Renovation Project Budget Builder
Renovation projects go over budget 80% of the time — the median overrun is 20-30% above initial estimate. The cause is almost always the same: underestimating scope, ignoring contingency, and overlooking soft costs (permits, design fees, temporary housing). This builder generates a complete line-item budget with realistic cost ranges for your project type and region, a calibrated contingency, and all the soft costs that contractors typically exclude from their bids.
total ÷ square footage
reserve for unknowns
on base construction
Construction core (base + markup) in dark; soft costs in grey; the contingency reserve in ember — the line people most often forget.
| Line item | Amount |
|---|---|
| Base construction | $50,000.00 |
| General-contractor markup | $9,000.00 |
| Permits & inspections | $1,500.00 |
| Design & architectural fees | $3,000.00 |
| Temporary housing | $0.00 |
| Other soft costs | $2,000.00 |
| Contingency reserve | $8,850.00 |
| Total | $74,350.00 |
View the TypeScript implementation on GitHub: packages/calc/src/renovation-project-budget.ts · view tests
What this means
The reason renovations blow past budget is almost never the part everyone obsesses over — the cabinets, the tile, the fixtures. It is the three categories nobody writes on the kitchen-table napkin: the contractor’s markup, the contingency for what demolition uncovers, and the soft costs that never appear in a bid. This builder forces all three into the open as their own line items, which is the entire point.
Notice where the contingency is applied. It sits on top of base construction plus the GC markup — not on the soft costs — because surprises surface in the work itself: the rot behind the wall, the knob-and-tube that has to be replaced, the framing that was never up to code. Those are the dollars you cannot see until a wall is open, and they scale with the size of the construction, not the size of your permit fee.
In my experience, the single most useful thing this builder does is show people the gap between a contractor’s bid and their actual cash outlay. I’ve found that a bid and a budget are not the same document: the bid is labor and materials and the GC’s cut, while the budget is everything that leaves your bank account. I’ve seen the band do the rest of the work — once someone sees a total expressed as a range instead of a single confident number, they stop treating the lowest bid as the real price and start keeping a reserve they can actually draw on mid-project.
Worked example
Take a 200 sq ft mid-range kitchen renovation at a base of $250/sq ft, hiring a general contractor at the typical 18% markup, with $1,500 in permits, $3,000 in design fees, no temporary housing, $2,000 in other soft costs, a 15% contingency, and a ±20%estimate band. Base construction is 200 × $250 = $50,000. The GC markup applies to that base only: $50,000 × 0.18 = $9,000. The contingency applies to base plus markup: ($50,000 + $9,000) × 0.15 = $8,850.
Add the soft costs that the contractor’s $50,000 bid never mentions — $1,500 permits, $3,000 design, $2,000 other — and the total comes to $74,350, or about $372/sq ft all-in. That is the number that matters: nearly 50% above the headline construction cost. The band puts a realistic planning range of $59,480 to $89,220around it, so when the lowest of three bids comes in at $50,000 flat, you already know it is missing roughly $24,000 of cost you will pay regardless — and you have the reserve to absorb what the demolition turns up.
Frequently asked questions
The information and tools on this website are for general educational purposes only and do not constitute financial, investment, legal, or tax advice. Consult a licensed professional for decisions specific to your situation.