If you're like many first-time homebuyers, chances are you've been spending your weekends driving around visiting open houses and new model homes. This is a great way to get a feel for what you want. The problem is that what you want isn't always what you should get.

Before you start touring homes for sale, it's important to start off with a budget so you know how much you can afford to spend. Knowing what mortgage payment you can handle will also help you narrow the field so you don't waste precious time touring homes that are out of your reach.

Where to begin
The key factor in figuring how much home you can afford is your debt-to-income ratio. This is the figure lenders use to determine how much mortgage debt you can handle, and thus the maximum loan amount you will be offered. The ratio is based on how much personal debt you are carrying in relation to how much you earn, and it's expressed as a percentage.

The ideal ratio
Mortgage lenders generally use a ratio of 36 percent as the guideline for how high your debt-to-income ratio should be. A ratio above 36 percent is seen as risky, and the lender will likely either deny the loan or charge a higher interest rate. Another good guideline is that no more than 28 percent of your gross monthly income goes to housing expenses.

Doing the math

First, figure out how much total debt you (and your spouse, if applicable) can carry with a 36 percent ratio. To do this, multiply your monthly gross income (your total income before taxes and other expenses such as health care) by .36. For example, if your gross income is $6,500:

Exceptions to the 36 percent rule

In regions with higher home prices, it may be hard to stay within the 36 percent guideline. There are lenders that allow a debt-to-income ratio as high as 45 percent. In addition, some mortgage programs, such as Federal Housing Authority mortgages and Veterans Administration mortgages, allow a ratio higher than 36 percent. But keep in mind that a higher ratio may increase your interest rate, so you may be better off in the long run with a less expensive home. It's also important to try to pay down as much debt as possible before you begin looking for a mortgage, as that can help lower your debt-to-income ratio.

Not only do you have to understand what type of mortgage you should choose, you have to understand the costs associated with your mortgage. All of these costs will be paid upon closing your mortgage.

Purchase Points
Purchase points, also known as a "buy-down" or "discount points," are an up-front fee paid to the lender at closing to buy-down or lower your interest rate over the life of the loan. Each point is equal to one percent of your total loan amount. If you have a $100,000 loan, one point would equal $1,000. The more points you buy, the lower your interest rate, but the more money you'll need at closing.

How do you decide whether you should buy points and if so, how many? Well, the decision should be based on how long you plan on living in your home and what you can afford to pay each month toward your mortgage. If you plan on living in your home for more than five years, it's probably a good idea to purchase points. The longer you live in your home, the more you can save on interest over the life of the loan.

Interest Rate
When you get a mortgage, you are charged an interest rate. This is the rate which the lender charges you for using their money to buy a home. It determines how much your monthly payments will be. Generally speaking, the higher the interest rate, the higher your monthly payment.

Mortgage interest rates change constantly. Daily, even hourly. If you speak to a lender and are quoted a specific interest rate, that's not to say you'll necessarily get that rate when you close on your loan. Not unless you formally lock-in that rate with the lender. Locking in an interest rate will guarantee you get your loan with a particular interest rate. Lenders will allow you to lock in for 15, 45 or 60 days. But the longer you lock in, the more expensive it will be, since it's more of a risk to lenders.

b>Fees
There are always fees associated with getting a mortgage, these fees cover the cost of processing and underwriting the loan. These fees can include charges for ensuring the title to the home is free and clear; paying for a land survey; or paying for a home appraisal which gives you the estimated value of the property (lenders require an appraisal to close on your mortgage).

Deciding which mortgage to get may depend on what each lender does because different lenders may charge different amounts. Some may charge lesser closing fees to lure you in, but may charge you a higher interest rate, which means you may pay more in the long run. But everyone has different needs.you may or may not be able to afford to pay more at closing and are willing to pay more over the long term.

Before it comes time to close, do your homework, make sure there are no hidden fees, and ask your lender lots of questions so that you understand all the costs involved with your mortgage.