The reference proposal in this series starts above £10 million of individual net wealth, counted per person and net of relevant liabilities. Advani, Hughson and Tarrant, in Fiscal Studies in 2021, count 22,000 people above that line.
That is 0.04 per cent of UK adults.
Everybody else files nothing, values nothing and hears from nobody. The objection behind the question pictures a different country, one that stops each January to price its own possessions.
The objection at full strength
An annual charge needs an annual number, and the assets that carry someone past £10 million are often the ones with no number attached. A house has a price on the day it sells. A private company has none on most days of its life, and two competent valuers working from the same accounts will produce different figures, each of them defensible.
All of it turns on one word, which is annual. A number produced for a transfer tax is produced once, at a death or a sale, and the argument about it ends when the transaction does. A number produced for a wealth tax has to be produced again the following January, and any disagreement about the method arrives again with it, for as long as the asset is held.
Norway's Ministry of Finance told the Wealth Tax Commission's researchers that a wealth tax raises more challenging valuation issues than other taxes, for taxpayers and for the tax authority alike.
The objection has a government behind it.
Filing and valuing are different jobs
The question runs two burdens together, and they behave differently. Above a threshold of £10 million the practical issue is which holdings need somebody's opinion and which need a printout.
Listed shares, funds, bonds and cash carry a price that already exists, published by somebody else and printed on a statement the owner receives anyway.
Reporting them is transcription.
The judgement is required elsewhere: private businesses, land, buildings held off the market and art, along with anything else that changes hands once in a decade. That is where the cost sits, and how often each of those has to be priced is a choice the design makes.
What the exercise is estimated to cost
The serious UK estimate comes from the Wealth Tax Commission's own cost work. Burgherr's background paper for the Wealth Tax Commission, published in 2020, puts taxpayer compliance costs for a well-designed wealth tax at about 0.1 per cent of taxable wealth as a central estimate, with a lower bound near 0.05 per cent. That lower figure is roughly what taxpayers already spend complying with the Annual Tax on Enveloped Dwellings, which Burgherr notes is in principle a simpler charge to administer.
Read the denominator carefully. It is taxable wealth, so on its own the figure says nothing about the size of the bill sitting beside it.
Set against the charge instead, the paper's worked case is a 1 per cent wealth tax, where compliance costs of 0.1 per cent of taxable wealth come to 10 per cent of the charge. At the 2 per cent rate this series argues for, the same estimate implies about 5 per cent. The 5 per cent version is our own arithmetic; Burgherr publishes the 1 per cent case.
The limits of that number
Burgherr's estimate is a model output for a tax nobody has run, assembled from the costs of taxes that do exist. Nothing in operation can confirm it or contradict it.
It also measures one side of the ledger. Compliance cost is what taxpayers spend; what a revenue authority spends running the tax is a separate figure, estimated separately in the same paper, and it is the one that lands on the Exchequer.
When the Wealth Tax Commission wrote to Norway, Spain and Switzerland to ask what their wealth taxes cost to administer, it obtained indicative evidence and no more. Norway's Ministry of Finance held no separate reports or estimates. The Swiss Federal Tax Administration held no information on those costs, because the tax there is levied by the cantons and the municipalities.
So the cost of a wealth tax is design-dependent, and it is not credibly quantifiable in advance. It turns on the breadth of the base, the threshold, the valuation rules, the revaluation cycle, the size of the filing population, the dispute process and the treatment of taxpayers who cannot pay. Any confident number, from either side of this argument, is a model output.
Frequency is a design choice
Not every asset has to be repriced every January. Listed holdings and cash arrive with a current price attached. Property can sit on a revaluation cycle, with years between appraisals.
Unlisted shares can be carried between events by a statutory formula, which is what Spain does. Where a company's accounts are unaudited, or the audit opinion is not favourable, article 16 of Ley 19/1991 takes the greatest of the nominal value, the theoretical value from the last approved balance sheet, or the average profits of the three preceding closed financial years capitalised at 20 per cent, which works out as a multiple of five. The taxpayer starts from a number, the authority defends the same number, and the argument that follows is about the inputs.
That was the statute as read on 12 August 2026. Wealth-tax rules abroad are amended often, and no provision here should be relied on without checking its date.
A formula costs something.
No operating design has yet achieved accurate annual valuation, low administrative cost, neutrality between asset classes and full liquidity protection at the same time. Spain's article 16 buys cheapness, and a figure both sides can argue over using documents that already exist, at the price of accuracy.
The revaluation cycle is one of the levers listed above, and setting it is a decision about how much error to accept between one appraisal and the next. A long cycle is cheap and stale. A short one is current and expensive. Choosing is unavoidable, and a cost estimate that does not say which choice it assumes is not telling you much.
What a threshold is for
A threshold is normally argued as a fairness question. It also fixes the size of the filing population, and every pound it comes down by adds people whose assets somebody has to look at.
Headcount is only part of that. The filing population and the dispute process are two of the drivers the cost of the tax turns on, and they move together: more filers means more assets that need an opinion, and more opinions means more arguments to run.
At £10 million that population is 22,000 people, 0.04 per cent of UK adults. The holdings inside it that need judgement rather than transcription belong to a group small enough to give a specialist unit, working to rules that decide in advance how often each class of asset is priced.
How much valuation a wealth tax needs is settled by where the threshold sits, long before anybody opens a file.
Sources and evidence status
Advani, A., Hughson, H. and Tarrant, H., Revenue and distributional modelling for a UK wealth tax, Fiscal Studies 42(3-4), 2021, Table 1 (KB-058); ONS mid-2024 population estimates for the denominator (KB-003). Burgherr, D., The costs of administering a wealth tax, Wealth Tax Commission Background Paper no. 126, 2020 (KB-087, KB-088, KB-089, KB-091, KB-092). Ley 19/1991 del Impuesto sobre el Patrimonio, Art. 16 (KB-084). Comparative design position on valuation, cost, neutrality and liquidity: KB-042. Threshold and rate of the model this series references: a policy proposal, not enacted law (KB-002, KB-001).
The headcount is a T1 Verified Fact taken from a peer-reviewed table, and the 0.04 per cent share is arithmetic on it against the ONS adult population. The compliance-cost figures are T3 Modelled Estimates for a well-designed tax, built from analogues in existing UK taxes, and the 5 per cent ratio at a 2 per cent rate is our own calculation from the published 1 per cent case rather than a figure the paper prints. The Spanish valuation rule is a T8 Legal or Regulatory Statement verified against the statute on 12 August 2026 and current at that date. No jurisdiction operating a wealth tax publishes an administration cost that would confirm or refute the compliance estimate, and this article asserts no figure for what a UK wealth tax would cost to run.
Nothing here is tax advice.
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