The DAT has gone. The method hasn't.

Residual works from the DAT manual's approach in the browser, with every figure sourced and every version reproducible. It isn't a copy: on a few conventions it differs.

The Development Appraisal Tool collection on GOV.UK records that the tool was withdrawn on 20 April 2026 because it “relies on technology that is no longer supported”. Appraisals built in it still need to be checked, reviewed and rebuilt.

From the Development Appraisal Tool User Manual v4.1, Residual takes the three modes (viability assessment, residual land value and affordable housing valuation), the tenures (open market sale, affordable rent, social rent and shared ownership) and a monthly cash flow over up to 240 months. The method page lists the conventions that differ.

Questions

Is Residual the official replacement for the DAT?: No. It's independent software that works from the published manual, and isn't affiliated with or endorsed by Homes England.
Does it give the same answer as the DAT?: Not always. On the DAT's own training exercise, Residual's land value is 0.62% below the DAT's, and three conventions account for the difference. The guide to the DAT's removal shows how.
Can I bring in a DAT file?: Not directly. You re-key the inputs; a schedule of accommodation can be uploaded as CSV or Excel.

The Working panel of Residual's appraisal workspace for the demonstration scheme Harbour Lane: the residual surplus, NPV, IRR and MIRR, the build-up from revenue to surplus, and the first of the assumptions in use with its source. — The Working panel for Harbour Lane, an invented demonstration scheme.

Founding pilot

We're looking for the first three organisations to run a free reconciliation pilot. See the pilot terms.

Try it on a case you know

Send us one past appraisal (redacted is fine, with nothing about individuals) and we'll rebuild it in Residual and send it back.