Why the Indices Disagree
The fundamental reason the indices disagree is timing. A house sale involves several stages: listing, offer accepted, mortgage approved, exchange, completion, and registration. Each index captures prices at a different point in this chain. Mortgage-based indices (Halifax, Nationwide) capture prices at approval stage. The ONS/Land Registry captures prices at registration — typically 2-4 months later. Rightmove captures asking prices, which are aspirational rather than actual.
They also use different samples. Halifax and Nationwide only include properties bought with their own mortgages. The Land Registry includes all transactions (cash and mortgaged). Rightmove only includes properties listed on their platform. These different samples can skew results — particularly when the mix of cash vs mortgage purchases shifts.
The Major UK House Price Indices
Each index has strengths and weaknesses. No single one is 'correct' — they're complementary views of the same market from different angles.
| Index | Source | Measures | Lag | Best for |
|---|---|---|---|---|
| Halifax HPI | Halifax Bank | Mortgage approvals | 1-2 months | Early trend signals |
| Nationwide HPI | Nationwide BS | Mortgage approvals | 1-2 months | Early trend signals |
| UK HPI (ONS) | Land Registry + ONS | Completed sales | 3-5 months | Definitive historical data |
| Rightmove HPI | Rightmove | New listing asking prices | Real-time | Seller sentiment |
| Zoopla HPI | Zoopla | Agreed sale prices | 1-2 months | Current agreed prices |
| Acadata | Land Registry data | Completed sales (repeat sales) | 3-5 months | Academic accuracy |
Mortgage-Based Indices: Halifax and Nationwide
Halifax and Nationwide publish monthly indices based on their own mortgage approvals. Because mortgage approval happens before completion, these indices lead the market by 1-2 months. They're useful for spotting emerging trends quickly.
The limitation is sample bias. They only include properties bought with their own mortgages — not cash purchases (which account for about 30% of transactions) or purchases financed by other lenders. Halifax tends to skew slightly higher because it includes more London transactions; Nationwide skews slightly lower with a stronger regional presence.
ONS/Land Registry: The Gold Standard
The UK House Price Index (UK HPI), produced jointly by the ONS, Land Registry, and Registers of Scotland, is the most comprehensive index. It includes all residential transactions — cash and mortgaged — and uses a repeat-sales methodology (comparing the same property's price over time) to control for mix effects.
The downside is lag. Data is published approximately 3-5 months after transactions complete, which means the UK HPI reflects market conditions from several months ago. For historical analysis and long-term trends, it's the most reliable source. For understanding what's happening right now, it's too slow.
Rightmove: Sentiment, Not Reality
Rightmove's index measures new listing asking prices — what sellers hope to get, not what buyers actually pay. Asking prices are typically 5-10% higher than achieved prices, and this gap widens in a softening market. Rightmove's data is valuable as a leading indicator of seller confidence and supply levels, but should never be used as evidence of actual price movements.
What Rightmove data is excellent for is supply analysis. Tracking the number of new listings, stock levels, and time to sell gives a clearer picture of market balance than price data alone. A market with rising stock and lengthening selling times is a buyer's market, regardless of what asking prices are doing.
Using Price Data in Your Research
When researching a specific property or area, combine multiple sources. Use the Land Registry's Price Paid data (available free on gov.uk) to see what similar properties have actually sold for recently. Use Rightmove and Zoopla sold prices for more recent (but less comprehensive) data. Use the indices for broader trend context.
Be cautious about interpreting national averages for local decisions. House prices are fundamentally local — national average movements tell you almost nothing about what's happening on a specific street. Focus on comparable sales within 0.5 miles of the property you're interested in.
Frequently Asked Questions
Which UK house price index is the most accurate? The ONS UK House Price Index, built on Land Registry data, is the most comprehensive because it covers every completed sale, cash and mortgaged, though it lags the market by three to five months.
Why do Halifax and Nationwide indices disagree? They each measure only their own mortgage approvals, so their samples differ and both exclude cash purchases, which means their monthly figures can point in different directions from the same market.
Is Rightmove's house price index reliable? Rightmove measures asking prices, which are seller aspirations rather than achieved prices and typically sit 5 to 10% above what buyers actually pay, so it signals sentiment and supply rather than real price movements.
Which house price data should I use to research a specific area? Use the Land Registry Price Paid data for what similar homes actually sold for, and treat national indices as broad context only, because prices are local and national averages tell you little about one street.
How out of date is the ONS house price index? It is published roughly three to five months after sales complete, so it is excellent for historical trends and long-term comparison but too slow for judging what the market is doing right now.
Key Takeaways
- ✓UK house price indices disagree because they measure different things at different stages of the buying process
- ✓Halifax and Nationwide are fastest but only include their own mortgages — sample bias is real
- ✓The ONS/Land Registry UK HPI is most comprehensive but lags by 3-5 months
- ✓Rightmove measures asking prices (seller aspiration), not achieved prices — don't confuse the two
- ✓For local research, use Land Registry Price Paid data rather than national indices
- ✓Combine multiple sources for a complete picture — no single index tells the full story