Editorial policy
How we choose our figures, check our calculators and keep them up to date.
Where our figures come from
We use the most official source available, in this order:
- Regulators and government: Ofgem, HMRC, GOV.UK, the Highway Code and devolved governments.
- Independent bodies: the Energy Saving Trust, Which?, PDSA and The Kennel Club.
- Manufacturers and UK suppliers, for product sizes, coverage and power ratings.
Where sources disagree, we use the official figure, or the middle of the range and say so on the page. Every calculator lists its sources, with links, in its "About this page" box.
How we check a calculator
- We write out the method in plain English on the page, under "How we calculate this", so you can check it yourself.
- Before a page goes live, we work through example sums by hand and test that the calculator gives the same answers, including unusual inputs.
- If we can't find a reliable source for a figure, we leave it out rather than guess. A calculator that can't be checked properly isn't published.
How pages are made
Pages are written and checked by Steven Stewart. We use software tools, including AI, to help draft text and build the calculators. Every figure, formula and claim is checked by a person against the listed source before it goes live, and we take responsibility for everything we publish.
How we keep figures up to date
Figures that change on a schedule are updated when the new numbers are published. The site is built so that it can't be published with an energy price period or tax year that has ended. Here's what we track:
| Figures | Source | How often | Last checked |
|---|---|---|---|
| Energy prices October to December 2026 | Ofgem energy price cap | Every quarter, when Ofgem announces the next cap | 20 October 2026 |
| Fuel prices week ending 11 October 2026 | Weekly UK pump prices from government Fuel Finder data | Every month | 20 October 2026 |
| Mileage rates 2026 to 2027 tax year | HMRC approved mileage rates | Every tax year | 20 October 2026 |
| Appliance power and use | Energy Saving Trust, Which? and manufacturer specifications | At least once a year | 20 October 2026 |
| DIY sizes and coverage | Manufacturers and UK suppliers, such as British Gypsum, Dulux and Marshalls | At least once a year | 20 October 2026 |
| Pet timelines | PDSA, The Kennel Club and UK vet practices | At least once a year | 20 October 2026 |
Every update is listed on the changes page.
Corrections
If you think something is wrong, email [email protected] with the page and what looks wrong. We check it against the source, usually within a few days. If we've made a mistake, we fix it, update the page's checked date and record the change on the changes page.
Funding and independence
Numwise is free to use. It has no adverts, sponsors or paid links at the moment. If we add adverts or links that pay us a fee in future:
- they will be clearly labelled;
- they will never change a calculator's result or the figures we use;
- no company can pay to be included, ranked or left out.
Limits
Our results are estimates to help you plan and budget. Your real costs depend on your supplier, your home, the products you buy and how you use them. For decisions about your health, your pet's health, your taxes or building work, check with a qualified professional. See our terms of use.