How we check our calculators

We want you to be able to trust the numbers. This page explains how each calculator is made and checked before it is published, and what happens when we get something wrong.

Who does the work

CalcSorted.com is run by one person, the site owner. AI helps us research and draft the pages. It doesn’t decide what is published: the owner does.

The owner is not a financial adviser, and no qualified financial professional checks the calculators. That is why each calculator shows its working and states its assumptions, so you can check the result yourself.

Before we write any code

Research. We look at what people search for and at the calculators that already exist. We note what they do well and where they fall short.
A written calculation spec. We write down exactly how the calculator works: the formulas, how it rounds and which numbers it accepts. It also says what happens with unusual inputs, and what the result includes and leaves out.
Owner approval of the spec. The owner reads and approves the spec before any code is written. The code must follow the spec, not the other way round.

Tests

Worked examples. Each calculator has at least five examples worked out by a separate method, such as a standard formula or a spreadsheet. They include unusual cases, like a target that can’t be reached. The calculator must give the same answers.
Rule tests. We test rules that must always be true, across many different inputs. For example, if you buy more shares at a price below your current average, your average must never go up (before fees).
Precise sums. The calculator works at full precision and rounds only the figures it shows you. The page says when figures are rounded.

We run these tests before every release. If one fails, we fix the problem before we publish the change.

A check against another calculator

Before a calculator is released, we enter the same figures into a well-known public calculator and compare the results. We record the date, the figures, both results and the reason for any difference.

An AI check

A separate AI, which did not write the page, checks it against a fixed list. Does the maths match the spec and the stated assumptions? Is there any advice or product steer? Are the notices there? Do the sources support what the page says? Is the English plain?

This is another AI check, not expert verification. It helps us catch mistakes, but it doesn’t replace a check by a qualified person.

Owner approval

The owner reads every page in full and approves that exact version. Approval covers the page, its spec and the code that does the sums.

If any of these change later, the approval no longer counts. The page can’t be published again until the owner approves the new version. Each page shows the date it was last reviewed.

Facts that change

Some calculators may use rates or rules that change, such as a tax rate. Each one links to its official source and shows the date we last checked it. We check it again at least every three months.

Corrections

Every calculator page has a Report a mistake link. You can also contact us. We aim to check reports within 48 hours.

When a mistake is confirmed, we fix it, add a test so it can’t come back, and approve the page again. If a mistake could have changed someone’s result in a meaningful way, we list it below. We say what was wrong, when it was fixed and which page it affected.

Significant corrections: none yet.