Building a Realistic Construction Budget

A construction budget that only totals up quoted trade prices is missing the categories that most commonly cause overruns: a contingency line, soft costs, and an allowance for items not yet selected at the time of budgeting.

A contingency of roughly 10-20% of the hard construction cost is standard industry practice for renovations, where unknown existing conditions (behind walls, under floors, in older mechanical systems) are common. New construction on a clean site can often use a smaller contingency, but zero contingency on any project is a sign the budget has not accounted for realistic risk.

Soft costs are frequently underestimated or forgotten entirely: permit fees, design and engineering fees, geotechnical or environmental reports if required, temporary services (site power, portable sanitation), and financing costs (interest during construction if the project is loan-funded) all belong in the budget, not just the trade contracts.

Allowances deserve particular care. A budget line that says 'flooring allowance: $8/sqft' is only useful if the owner understands that figure is a placeholder, not a guarantee -- the real cost depends entirely on the material eventually selected. Tracking allowance items separately, and updating the budget the moment a selection is made (rather than waiting until the invoice arrives), prevents allowance overages from becoming a surprise at the end of the project.