How to Use a Home Addition Calculator

Table with a calculator, home model, pencil, and list of renovation costs
Photo: krisanapong detraphiphat / Getty Images

To understand what a home addition or renovation will cost, many homeowners will use a home addition calculator to help them determine if the changes are worthwhile. While these calculators can be extremely beneficial they also have some drawbacks.

A home addition calculator will be most useful to a person in the initial planning stages of construction or home improvement projects. It is not a tool that can help you to negotiate with a contractor because contractors don't use this sort of gadget.

Key Takeaways

  • A home addition calculator can help you decide whether it’s worthwhile to make renovations to your home. 
  • A home addition calculator doesn’t account for the cost of labor and materials in your particular area. 
  • You can also find out the cost of an addition by getting estimates from three to five contractors.

How Professionals Estimate Costs

When professional contractors estimate the costs of an addition, they don't rely on gimmicks. Instead, they arrive at their estimates by relying on facts, science, and their previous experience. And as for home addition calculators, they rely on algorithms and mathematical equations that are powered by technology.

For a homeowner without construction knowledge, a home addition calculator is a good place to start. But regardless of the estimate it produces, you will have to account for the costs of materials and labor within your local market and community, which could drive the estimation higher or lower.

The National Association of Realtors (NAR) local website lets you input your city and state into a search to find out the average cost per square foot to build a house. According to NAR calculations, Austin, Texas is $332 per square foot; Charlotte, North Carolina is $213 per square foot; Knoxville, Tennessee is $179 per square foot. San Francisco, California? A whopping $1,000, more than five times that of Knoxville.

The Purpose of a Home Addition Calculator

A home addition calculator is not a physical calculator you can buy at Amazon and receive delivery by drone. It is available only online at various websites, some for free and some require an account. You enter basic information and an estimate pops up. An assortment of variables is available to choose from such as:

  • Will you do the work yourself, hire a general contractor, or be your own general contractor, subcontracting work to others?
  • Which part of the home will you remodel or add onto with an addition? For example, a garage is much less expensive to build than a kitchen.
  • Are your materials inexpensive, average or upscale? For a bathroom, Calacatta marble is a luxury stone that can cost 10 times more than ordinary porcelain tiles.
  • What size is your project? Obviously, the larger the area, the higher the overall expense.
  • How much is your home worth now? While this amount has a definite bearing on the cost to improve, do not expect to necessarily see a 100% return on investment at resale. Remodeling Magazine shows year after year how rare it is to make a profit.

Obtaining a Permit

After you have determined an average cost by using a home addition calculator, consider obtaining a permit. Without debating whether permits are worth the additional cost, whether permits require other upgrades or whether your neighbors do work without a permit, consider the inherent problem on resale without a permit. Appraisers will most likely not include the upgrades or addition if there is no permit on file.

If you hire a general contractor, to save costs, the contractor might suggest you bypass the permit. Ask if the contractor will obtain a permit and insist on receiving a copy of the permit, including the completion certificate. Sellers of a home in Carmichael paid their contractor more than $100,000 to add a master suite.

They thought the contractor had obtained a permit. When we sold the house, the appraiser could not find a permit for the room addition, which resulted in a low appraisal. The sellers paid $8,000 to the county of Sacramento to obtain an as-built permit. Buyer's lenders today expect to see a permit.

Alternatives to a Home Addition Calculator

The best way to calculate a home addition is to do it yourself. Begin by determining the scope and size of your project. Then select your design and materials.

  • Measure the square footage and draw the scale on graph paper.
  • Determine the height, width, and depth of built-in items, allowing for window heights.
  • Assemble a catalog of all itemized materials with prices.
  • Present your package to a minimum of three to five contractors and obtain individual estimates.
  • Obtain a time estimate to complete the job from inception to finish.
  • Prepare for the unexpected and 10% to 15% cost overruns.

Tip: Make sure all of your materials are on site before the contractors show up for work.

At the time of writing, Elizabeth Weintraub, CalBRE #00697006, is a Broker-Associate at Lyon Real Estate in Sacramento, California.

Was this page helpful?
The Balance uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Realtor. "Find Your Ideal Neighborhood."

  2. HomeAdvisor. "How Much Do Marble Countertops Cost?"

  3. HomeAdvisor. "How Much Does It Cost to Install Ceramic or Porcelain Tile?"

Related Articles