Construction Cost Calculator: Friend or Foe?

We live in a time where consumers are turning to the internet first when they are searching for information. And when it comes to home renovations and custom home construction costs, it’s no exception.  The cost of custom home construction and home renovation is a popular internet search term, and many websites claim they can provide an online estimate.

But how accurate are these building construction cost calculators?  We’ve taken a look at a few popular projects to find out how accurate these calculators may be.

Custom Homes

We priced a 2,500 square foot, two storey home with above average finishes, two car garage and an unfinished basement on a country lot outside the city.  The cost came in at $170 SF, excluding cost of utility hookups, design and permits.  A reasonably accurate figure, based on our experience.

New construction is easier to estimate than house addition and renovations, therefore it is possible to build a building cost calculator that provides some level of accuracy.  The cost of building a new home depends primarily on design, level of finish, location (urban or rural), and site conditions.  A cost calculator that can factor in as many of these variables can be built to be fairly accurate.

House Additions

We looked at a website with a house addition cost calculator.  A 300 square foot addition would cost $30,000 or $100 per square foot.  No word on if this includes design, permits, and taxes.  Regardless, the figure was unrealistically low for any house addition, especially an urban area such as Toronto.

Adding a bathroom to the addition would increase the cost by $900. Seriously!  We couldn’t find a licensed plumber to do the plumbing work for that price. Not to mention everything else that goes into building a bathroom.

Every house addition is unique.  It is designed to fit with the existing home, and meet the needs of the homeowner.  Experienced builders spend hours preparing an estimate for a house addition.  Expecting an online building cost calculator to produce an accurate figure is foolish.


We priced standard renovation to a 5’x8′ bathroom, and it came in at $18,000.  That is a high number for a standard bathroom renovation, from our experience.

Renovation and remodeling, like the house addition construction we just discussed, is custom work.  Every renovation has its unique requirements, based on existing house conditions and the wants and needs of the homeowner.  This makes them more difficult to price.  It takes minutes to punch in a few numbers into an online construction cost calculator, while the professional renovator will take an hour to consider all aspects of the work and price it properly.

What’s the big problem with building cost calculators?

The big problem with building and construction cost estimators (besides the fact that they are wrong most of the time, in our experience) is that that homeowners are using them to make decisions on whether or not to build or renovate.

In some cases, the cost looks attractive and the homeowner decides to go ahead with creating plans and getting a building permit, and then cannot find a builder who can complete the project within the budget they have.  In other cases, the cost may look too high and the homeowner decides not to do the work, when in fact the actual cost would have been affordable.

Use the internet to look for renovation ideas and products for your home.  Use the internet to find a reputable renovator or a builder.  But when it comes time to get an estimate for the project, talk to a contractor or builder, have them look at the project, and provide you with pricing.