1. Every figure starts at the primary source
I do not use third party aggregators, comparison sites or secondary summaries for tax bands, thresholds or rates. Each calculator is built directly from HMRC and gov.uk guidance, and from gov.wales or revenue.scot where a calculator covers Wales or Scotland specifically. The exact page or guidance document used is named in that calculator's own Sources section, with the date it was checked.
2. Built and checked by an accountant, not just coded
Because I am ACCA qualified, I check each calculator's underlying logic the same way I would check a real client calculation, including the edge cases that a simpler tool can miss, such as thresholds, tapers and nation specific rules. A calculator on MySums is not just a formula someone typed once. It is checked, then checked again against a worked example by hand before it goes live.
3. Reviewed on every rate change, not just at launch
UK tax years, National Insurance thresholds and pension allowances change constantly, and sometimes mid year. Every calculator carries a last reviewed date, and I go back through the underlying figures whenever a new tax year or Budget changes them. A calculator that has not been touched in a while has usually not needed to be, not been forgotten.
4. The working is shown, not hidden behind a number
Every calculator page explains the formula behind the result in plain language, with at least one worked example using real numbers. The point is that you can follow the logic yourself, or spot check it, rather than being asked to trust a black box.
5. Scope is stated honestly
MySums gives general, illustrative estimates for planning purposes. It does not replace a payslip, a pension statement, or advice from a regulated financial adviser or accountant for a decision you are actually relying on. Each calculator says plainly what it does and does not cover, particularly where the topic sits close to advice territory, such as pensions or property tax.
6. Corrections happen quickly
If you spot a figure that looks wrong, tell me. I treat every report as worth checking properly, and if something needs fixing, it gets fixed and the reviewed date is updated, not quietly left. The full process, including how quickly you get a reply, is set out in our editorial and corrections policy.
Sources used across MySums
Depending on the calculator, MySums draws on:
- HM Revenue and Customs and gov.uk, for Income Tax, National Insurance, pensions and Stamp Duty Land Tax guidance
- The Welsh Revenue Authority (gov.wales), for Land Transaction Tax
- Revenue Scotland and the Scottish Government (revenue.scot, gov.scot), for Scottish Income Tax and Land and Buildings Transaction Tax
- HM Land Registry, for registration fees
- NHS Employers, for Agenda for Change pay scales and annual leave entitlement
- The Office for National Statistics and Brightmine, for pay benchmarking data on relevant calculators
Each calculator page lists the specific sources it relies on, with the date they were last checked, in its own Sources section.