There is no single income rule for every benefit
Means-tested support such as Universal Credit, Housing Benefit and Council Tax Reduction all look at income, but they do not always count exactly the same things in exactly the same way. Contribution-based benefits such as New Style JSA and ESA work differently again.
That is why a general guide is useful. It helps people understand the categories before they try a calculator.
Earnings, pensions and some benefits can reduce support
Wages usually matter most for working-age means-tested support. Private pensions can matter more on ESA or Pension Credit. Some benefits count as income for other schemes, while disability benefits are often treated more favourably.
If an estimate looks low, checking the income treatment is often more useful than checking the headline rate.
Adjusted net income is a different concept
Tax-based charges such as HICBC use adjusted net income rather than the same income definition used in most means-tested benefits. That distinction catches people out regularly.
The site therefore keeps those pages separate rather than mixing the terms.