Honest answer: as accurate as the numbers you put in. Here's exactly how they work.
Every tool on this site uses simple, published arithmetic — no black boxes, no "proprietary models". This page sets out the formulas, the assumptions behind the defaults, and the things we deliberately leave out so you can judge the results for yourself.
Countries that use miles, MPG or dollars-per-gallon are converted internally at exact factors (1 mile = 1.609344 km; US gallon = 3.785 L; imperial gallon = 4.546 L), so the maths is identical everywhere.
Defaults are drawn from public national data for the country you select — energy regulators, government emissions factors and motoring-body fuel monitors (AER, ACCC and the National Greenhouse Accounts in Australia; MBIE and the AA in New Zealand; Ofgem and RAC in the UK; EIA and AAA in the US, and so on). Each calculator links its sources. They're national averages from 2026 data — a sensible starting point, not your bill.
Purchase price, depreciation, insurance, registration, servicing and tyres. These vary so much by model and driver that including "averages" would create false precision. Most calculators answer one question well — what does the energy cost? — and leave whole-of-life comparisons to you. The one exception is the break-even tool, which exists precisely to weigh the purchase premium against those energy savings (it still excludes depreciation, and says so). Two known gaps worth flagging: New Zealand EVs pay Road User Charges (~$76 per 1,000 km) that aren't included, and time-of-use tariffs mean your effective rate depends on when you charge.
If you use the defaults, treat results as a solid ballpark — typically within 10–20% for the energy-cost comparisons, driven mostly by how much electricity and fuel prices vary around the national average. If you enter your own tariff, your car's real consumption and your local fuel price, the arithmetic itself is exact; the remaining uncertainty is just how your driving varies month to month.
Prices move — especially fuel. We review the defaults periodically against the sources above and bump the figures when they drift. If you spot a number that looks out of date, we genuinely want to know: tell us via the contact details on the homepage.
