Depending on the region of the country, including an in-ground spa might add around 15 to 25 percent of the cost of the basic pool.

Factors that typically affect the bottom line include: spa size, spa shape, and spa-pool configuration. Common design variables include the spa’s position—is it built within the pool perimeter (an “interior spa”) or outside the perimeter (an “exterior spa”), the spa’s elevation—is it level with the pool surface or raised above it, and decorative finishes or special features such as custom dam walls and spillways.

The cost may also be affected by the excavation work needed to level the ground where the spa will go. Including a spa may also require the purchase of a more powerful pool heater to quickly warm the water or a bigger pump to power the hydrotherapy jets. However, these additions maximize a spa’s benefits and extend the months each year you can enjoy them.