Estimating interior home improvement costs is a tricky business, and the best way for you to know that you are getting a good deal is to seek out several estimates. This estimator tool is a great resource to get you in the ball park, but it cannot come as close to the actual costs as a contractor can provide. Doors, plumbing, and flooring costs can have a great variance from company to company, which is why it is smart business to gather several estimates to better zero in on how all of these different components add to the cost of the project.