About ADU Project Estimator

Clear numbers for a big decision.

Adding an accessory dwelling unit is one of the largest projects a homeowner can take on. The first questions are always the same: What will it cost? How would I pay for it? What could it rent for? Most answers online are a single national average, or a builder's sales page. ADU Project Estimator gives you a starting point based on your own project.

Tell a calculator what kind of ADU you have in mind, how big it is and where you live. It will show you an estimated cost range, what the monthly payments could look like, and how long rental income would take to pay back the build.

What makes our calculators different

• Built around your location. Building costs, permit fees and rents vary widely from state to state and city to city.
• The whole decision in one place. Cost, financing, rental income and payback, side by side.
• Built for your phone or computer. Use them at home or while you walk your property.
• Free, with no sign-up. Just open a calculator and use it.

How we calculate

Our calculators use published construction cost ranges, permit fee schedules and standard loan formulas. Each calculator page explains its math and its sources so you can check it yourself.

Results are estimates for planning. Your actual cost depends on your lot, your design, your builder and your local rules, so always get quotes from licensed builders and check with your local building department before you commit.

Who we are

ADU Project Estimator is built and run by Cool Apps LLC, a small independent software studio. We keep the site free by showing ads.

Have a suggestion for a new calculator, or found something that looks off? Please contact us.