Mansion tax worked examples

These four homes are illustrations, not real clients. They show how the proposed surcharge could apply in common situations, and where checking the value would or would not make a difference. Figures use the proposed 2028/29 charges, and 20-year totals assume inflation averages 5% a year. They are illustrations, not forecasts, and a review does not guarantee a different band.

1. The house just over the line

A semi-detached house in south-west London. Its owners think it would have sold for about £2.1m in 2026.

• If the Valuation Office agrees: the first band, £2,500 a year, about £82,700 over 20 years.
• Two similar houses on the same street sold for £1.95m and £2.05m in 2026. Theirs has a smaller garden and a north-facing rear.
• Would a review help? Yes. The case for a value under £2m is arguable, and the prize is the whole charge.

2. The flat with the wrong floor area

A mansion block flat in Kensington. Records show 2,100 sq ft because they include a loft room with a low ceiling. The usable area is closer to 1,800 sq ft.

• On the recorded area the model puts it at £3.6m, in the £3.5m to £5m band at £5,000 a year.
• On the usable area, comparable flats in the block point to about £3.2m, in the £2.5m to £3.5m band at £3,500 a year.
• Would a review help? Yes, and early. This is a factual error that can be corrected when the draft list is published, without a formal challenge. The difference is £1,500 a year, about £49,600 over 20 years.

3. The unusual country house

A listed house on a large plot in Surrey, with no close comparable sales in the past three years. A model has little to go on.

• The owners think it would have fetched £4.8m in 2026. A model working from larger, newer houses nearby might put it over £5m.
• At £5m or more the charge is £7,500 a year; below it, £5,000.
• Would a review help? Yes. Listed status, repair liabilities and access all affect value in ways a sales database will not see. The step is £2,500 a year, about £82,700 over 20 years.

4. The home held in trust, comfortably in its band

A family house held by trustees, lived in by one beneficiary. Recent sales suggest about £3m in 2026, well inside the £2.5m to £3.5m band.

• The trustees are liable for £3,500 a year. The beneficiary keeps paying council tax.
• Deferral may well not be available, as it is aimed at owner-occupiers and the trustees are the legal owners.
• Would a review help? Probably not on value, since the home sits well inside the band. The useful work is planning how the trustees fund the charge, and checking the draft list entry when it appears.

Last checked against the government's Budget documents and consultation response on 30 October 2026. The surcharge is being legislated in the Finance Bill 2026-27 and is not yet law. Some detail is still to come in regulations.