One of the first questions I hear from homeowners thinking about a single/double storey extension is: “What is it likely to cost?” It is a perfectly reasonable thing to want to know before you speak to an architect, approach a builder, or make any kind of commitment. To help with exactly that, I have built an online tool called ExtendIQ.

ExtendIQ is a UK house extension cost calculator that gives you an instant indicative cost range based on your specific circumstances. You adjust the Gross internal floor area (GIFA) (anywhere from 5 to 100m²), choose a specification level — Basic, Good, or High Spec — select your UK region, and tick any relevant add-ons such as a kitchen, bi-fold doors, skylight, underfloor heating, a WC, or planning fees. The calculator returns a realistic Low–High cost range in seconds.

If you want to go further, a full detailed breakdown, build programme, market rate comparison, and a branded PDF report are available for £10 — useful if you are at the stage of budgeting seriously or comparing quotes. Click on the image below for access to the calculator.