How our figures work
Sources last checked: 28 September 2026 (tax rates and thresholds) and 30 October 2026 (fuel prices and duty)
Every CalcIt calculator runs on published UK rates and thresholds. This page sets out where those figures come from, how often they are checked, how results are rounded, and how to report a mistake.
Where the figures come from
We use primary sources: GOV.UK pages published by HMRC and other government departments, legislation on legislation.gov.uk, and official statistics from the ONS, DESNZ, DfT and Ofgem. We do not take figures from other calculator sites.
Budgets and new tax years
Most UK tax rates change on 6 April, the first day of the tax year, and are announced at the Budget before it. Each calculator says which tax year it covers. The 2026/27 rates were last checked against the sources above on 28 September 2026.
Fuel duty follows Budget 2026: 52.95p a litre until 30 June 2027, then 60.59p a litre from 1 July 2027 (Annex A of the Overview of Tax Legislation and Rates). When the Budget changes a rate, the calculator and its guide are updated together.
How often figures are checked
- Tax rates and thresholds: at the start of each tax year and after every Budget or other fiscal event.
- Pump prices: from the DESNZ weekly series. Every fuel page names the week its prices come from.
- Inflation: ONS annual averages. The current year uses the most recent month ONS had published when the page was last updated (September 2026, fetched 30 October 2026), and the inflation page names that month.
One source for each figure
A figure that appears in more than one place is stored once and written into each place from there. The petrol price, for example, is held in one table on the fuel cost calculator, and the guides, tables and FAQ answers that quote it are filled in from that table. Automated tests compare every fuel figure on the site against it, so a guide cannot show a different price from the calculator.
Other tests run a calculator's own code against results worked out by hand from the published rates, and against GOV.UK's own worked examples where it publishes them (for example, its capital gains tax, dividend tax and stamp duty examples). These result tests cover the stamp duty, capital gains tax, dividend tax, maternity and paternity pay, redundancy, mileage, student loan, sole trader tax, payments on account, VAT flat rate scheme, inflation, fuel cost, fuel duty rise, compound interest and mortgage overpayment calculators. The VAT, inheritance tax, pension, salary sacrifice and holiday entitlement calculators do not yet have automated result tests. Every page is also loaded in a test browser to check that its scripts run without errors. The tests are run whenever figures are updated.
Rounding and assumptions
Results are shown to the nearest penny or pound, as labelled on each calculator. HMRC rounds some figures to whole pounds at set stages, so a result here can differ from an official figure by a few pence or pounds.
A calculator handles the common case. It cannot see your full tax position, reliefs you could claim, or rules that apply only to you. Where a calculator makes an assumption, such as using the stamp duty rates for England and Northern Ireland, the page says so.
Your figures stay on your device
Calculations run in your browser. The numbers you type are not sent to us or stored. The privacy policy lists everything the site loads.
Corrections
If you think a figure is wrong or out of date, email [email protected] with the page address, the values you entered and the result you expected. We check the figure against its source and correct the page if it is wrong.
Not financial advice
CalcIt gives estimates to help you understand a calculation. It is not financial, tax or legal advice. For a decision that matters, check the figure with HMRC or a qualified adviser. The terms of use have the full disclaimer.