Methodology & data

Principles

• Every assumption is editable. Defaults are a starting point. Your utility bill, your insurance quote and your dealer's numbers always beat our averages.
• Show the formula. Each tool ends with a short “How this is calculated” section.
• Round honestly. Specs, prices and rates are rounded public estimates, so we show ranges where the uncertainty is large (insurance, trade-in values, battery health).
• No upsell. No lead forms, no affiliate quote widgets, no paywall.

Where the defaults come from

• Vehicle prices are approximate UK list prices including 20% VAT, and ranges are WLTP figures (what UK cars and brochures show). Only Model 3 and Model Y are sold new in the UK. Check tesla.com/en_gb before you buy.
• Electricity uses typical price-cap unit rates by region, in pence per kWh. Off-peak EV tariffs (often 7–9p for a few hours overnight) can cut charging costs dramatically.
• Petrol is shown in pence per litre, and fuel economy in imperial mpg. Behind the scenes we work in pounds per imperial gallon (4.546 litres), so the maths matches UK brochure figures.
• Motoring taxes: electric cars registered from April 2025 pay £10 VED in year one and then the standard rate (about £195). The Expensive Car Supplement applies in years 2–6 above the list-price threshold. A pay-per-mile charge for EVs (about 3p a mile) is planned from April 2028. MOT costs apply from year three. Tools that need these figures show them as editable fields.
• Insurance is an index relative to a UK average comprehensive premium, adjusted for region, car, driver age and no-claims years.
• Depreciation curves reflect the UK used-EV market, where values have fallen faster than in the US.
• Grants: the Electric Car Grant only covers cheaper cars that meet its criteria, and Teslas have generally not qualified, so tools default grants to £0. Domestic solar and batteries currently carry 0% VAT in Great Britain.
• Temperatures are in °C. Distances and speeds stay in miles and mph.

Reference data last reviewed: .