How Will the VOA Value My Home for the Mansion Tax?

If you own a home anywhere near £2m, how the Valuation Office Agency (VOA) will value your home for the mansion tax matters more than the tax rates themselves, because the valuation decides whether you pay at all. As of August 2026, everything we know comes from the government's High Value Council Tax Surcharge (HVCTS) consultation document, published on 19 May 2026. The consultation closed on 14 July 2026 and the government's response has not yet been published, so every detail on this page is a proposal, not law. But the consultation is specific about the method, and it tells owners near the threshold exactly what to prepare for.

How will the VOA value my home for the mansion tax?

The consultation proposes a model-assisted valuation: an automated valuation model (AVM) estimates each home's 2026 market value first, and a VOA valuer then reviews that estimate at a desk before the property goes on the list. For the vast majority of homes there will be no visit and no inspection. This is the only realistic way to value at scale: the Office for Budget Responsibility expects around 165,000 English homes to be over the £2m threshold, roughly 66% of them in London and 22% in the South East.

Two things follow from that design. First, this is not a council tax revaluation. The surcharge is a standalone exercise on 2026 values, completely separate from the 1991-based band list, so your current band neither triggers nor protects you. Second, a desk valuation can only be as good as the data on the desk, which is why the weaknesses of AVMs (covered below) matter so much to owners near a threshold.

Which? reports that the Valuation Office will screen properties it estimates at £1.5m and above, casting the net well below £2m so that borderline homes are not missed. That screening figure has not been confirmed by the government, but it is a sensible working assumption: if your home is worth anywhere upwards of about £1.5m, expect the VOA's model to look at it.

Charges would rise with CPI from 2029-30, but the value thresholds would not be automatically uprated. The valuation itself would be refreshed every 5 years, with the next revaluation proposed for 2033, so the number the VOA settles on for 2026 sticks to your home for a long time.

Will the VOA visit my house?

Almost certainly not. The proposed process is desk-based from start to finish: the AVM produces the estimate, a valuer sense-checks it against the data available, and physical inspections are reserved for the minority of cases that cannot be resolved on paper. That keeps the exercise cheap and fast for the VOA, but it cuts both ways for you. A valuation done from a desk cannot see an unmodernised interior, a structural problem, or anything else that makes your home worth less than the data suggests. Those factors only enter the valuation if you put them there, through the challenge process, with dated evidence.

What is the valuation date for the mansion tax?

The consultation fixes valuations to 2026 market values, though the precise antecedent valuation date within 2026 had not been confirmed as of August 2026; expect the government response or the legislation to pin it down. The principle is the same one council tax uses with 1 April 1991: every home is valued as at a single common date, so the question is never "what is my home worth today" but "what was it worth in 2026".

This matters enormously for evidence. When the draft list appears in late 2027 and you want to argue your home was under £2m, a 2027 or 2028 sale price does not directly answer the question. What counts is 2026-dated evidence: sales of comparable homes that completed in 2026, your floor area as it stood in 2026, and the condition of the property in 2026. That evidence exists in abundance right now and gets harder to reconstruct with every month that passes.

What data will the AVM use?

AVMs estimate value by combining recorded facts about your home with local price evidence. Based on how these models work and the data the VOA holds or can access, expect the inputs to include:

• Sold prices. HM Land Registry records every transaction. Sales of homes like yours, on your street and in your area, are the backbone of any AVM estimate.
• Floor areas. Internal area, largely from Energy Performance Certificate records and the VOA's own survey data. Price per square metre times your floor area is the core of most estimates.
• Property attributes. Type (detached, semi, terrace, flat), age, bedrooms, plot and outbuildings, drawn from VOA records, EPCs and mapping data.
• Local price levels and trends. House price indices to adjust older sales to 2026 values.

How accurate are automated valuations?

Good on typical homes, unreliable on unusual ones. An AVM is accurate where the data is rich: a common house type on a street with plenty of recent sales. It struggles exactly where £2m-plus homes live: one-off properties with few true comparables, large plots, and homes whose value depends on things no database records. The known blind spots are:

• Unusual homes. Period one-offs, conversions and architect-designed houses have few genuine comparables, so the model leans on averages that may not fit.
• Unmodernised interiors. The data says 5-bed detached; it cannot say the kitchen is from 1978. Condition can swing a £2m valuation by hundreds of thousands.
• Plot quirks. Odd-shaped gardens, shared access, overlooked aspects and short leases are invisible or poorly captured in attribute data.
• Recent problems. Subsidence, damp, cladding or roof issues arising near the valuation date will not be in any dataset the model reads.

The consultation implicitly accepts all of this: the valuer desk review exists because AVM output is not trusted on its own, and the OBR's costing assumes 20% of affected owners will challenge and 40% of those challenges will succeed. In other words, the government's own forecaster expects a meaningful share of the first list to be wrong.

What should I do now if my home is near the £2m threshold?

Build your own 2026 evidence file while the evidence is easy to collect. Challenging the valuation will be free through the official process, and the owners who win will be the ones holding 2026-dated proof the AVM never saw:

1. Record your floor area. Check your EPC's stated internal area and keep any measured floor plans. If the EPC overstates your size, that error feeds the model; get it corrected.
2. Collect 2026 sold comparables. Note same-type homes near you that sell during 2026, with address, date and price. These become the core of any challenge.
3. Photograph condition, with dates. Unmodernised rooms, structural issues, anything that drags value below what a clean data profile suggests. Timestamped photos taken in 2026 are far stronger than 2028 recollections.
4. Document quirks. Short lease terms, shared access, restrictive covenants, flood history: keep the paperwork together.
5. Diary late 2027. The draft list is due then, and the proposed 8-month initial challenge window starts running when it lands.

When is the draft list published, and how do I challenge?

Under the proposed timeline, the Valuation Office publishes a draft list of in-scope properties in late 2027, ahead of the first bills in March 2028 for the 2028-29 year. When the list lands there would be an 8-month initial challenge window, then a 6-month standard window after that; the VOA would have to respond within 4 months, with a further 3 months to appeal to the Valuation Tribunal for England, and you would keep paying while a challenge runs. The full process, evidence standards and deadlines are covered in our guide to challenging a mansion tax valuation, and the policy itself in our mansion tax explainer.

One honest note on where we fit. Challenging the surcharge valuation will be free through the VOA, exactly as council tax band challenges are free today. Council Tax Challenger's £9.99 evidence pack covers council tax band challenges, not the mansion tax. But the two overlap for many owners: most homes in surcharge territory sit in bands F, G and H, and if the 1991 band itself is wrong you may be overpaying now, years before any surcharge bill. Checking your band takes a minute and costs nothing.