If you’re thinking about adding a swimming pool to your backyard, then chances are the cost of the project is a top concern.

Asking a local pool company how much a project will cost, however, is like asking how much a house costs to build. There’s no one size-fits-all answer.

Poolpricer.com gives a rough estimate of between $25,000 to $50,000 for an in-ground pool. It also doesn’t factor in the cost of your pool’s upkeep.

“I’ve seen examples of homeowners getting hit with such costs after the start of the project by their pool company many, many times,” says Marcus Sheridan, with River Pools and Spas in Warsaw, Virginia.

Sheridan says that an occasional hidden cost is inevitable, and that “most can and should be caught, or at least brought to light, beforehand.”

Here are six hidden costs that River Pools and Spas says can derail even the best-planned pool installation budget.

• Dirt hauling: When an in-ground swimming pool is built, a significant amount of dirt comes out of the ground and has to go somewhere.

• Lawn and landscaping: The process of putting in an in-ground swimming pool requires a lot of heavy equipment. That’s bad news for your manicured lawn. Any grass in this area, and perhaps on the path to the pool location, will need to be seeded or replaced after a pool installation.

• Extra concrete: Homeowners often forget they will need patio space around the pool, which usually means more concrete.

• Electrical: Some pool builders include electrical hookup in their standard package, whereas others treat it as a separate invoice.

• Fencing: Almost every city requires a pool be behind a fence of some form.

• Retaining walls: These structures can be pricey. They also have extreme importance in terms of pool and deck stability, as well as proper yard drainage.