations.
Just remember the bank is never telling you what you can AFFORD when they approve or qualify someone they are only letting you know the maximum amount that they will let you borrow.
Also take into consideration closing costs when buying some mortgage brokers will offer a loan with little or no closing costs but they may end up costing an arm and a leg later on in the form of higher interest rates and fees.
Personal Home Buying experience Along with :
Home Buying for Dummies
Suze Ormans 2009 action plan
Buying a House on a shoestring
Investing in Fixer Uppers