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Houses, cars and vacations are three big-ticket items that almost all of us want at some point, but when can we afford them? To help you decide just how much you can afford, we spoke to seven experts about how to make these decisions, and about the most common mistakes that get people into trouble. Here's your guide to deciding what you can afford -- and what you can't.

Can I afford a house?

Factors to consider: Whether you're ready to make a sizable down payment (15% or 20%), how long you plan to stay and if you can handle additional expenses such as maintenance costs -- as well as swings in the real estate market -- all play a role in whether it's a good time to buy.

The hidden costs: "The purchase price of a home is only a wee part of the real cost of buying a home," says Carmen Wong Ulrich, the author of "The Real Cost of Living: Making the Best Choices for You, Your Life, and Your Money." Aside from closing costs, insurance and fees, buyers also take on the risk of the housing market. If the value of your home goes down, the value of your assets falls. That's why Ulrich says you should also consider the stability of your job, the neighborhood, schools and the overall state of the housing market in the area before you take the plunge.

Elisabeth Leamy, "Good Morning America's" consumer correspondent and the author of "Save Big: Cut Your Top 5 Costs and Save Thousands," recommends that renters buy a house only if the mortgage payment will be similar to their rent payment. "If you can afford your rent payments, you will be able to afford your house payments. It's that simple," she says.

For some people, though, even that amount can be too high, says Farnoosh Torabi, the author of "Psych Yourself Rich: Get the Mindset and Discipline You Need to Build Your Financial Life." "You need to remember that owning a home involves some extra expenses, namely taxes, common charges and upkeep. If a pipe breaks loose, there's no super or landlord to cover the cost. It's all coming out of your pocket."

Common mistakes:

  1. Moving within a few years. Buying a house generates a lot of transaction costs. Financial expert Manisha Thakor estimates that they can add up to about 10% of the total purchase price. That means you want to live in the house long enough for price appreciation to offset those costs, she says. One rule of thumb is to plan on settling in for at least five years.
  2. Borrowing the maximum amount allowed by the bank. It's tempting to take banks up on their pre-approved offers, but those offers don't always factor in potential changes in your income. If you start a family and one spouse decides to stay home, for example, your household income could be cut in half. "You want to factor that in before you buy," says Thakor.
  3. Forgetting to look beyond the numbers. "You might be able to financially afford to buy a home, but is it worth it to you? If you enjoy a transient lifestyle, then it might not be," says Torabi.

Laura Vanderkam, the author of "168 Hours: You Have More Time Than You Think," adds that the less you spend on your house, the more you'll have for other enjoyable activities, such as trips, dinners out and entertainment. "Those things might actually make you happier than a more expensive house," she says.

Can I afford a car?

Factors to consider: Your lifestyle, maintenance costs and personal tastes all play a role in deciding whether it makes sense to buy a car.

The hidden costs: Depreciation means that the moment you drive your new purchase off the lot, its value plummets. That's why Ulrich asks why anyone would bother buying a new car. "Imagine what else you could do with those thousands of dollars," she says. Instead, she recommends buying certified pre-owned vehicles.