A couple with two small children recently bought an 85-year old house in the suburbs outside of New York. Condo dwellers their whole lives, they were mystified when their lawn started turning brown.

They asked their neighbor if she had any idea what the problem could be.

“It’s been dry,” the neighbor noted. “Your grass needs water.”

The couple assumed that the gardeners they hired would also do the watering. And perhaps for enough money, they would.

Single family homeowners will tell you that no matter how new or old a house is, there’s always something going wrong with it. Whether you have to replace the roof, blacktop the driveway, or get your windows washed, maintaining a house can be expensive and time consuming.

But if you don’t keep up with the maintenance, the costs could grow exponentially. A house in less than perfect condition will sell more slowly and for less money than a house that’s been maintained impeccably.

Underestimating the true costs of owning and maintaining a house and the land on which it sits is one mistake first-time buyers often make.

Calculating these costs is a lot tougher than predicting your mortgage payments because they’re variable by nature and given to change. If PITIprincipal, interest, real estate taxes, and insurance–are the fixed costs involved with owning a home, utility payments are semi-fixed, and everything else fluctuates, sometimes with the season.

When you purchase your first home, you’ll be responsible for mortgage payments of principal and interest, paid monthly, or bi-monthly, if you have a loan that requires you to make payments every other week; real estate taxes, paid annually or in two installments, or paid monthly with the mortgage, if you escrow your insurance and taxes; homeowner’s insurance, paid monthly with the mortgage, if you escrow your insurance and taxes, but sometimes paid separately from the mortgage in an annual or semiannual premium; and, homeowner’s assessments or co-op monthly assessments.

Those are the big expenses that most first-time buyers expect. But don’t forget utility payments, including electricity, gas, cable, satellite, internet access, and perhaps Tivo; trash and garbage collection, including recycling as required by your local municipality; water and sewage; repairs and maintenance of the interior and exterior of the home (which includes everything from washing windows to replacing the roof, to painting the interior and exterior); landscaping and grounds maintenance (including driveway resurfacing, as needed, plus all the regular stuff); and snow removal (for those living in colder climates).

How do you plan for these costs? You’ll know how much your mortgage payment, homeowner’s insurance premium and taxes will be from the get-go. If your new house is about the same size as your old one, you can assume your utility bills will be similar. If the house is bigger, start multiplying.

But it’s the maintenance costs that are hard to estimate. A new roof can cost $3,000 or $30,000. If you have to put in a new sewage line, it can run $15,000. Fixing the washing machine can cost $100 for the visit or up to $1,300 to replace the machine if it’s unfixable.

The best way to be ready for the cost of owning and maintaining your home is to plan for it.

Depending on the size of your house, you’ll probably spend between $2,000 to $6,000 each year maintaining it. Some years, the total you spend will be less, perhaps because you don’t have any major expenses. And then in other years, when you have to repaint the interior or replace the carpet, you might spend more.

The easiest way to build your house maintenance fund is to set aside the cash each month when you get paid. Putting $200 each month into a special savings account means that when your house needs work, you’ll already have the cash on hand.