The cost side comes from Renology published service and city guides, the same data behind the Renology Renovation Cost Index. The value side comes from the Zonda Cost vs. Value 2026 report, which publishes the percentage of a project’s cost a homeowner typically recoups at resale.
Estimated value added is simply the local cost range multiplied by the cited recoup percentage. Where the Cost vs. Value report has no figure for a project type, the calculator shows the cost range only and never estimates a return. Accessory dwelling units entered the report for the first time in 2026 with returns that vary widely by market, so they show a sourced note rather than a single percentage.
Recoup percentages are national averages. The 2026 report ranks the Pacific region, which covers California and Washington, first in the country, so returns for Renology metros run at or above the figures shown. All numbers are planning benchmarks, not bids or guarantees. Reviewed by Dror Gigi, Co-Founder of Renology.