Whether you’re planning to sell or you want to stay in your home for the long run, chances are, at some point, you’re going to want to do a home renovation. Part of a successful home renovation project is, of course, making the changes you want to your home. But another part is staying within your budget–and, according to a recent study, that’s the part that many homeowners struggle with.

A recent study from Discover Personal Loans found that many homeowners seriously underestimated the cost of home renovation projects—sometimes by thousands of dollars. For example, the homeowners perceived the cost of a kitchen remodel to be $10,388. The actual cost? $19,920—a difference of $9,532 (or a whopping 48 percent). Homeowners similarly underestimated other home renovation projects, including deck construction (35 percent), bathroom remodels (31 percent), and AC installation (42 percent).

What does this mean for you? If you’re thinking about renovating your home, make sure you get an accurate estimate before you start renovations. And, if you’re planning to sell, make sure those renovation costs will add value to your home—and help you fetch a higher selling price when you put your home on the market.