Build Cost Calculator
Estimate total construction cost from floor area and a rate per square foot, then add contingency, professional fees and tax to get a real budget.
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A builder's rate per square foot is the start of a budget, not the budget. Contingency, professional fees and tax routinely add thirty percent or more, and projects that run out of money almost always did so because those three lines were treated as optional.
The rate itself varies enormously by location, specification and building type, so it has to come from local quotes or a published cost index for your area rather than from a national average.
How it is built up
Base cost = area × rate. Contingency is applied to the base, professional fees to that subtotal, and tax to the whole. Applying each in sequence rather than adding all the percentages together is what produces the correct figure.
Worked example
Two thousand square feet at 200 gives a base of 400,000. A 10% contingency takes it to 440,000, 12% professional fees to 492,800, and 5% tax to 517,440 — an all-in cost of about 259 per square foot against a headline rate of 200.
Contingency is not padding
Ten percent is a minimum on new build and twenty or more is realistic on renovation or anything involving an older structure. Opening up a building reveals problems that were not in the quote, and a project without contingency stops at exactly that moment.
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Create your free property pageFrequently asked questions
What rate per square foot should I use?
One from local quotes or a published regional cost index, not a national average. Rates vary by a factor of three or more between locations and specifications, so an imported figure will be badly wrong.
What do professional fees cover?
Architect, structural engineer, services engineer, quantity surveyor, planning consultant and project management. Ten to fifteen percent of construction cost is typical, and complex or heavily serviced buildings sit at the higher end.
Does this include the land or the finance?
No. This is construction cost only. Land, finance during the build, sale costs and developer profit sit outside it — use a residual land value calculation to bring all of them together.
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