Free tool

Project Simulator

Planning more than one project? Tick the boxes, set the scale, and we roll 10,000 Monte Carlo scenarios to show a realistic combined budget — the most-likely total plus a safer-budget figure — instead of just adding up the low and high estimates.

Built by a licensed structural engineer (P.E.) · Last reviewed June 22, 2026 · A planning simulation, not a quote or bid.

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Select one or more projects to roll the simulation.

Why a combined estimate isn't just low + low and high + high

Add up the low ends of five projects and you get a best case that almost never happens — every job would have to land at its cheapest at the same time. Add up the high ends and you get a worst case that's just as unlikely. The honest answer sits in between, and it's tighter than the naive sum: across many projects, some run high while others run low, so the combined total clusters toward the middle (the portfolio effect).

But the projects aren't fully independent, either. A hot regional labor market or a materials price spike pushes several of your projects up at once. Ignoring that correlation would understate your risk and give a false sense of confidence — so the simulator links the projects through a shared market factor. The result is a distribution: a most-likely total, and a safer-budget (P90) figure you have about a 9-in-10 chance of coming in under.

Method & sources

Each project's installed-cost band comes straight from its ProjectCostPro calculator (the same low-to-high range you'd see on that calculator's page, at a small / typical / large scale you choose). Per trial, each project's cost is sampled from a triangular distribution over its band with the mode skewed slightly high (cost overruns skew that way), and all projects are correlated through one shared market factor (implied correlation ≈ 0.5). We run 10,000 trials and read the percentiles off the results.

Real-world surprises (optional) add a right tail: for applicable projects, known but uncertain extras (rotted framing found during a remodel, a failed inspection, rock during excavation) are sampled with an approximate probability and a sourced cost range. Surprise odds are reasoned planning estimates; the cost ranges are sourced.

This is an AACE Class 5 (rough, early-planning) view made probabilistic — inherently wide, and a specific project can land outside the range. It states the probability of a cost; it is not a quote, bid, or guarantee, and it doesn't replace your contractor, permit, or inspector. Method follows standard construction cost-risk practice (AACE 41R-08 range estimating; GAO and NASA cost-estimating guidance on correlation and the portfolio effect). See the full methodology and data sources.

Estimates are planning ranges, not contractor quotes. The combined simulation states the probability of a cost, not a promised price. See how we build the ranges and the data sources. We don't replace your contractor, permit, or inspector.