Mobile Tax-Base Stress Test
Test a tax proposal against mobility, avoidance, and second-order effects
- Difficulty
- Advanced
- Time to result
- ~months to results
- Steps
- 6
- Confidence
- 86%
Across the debate, Daniel Priestley repeatedly separates what sounds fair from what a government can practically implement. The stress test begins by defining whether a proposal taxes income, realized gains, unrealized wealth, profits, revenue, property, or consumption. It then divides the base into mobile and immobile parts, maps relocation and profit-shifting options, and estimates how owners, firms, investors, workers, and consumers may respond. Only after those responses does it estimate net revenue and distributional effects. Gary Stevenson challenges the conclusion that mobility makes taxation futile, pointing to immobile land, local customers, and the possibility of taxing activity where sales occur. The framework therefore works best as a structured contest between a proposal and its avoidance routes, not as evidence for either speaker's preferred policy.
Origin
Extracted from The Diary of a CEO
Core principles
- 01Separate moral aims from implementable mechanisms
- 02Distinguish mobile wealth from immobile assets and local sales
- 03Model behavioral responses before counting revenue
- 04Assess who ultimately bears the cost
- 05Compare net outcomes, not headline tax rates
How to run it
- 1
Define the base
State exactly what is taxed: income, gains, wealth, profit, revenue, consumption, land, or inheritance. Specify thresholds, jurisdiction, and timing.
Watch out Do not compare unlike taxes as though they were the same annual charge.
- 2
Classify mobility
Separate people, intellectual property, headquarters, profits, customers, buildings, and land by how easily each can move or be reassigned.
Pro tip Treat mobility as a spectrum rather than a yes-or-no label.
- 3
Map response options
List lawful relocation, restructuring, valuation, realization, and profit-allocation responses available to affected parties. Include the cost and time required for each.
Watch out Do not assume every taxpayer responds identically.
- 4
Estimate net collection
Model the tax collected after plausible departures, avoidance, valuation changes, and enforcement costs. Use ranges rather than one confident number when evidence is uncertain.
Pro tip Show the break-even response rate that would overturn the proposal's expected gain.
Watch out A back-of-the-envelope estimate is a starting point, not a fiscal forecast.
- 5
Trace incidence
Assess whether costs remain with owners or shift to prices, wages, investment, tenants, or other taxpayers. Test both short- and long-term effects.
Watch out The legal payer and the economic bearer may differ.
- 6
Compare enforceable designs
Compare the original proposal with alternatives anchored to less-mobile bases or stronger reporting rules. Preserve the policy objective while reducing avoidable leakage.
Pro tip Include a no-change baseline so every option faces the same test.
In the wild
The speakers debate a proposed annual charge on wealth above £10 million. Priestley argues that owners and digital companies could relocate or restructure, while Stevenson argues that local revenue, land, and property remain taxable and that difficulty is not a reason to abandon the objective. A stress test would define valuation rules, estimate relocation and collection ranges, identify immobile bases, and compare the net result with alternatives.
→ A transparent estimate of collection, leakage, incidence, and enforcement trade-offs rather than a fairness claim alone.
The debate uses global platforms selling to British customers while allocating profits elsewhere. The test would map where customers, revenue, intellectual property, and reported profit sit; identify licensing and transfer-pricing routes; and assess whether a sales-linked or destination-based rule is more enforceable. The episode does not resolve which design is legally or economically best.
→ A comparison of tax designs based on enforceability and likely behavioral response.
Common mistakes
Equating fairness with feasibility
A morally attractive objective can still have a weak mechanism, while a feasible mechanism can still be judged unfair.
Counting revenue before behavior
Multiplying a rate by today's tax base ignores relocation, restructuring, valuation, and enforcement responses.
Calling all wealth mobile
Land, buildings, customers, and locally generated activity may be harder to move than owners or intellectual property.
Is it for you?
Best for
It is best for taxes affecting globally mobile owners, digital firms, intellectual property, property, or cross-border revenue.
Not ideal for
It is not ideal as a substitute for empirical modeling, legal analysis, or a political judgment about fairness.
From the transcript
“it's not about fairness it's about pragmatically what can you get away with”
“the problem is wealth is completely mobile now”
“their revenues can't their customers are where their customers are”
From the episode
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