Why the house price indices disagree, and what each one measures

Every month brings two or three house price stories, and they frequently seem to contradict each other. One says prices are rising, another says they are falling, and both are reported with equal confidence. It is enough to make you conclude the whole thing is unknowable.

It is not. The reports disagree for a simple reason: they are measuring different moments in the same transaction. Once you know which moment each one is watching, they stop contradicting each other and start being useful.

A house sale has stages, and each index taps a different one

Think about what actually happens when a house is sold.

First a seller decides what to ask for it. Later, a buyer's lender approves a mortgage at an agreed price. Later still, the sale completes and gets registered.

Those three moments can be months apart, and the price can differ at each one. An index built on the first will tell you something quite different from an index built on the third, and neither is wrong.

Asking prices

Some indices are built on what sellers are asking when a property is listed.

The Rightmove index, for example, "includes houses that do not subsequently sell and reports only asking prices". That is a genuine limitation and it is their own description of it. A home listed optimistically and never sold still counts.

It is the earliest signal available, so it tells you what sellers currently hope for. It does not tell you what anybody paid.

The lender indices

Nationwide and Halifax each publish an index built from their own mortgage business. As the government's own guidance puts it, these are "based on their own mortgage approvals only and therefore will not include any cash transactions", and they are timelier because lenders "can process them immediately".

Two things follow from that, and both matter.

They are quick, because a lender knows about its own approvals at once rather than waiting for anything.

And they cannot see a cash buyer at all. A house bought without a mortgage is invisible to a mortgage lender's index, however significant that sale was.

The official index

The UK House Price Index is published by HM Land Registry and the Office for National Statistics. It measures completed sales, "at the end of the conveyancing process, rather than advertised or approved prices", drawing on land registrations in England and Wales, Registers of Scotland, and HMRC Stamp Duty data in Northern Ireland.

Crucially it "uses sales data collected on residential housing transactions, whether for cash or with a mortgage", so it sees the whole market rather than one lender's slice of it.

The trade is timeliness. Registration takes a while: "the amount of time between the sale of a property and the registration of this information varies. It typically ranges between 2 weeks and 2 months." So the official figures always describe a market that has already moved on.

It is also the only one of the three published down to local authority level, which is why a figure exists for Gravesham at all.

So which should you believe?

All of them, about different things. The useful question is not which index is right, it is which one answers your question.

• What did houses round here actually sell for? The official index. It measures completions and includes cash buyers.
• What is happening this month? A lender index. It is weeks ahead of the official figures, as long as you remember it cannot see cash sales.
• What are sellers hoping for right now? An asking price index, with the caveat that some of those homes will never sell at that price.

Why this is worth knowing

Because the next time a headline tells you the market has done something, you will know to ask which moment it is describing, and whose transactions it can see.

We have written separately about what the official figures actually show for Gravesham, including the point that within one borough over one year, semi-detached homes and flats moved in opposite directions. A single number, however authoritative, is always a summary of a mixture.

If you would like to talk about what any of it means for a particular property, we are in Gravesend and the first conversation is free and without obligation.

Your home/property may be repossessed if you do not keep up repayments on a mortgage or other debt secured on it.

Source: About the UK House Price Index, HM Land Registry and Office for National Statistics, accessed 13 August 2026. All quoted passages above are from that page.

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