Brexit Calculator - GDP Cost Model

A brexit calculator estimates the cost of a Brexit scenario by combining an adjustable GDP-impact assumption with selected one-off public cost inputs. Use it to test how a long-run productivity or GDP estimate translates into annual cost, cumulative cost, and cost per person. It is most useful for comparing assumptions, checking claims in reports or speeches, and separating economic-output estimates from direct government spending.

• • Policy discussion: Model how a 2 percent, 4 percent, or 6 percent GDP-impact assumption changes the implied annual cost.
• • Public finance review: Keep EU Exit preparation spending, the financial settlement, and other one-off costs visible instead of mixing them into GDP loss.
• • Per-person framing: Translate a billion-pound total into a population-adjusted estimate that is easier to explain.
• • Scenario sensitivity: Adjust the realized share of the long-run effect when you do not want to assume the full effect has already arrived.

The calculator does not decide what Brexit has definitely cost. That question depends on the counterfactual, years selected, baseline GDP measure, and whether you are counting lost output, fiscal receipts, departmental spending, or settlement payments. It keeps those choices explicit so the result can be challenged and improved.

For a household view, treat the per-person output only as a scale reference. It is not a bill owed by each resident, and it does not show how costs are distributed across regions, income groups, companies, or public services.

When the modeled total needs to be compared with planned spending categories, the Budget Calculator helps translate large figures into budget lines.

The model starts with baseline annual GDP, then applies the selected impact percentage and realized-effect percentage. That creates an annualized GDP-effect estimate. The calculator multiplies that annual estimate by modeled years, adds one-off public cost inputs, and divides the total by population for the per-person result.

• Baseline GDP: The annual economic baseline, entered in billions of pounds. You can use nominal GDP, a forecast baseline, or another clearly labelled amount.
• Impact percent: The long-run productivity or GDP effect assumed for the scenario. The default follows the OBR-style 4 percent assumption, but users can change it.
• Effect realized: The share of the long-run effect assumed to be present over the modeled period.
• One-off public costs: Preparation spending, financial settlement, and administration inputs that are added separately from the GDP-effect estimate.

Example: assume a £2,300 billion GDP baseline, a 4 percent long-run effect, 60 percent of that effect realized, and 5.43 modeled years. The annualized GDP effect is £2,300bn x 4% x 60%, or £55.2bn per year. Over 5.43 years, that is £299.74bn. Add £38.83bn of one-off public costs and the total modeled cost is £338.56bn.

The per-person output is a scale conversion. With a 67.6 million population denominator, £338.56bn becomes about £5,008 per person. That figure should be read as an allocation of the modeled total, not a household invoice or tax estimate.

According to Office for Budget Responsibility Brexit analysis, the post-Brexit UK-EU trading relationship is assumed to reduce long-run productivity by 4 percent and leave imports and exports around 15 percent lower than if the UK had remained in the EU.

If you compare older public cost figures with current-price totals, the Inflation Calculator can help adjust money values before the comparison.

The most important part of using the calculator is choosing inputs that describe the same question. These concepts help keep the scenario internally consistent.

Do not compare a cumulative GDP-effect number with a single annual budget line unless the time period is clear. A five-year cumulative estimate can look much larger than an annual department budget because it adds several years together.

Likewise, do not add the same item twice. If your GDP-impact assumption already comes from a public finance forecast that includes lower tax receipts, do not add a second tax-receipt loss unless the source separates it.

For reports that quote euro, dollar, or pound amounts side by side, the Currency Converter Calculator is a better place to handle exchange-rate assumptions.

Start with the question you are trying to answer, then adjust only the inputs that belong to that question. The defaults are a starting scenario, not a claim that every source agrees with.

1. 1 Enter the GDP baseline: Use a clearly labelled annual GDP amount in billions of pounds. If you use a forecast baseline, keep the same baseline in every comparison.
2. 2 Choose the impact percent: Use 4 percent for an OBR-style long-run assumption, or enter another sourced estimate for a sensitivity test.
3. 3 Set the realized share: Use 100 percent only if the scenario assumes the full long-run effect is already present for the selected years.
4. 4 Enter the modeled years: Use the period you want to discuss, such as years since the post-transition trading relationship began.
5. 5 Review one-off costs: Keep preparation spending, financial settlement, and administration costs separate so you can include, exclude, or update each item.
6. 6 Read the outputs together: Compare annual GDP effect, cumulative GDP effect, one-off costs, total modeled cost, and cost per person before drawing a conclusion.

For a briefing note, run three rows: a low-impact case, a default OBR-style case, and a high-impact case. Keep GDP baseline and years unchanged so the difference is driven by the impact assumption rather than hidden period or scale changes.

When a scenario asks what the same money might have earned over time, the Investment Calculator can model growth assumptions separately.

This brexit calculator makes a sensitive economic claim easier to inspect by showing the moving parts behind a headline number.

• • Separates cost types: GDP-effect estimates, preparation spending, settlement costs, and administration costs remain visible as different inputs.
• • Supports sensitivity checks: Changing the impact percent or realized share shows how quickly the total changes when assumptions move.
• • Improves public explanations: The per-person output gives a scale reference that can be easier to discuss than a billion-pound total.
• • Keeps sources accountable: Every default assumption should be checked against a named source before it is used in a report or presentation.
• • Avoids a single forced answer: Users can model competing claims without rewriting the calculation or accepting a fixed political framing.

This is especially helpful when a source mixes lost output with public spending. Lost output describes an economic counterfactual; public spending describes money allocated or paid by government.

The calculator also shows when a disagreement is really about assumptions rather than arithmetic. If two people agree on the formula but choose different impact percentages, the difference belongs in the evidence discussion.

For a business-level view of whether higher trade or compliance costs change unit targets, the Break Even Calculator gives a narrower operating model.

Small input changes can create large differences because the model multiplies a percentage effect by a national economic baseline and several years. Review these factors before using the result formally.

• • The calculator does not produce an official forecast. It models the assumptions entered by the user and should be checked against current economic data.
• • The result does not allocate costs across households, regions, companies, or public services. Distribution requires a separate model.
• • The default one-off cost inputs may need updating if a newer public source changes the preparation or settlement estimates.

When using the output, label the scenario clearly: baseline, impact percent, realized share, modeled years, and one-off costs. Without that label, the total can be misread as an official number.

If you are using current prices, consider whether inflation adjustment is needed before comparing the result with an older budget, settlement, or spending figure.

According to National Audit Office EU Exit preparations report, UK government departments spent at least £4.4 billion preparing for EU Exit by 31 January 2020.

According to House of Commons Library financial settlement briefing, the Office for Budget Responsibility estimated the net cost of the Brexit financial settlement at about £34 billion.

If the comparison requires a consumer-price benchmark rather than a general money adjustment, the CPI Inflation Calculator can support that separate check.