Numbers you can check, from someone who models EVs for a living

The name says it plainly: WattsDue tells you what is due, in tax and in charging costs, when you run an electric car.

WattsDue is an independent research project in electric vehicle economics. It is built and maintained by a researcher working in battery electric vehicle powertrain simulation. The work behind this site involves building physics-based models of EV powertrains and validating them against laboratory dynamometer measurements. That discipline shapes every tool here: a number is only published once it can be traced to a source and reproduced.

Research method

Each calculator follows the same three-step method. First, the governing rule or physical relationship is identified from a primary source, such as legislation, official consultation documents, electrical codes, or manufacturer specifications. Second, the calculation is implemented and tested against worked examples with known answers. Third, the assumptions are stated openly on the page, so any reader can check the arithmetic independently.

These calculators apply that same standard to the money side of EV ownership. Every rate, threshold, and date on this site comes from primary sources. These include IRS guidance, GOV.UK consultation documents, HM Treasury Budget papers, and House of Commons Library briefings. Each tool states its assumptions and links to its sources, so you can verify the arithmetic yourself.

Editorial policy

Tax rules in this area are moving quickly on both sides of the Atlantic. Pages carry an updated date. When a rule changes, the affected calculator and its explanation are revised. If you spot an error or an out-of-date figure, please tell me via the contact page; corrections are made promptly.

What this site is not

Nothing here is tax, legal, or financial advice. The calculators produce estimates under published rules and proposals; your personal position may differ, and you should confirm decisions with a qualified professional.

Advertising

The site may display advertising to cover its running costs. Advertisers have no influence over the calculators, the figures, or the editorial content.