If your home only has one bathroom, you can recoup a large chunk of your investment by adding another one. Estimates show that you can recoup between 80% and 130% of whatever you spend adding a bathroom.
When it comes to finding room in your house for an extra bathroom, take a look at any extra rooms or underutilized spaces. Consider other spaces, such as closets or areas under the stairs, too. If you want a half-bath you need at least 1.7 square meters. If you want a full bath, including a stand-up shower, you need at least 2.8 square meters. If you want a bathtub, make sure you have at least 2.3 square meters to work with for a bathroom addition.
Like any project, the cost of adding a bathroom depends largely on the types of additions and accessories you want to use, and the cost of each of these items.