How much can you really afford to spend on a house?

If the last few years have taught us anything, it's this: Never buy more house than you can afford.

In many instances, that might be less than you've been led to believe, particularly by people whose commissions or fees are based on how much they can talk you into spending.

That's nothing against salespeople -- they're only doing their job. But you wouldn't ask a car salesman how much you should spend on a car (we hope!).

Before you even start house hunting, make sure you decide -- with no outside pressure -- the maximum amount you will spend on a house.

Too many people spend every dime and take out the biggest loan they can get to buy a house, and in no time start losing sleep wondering if they can make their mortgage payments.

Follow these 4 smart moves, however, and you'll have little or no trouble paying for your home.

Smart Move 1
Spend 30% or less of your gross (pretax) income on housing costs.

Add together monthly income -- before taxes and other deductions -- from your job, your spouse's job and part-time or side businesses if applicable.

Multiply that number by 30%. The result is the maximum total amount you should spend on monthly housing costs -- including principal and interest on the mortgage, property taxes, condo or association fees and insurance.

For years, the U.S. government has defined an affordable home as one that costs less than 30% of your pretax monthly income. Spending less is even better.

Liz Weston, author of The 10 Commandments of Money, recommends keeping your housing costs down to 25% or less of your income.

For example, if you make $60,000 a year and have no debts, you can afford to spend about $1,500 a month on principal, interest, taxes and insurance without breaking the 30% rule. To keep housing costs down to 25% of your income, as Weston recommends, you'll have to spend $1,250 or less.

Nearly 37% of homeowners with a mortgage -- 19 million people -- now spend more than 30% of their income on housing.

That's one crowd you don't want to follow.

Smart Move 2
Spend no more than 36% of your income on total monthly debt payments.

The more non-mortgage debt you have, the less you can afford to spend on a home.

Multiply your income from Smart Move 1 by 36%.

Plan to spend no more than that result on your total debt payments -- mortgage payments, auto loans, student loans, credit card bills, child support and loans against your 401(k) plan.

For example, if you make $60,000 a year but you spend $300 a month on car payments, $125 on credit card bills and $200 on student loans, the 36% rule would limit your monthly housing costs to $1,175.

It's easy to put these rules to work. Just enter your income and non-mortgage debt payments into our mortgage calculator, and we'll tell you how big of a loan and monthly payment you can afford.

Smart Move 3
Choose wisely if you must tap retirement accounts for a down payment.

Take the amount you can safely borrow for a home, add however much you've saved for a down payment and that's how much you can spend on a home.

Ideally, the money you use for a down payment should be savings you've specifically set aside for a home.

But if a lender demands more up-front cash than you expected, an Individual Retirement Account (IRA) or 401(k) may be the only place you can turn for another $10,000, $20,000 or more.

If that's the case, tap a Roth IRA or Roth 401(k) plan first.

Since contributions to Roth plans are fully taxed before they're made, you can withdraw however much you've put into those accounts at any time without incurring any penalties or additional taxes.

If you've held a Roth IRA for at least five years, you can withdraw an additional $10,000 in earnings without paying any penalties or taxes to buy or renovate a first home.

The next place you should turn is a traditional IRA, which will allow you to withdraw up to $10,000 for the purchase of a first home without penalty.

If you and your spouse each have a traditional IRA, then you can take $10,000 or a total of $20,000 from your two accounts penalty-free.

But since contributions to traditional retirement accounts such as this are tax-deductible, you'll have to pay income tax on withdrawals that exceed those limits.

Any withdrawals above the limits are subject to income tax and a 10% penalty until you reach 59½ years old.

Your employer's traditional 401(k) plan is the last place you should turn for a down payment.

It has no special provisions for down payments, and any "hardship withdrawals" are fully taxed and incur a 10% penalty until you turn 59½.

The better option is to take out a loan against your 401(k) account.

You can usually borrow up to $50,000 or half the value of the account, whichever is less, and take up to five years to pay it back.

The interest you're charged, which is generally a couple of percentage points above the prime rate, goes into your retirement account and the monthly payments are deducted from your paycheck.

But now you're talking about a new monthly expense that will reduce the amount you can afford to borrow for a home.

If this must be a part of your plan, go back to Smart Move 2 and recalculate.

Smart Move 4
Move in with a reasonable rainy day fund.

When anything goes wrong for people who live paycheck to paycheck, they have nowhere to turn.

A job loss, emergency home repair, disaster or health problem could easily keep you from being able to pay your mortgage. Record numbers of homeowners have lost their homes under such circumstances.

You can increase your financial security by keeping three- to six-months' income in an easily accessible savings account or other emergency fund.

You should also have enough cash on hand to cover home repairs, expected and unexpected. If you have to call a plumber on the weekend, for example, count on spending at least $200.

Weston recommends budgeting 1% to 3% of the cost of your home to annual repairs and maintenance.

You also need a larger emergency fund if you've chosen homeowners insurance with a higher-than-average deductible.

Although higher deductibles can lower your premiums, you must be prepared to cover more out-of-pocket expenses when disaster strikes.