Depends on what calculator you used. Some of them do allow you to put in estimated taxes and such, and in that case, a result stating just the P&I is probably just that - just your principal and interest.
Most of the basic calculators (e.g. put in how much you make, put in how much your monthly debt payments are, and out pops a result) the result is you maximum PITI that is likely to be approved, and that maximum would be including tax and homeowners insurance.
You can probably figure it out pretty easily though, most of those calculators are based around a 28-31% ratio for your PITI to your gross, and a 39-41 or so max ratio for your PITI+other monthly debts to your gross.
So, to ballpark it yourself, do the following:
Multiply gross monthly income by 0.30 (e.g. if you make 5000 before taxes each month, that's 1500 max that a bank is likely to allow for principal, interest, taxes, and insurance).
then Multiply gross monthly income by 0.41, and subtract monthly debts (e.g. using the above 5000, if you have a $250 car payment and a $50 visa payment each month, it works out to $1700 that the bank would consider a safe amount for your total debts per month).
Then take the smaller of the two (in the example above, even though the bank would consider you to be safe taking on $1700 additional debt per month, they would only loan you enough to add on another $1500 a month, because that's the max they consider safe for the front end (housing) DTI).
The ratio's will change a bit, and even last year they would have been SUBSTANTIALLY higher, but right now the mortgage industries are reeling from having been very badly burned over the past few years with their looser lending standards, so they're pretty much all reverting back to the older, more conservative, and less likely to default standards, and those are pretty much the 0.28-0.33 front end ratio, and around a 0.38 to 0.42 back end ratio, and those are the ones the calculators are based around.
Of course, if you do have sterling credit and a good down payment, I understand you can get larger ratios, one of the pro mortgage folks around here might be able to tell you more about them if you'll give some more information on your particular situation.
