Type your Whatcom County address. We pull the lot and zoning from public county maps, place ADUs on a site plan, and then walk you step by step through selling or renting the finished units. ADU rules are built in for the City of Bellingham only; other cities need their rules checked by hand.
📍 Now live for Whatcom County, Washington only. Other counties are coming.
Automate your ADUs on any site
Type a Whatcom County address. In a few minutes ADU Math pulls the parcel and zoning, draws a site plan with 1 to 3 ADUs that fit the setbacks, and builds a full ROI to sell or rent. Every number is editable, there's a sensitivity page, and the whole thing prints to a clean PDF.
Lot lines, size, zoning, and assessed value come straight from Whatcom County's public GIS.
A site plan that checks itself
Drag the house and ADUs. Setbacks and separations are checked live, with pass or fail in plain words.
Sell or rent, side by side
A 12-month sell case, a rent-and-hold case with IRR, and a build cost × house value sensitivity grid.
Whatcom County, WA only for now. Bellingham's ADU rules are built in. Other Whatcom cities and the county are flagged for review by hand. Other counties are coming. All results are estimates, not legal, tax, or appraisal advice.
