Valuing a home from comparable sales: a practical method

Valuing a home from comparable sales is the method surveyors use, and there is nothing about it that requires a qualification to attempt. It requires evidence, a spreadsheet, and the discipline to stop at a range rather than pretending to a single number. Done properly it will get you close. Done carelessly, it produces a figure with false authority, which is worse than having no figure at all.

What makes a sale comparable

• Location. The same street beats the same postcode, which beats the same district. Crossing a main road, a railway line or a catchment boundary usually crosses a price boundary too.
• Type. Compare terraced with terraced, flat with flat. A semi-detached house is not a small detached house.
• Tenure. Never mix freehold and leasehold, for the reasons set out in leasehold vs freehold in the sold price record.
• Size. Within roughly twenty per cent of the subject floor area, otherwise the price per square metre relationship starts to bend.
• Date. Within six to twelve months if you can, and adjusted if you cannot.
• Category. Standard category A entries only. Repossessions and transfers to buyers who are not private individuals belong in a different analysis.

Six comparables meeting most of those tests beat twenty that do not. If the street cannot produce six, widen carefully, one criterion at a time, and write down which one you relaxed. A valuation you cannot explain is a valuation you cannot defend when the seller pushes back.

The method, step by step

1. Pull every sale on the street and the adjoining streets for the past eighteen months from the sold price records.
2. Strip out the entries that fail the comparability tests above, keeping a note of why each one went.
3. Find a floor area for every survivor, and for the subject property, from the energy certificate register.
4. Convert each sale to a price per square metre. This is the step most people skip and the step that makes the exercise work.
5. Adjust older sales forward to today using a published regional index for the same months.
6. Adjust for visible differences: an extension, off-street parking, a converted loft, a garden of a different size, a top floor flat against a ground floor one.
7. Take the median of the adjusted figures, note the range, and multiply the median by the subject floor area.
8. Sanity check the result against the asking prices of anything currently on the market nearby, and against the previous sale of the same property, indexed forward.

Finding the missing denominator

Price Paid Data contains no floor area, so step three has to come from elsewhere. The energy certificate register is the practical answer: certificates are required when a home is marketed or let, they are public, they are searchable by address and free, and each one records a total floor area along with the age band and the heating type. Most homes that have changed hands since 2008 have one.

Handle the figure with a little care. Floor areas on certificates are measured to a convention by an assessor working quickly, and they can disagree with an agent brochure by a noticeable margin, particularly where a conservatory, a converted garage or a room in the roof is involved. Where two sources conflict, prefer the one you can verify, and if the whole valuation turns on three square metres, the valuation was never that precise.

Adjusting for the passage of time

A sale from eighteen months ago is evidence about eighteen months ago. To use it now, index it forward with a published mix-adjusted index for the region or local authority, taking the ratio between the index value for the month of sale and the most recent settled month.

Purely as an illustration of the arithmetic: if the index stood at 100 when the comparable sold and stands at 104 now, a sale at £300,000 indexes to £312,000. The figures are invented to show the calculation. Use the actual series from the UK House Price Index reports, and prefer the most local geography the index publishes, since regional and national movements can differ sharply from a single town.

A worked example

Four adjusted figures clustered between roughly £3,830 and £4,120 per square metre give a median close to £3,975. Applied to a subject property of 80 square metres, that suggests something in the region of £318,000, with a defensible range of about £306,000 to £330,000 given the spread. The range is the honest output. The single number is what you say out loud when someone insists.

Sanity checks, and when to stop

1. Does the figure sit inside the historic range of the street, and if it sits above the highest sale ever recorded there, can you say why?
2. Does the previous sale of the same property, indexed forward, land anywhere near your answer?
3. Would removing your single best comparable change the conclusion? If it would, you do not have enough evidence.
4. Have you checked the sample for the traps in reading local price trends, particularly small samples and provisional recent months?
5. Is anything currently on the market nearby priced in a way that flatly contradicts you?

There are situations where this exercise is not enough and a professional valuation is the right answer: probate, divorce, a shared ownership staircasing calculation, a company purchase, an unusual or listed property, or anything where a formal figure will be relied on by a third party. A mortgage valuation is not a substitute, since it is prepared for the lender rather than for you. The Royal Institution of Chartered Surveyors publishes the standards those valuations follow and lists qualified firms.

Sources: comparable evidence is HM Land Registry Price Paid Data for England and Wales, covering roughly 30 million transactions since January 1995 and updated monthly around the 20th; floor areas come from the find an energy certificate service. Contains HM Land Registry data © Crown copyright and database right 2026. This article is general information and not a valuation or professional advice.