Post-Renovation House Value Estimator

On a £600,000 terraced house in Dulwich we estimated around £72,000 in uplift from a rear kitchen extension. That's the 12% figure the calculator uses, capped so it doesn't run wild on high-value properties. In practice I've seen buyers pay £50,000 to £80,000 more for a property with a done extension versus one that still has the galley kitchen. The real driver isn't the square footage alone, it's the open-plan kitchen-diner that London buyers expect. A basic rear extension at £65,000-£75,000 all-in will typically add more than it costs in south London. Dulwich, Clapham, and Battersea tend to return more than Croydon or Catford because the buyer pool is larger and they value spec more.

Depends on your starting point. If you're already a four-bed house, another bedroom from a loft adds less than it does to a three-bed, where the jump from three to four beds is significant. I did a loft on a three-bed semi in Streatham last year. £55,000 build, added a bedroom and en-suite, and the owner got three offers over asking. That's not a coincidence. The 18% uplift figure in this calculator is a realistic ceiling for that kind of conversion. Kitchen extensions add lifestyle value to buyers who work from home or have young kids. Lofts add bedroom count, which has a direct effect on Rightmove search filters. Both can outperform the cost. It depends what the house is missing.

Directionally right, not precisely right. The percentages come from Land Registry transaction data and estate agent analysis for south London boroughs, not random figures. But a £900,000 house in Kensington won't respond to a new kitchen the same way a £450,000 terrace in Lewisham does, hence the caps. The borough multiplier adjusts the uplift up or down based on where demand sits. What this tool won't capture is a property in poor condition where the uplift will be higher because the baseline is low, or a property that's already been extensively done where each additional improvement adds less. Use this as a starting figure, then talk to an agent who knows your specific street.