It's from the Office for National Statistics. (based on pre Covid)
www.ons.gov.uk/visualisations/dvc1802/calculator/index.html
It uses the OECD equivalised disposable income - so basically it looks at your household and determines the relative income needed. Some people might take umbrage at this - especially with the increase in energy bills. The idea is that certain households need more income for the same lifestyle compared to a household with fewer people in.
For example - a household with 2 adults would need an income that is 1.5 x bigger than a household with a single adult in to maintain a similar lifestyle.
It doesn't take into account situations like separated parents, chilldren being away at Uni, but it does give an indication.
I think it might surprise some people where there income and savings are. But then again, a high income in some places is offset by a high mortgage.
The equivalised income is used in all set of datasets when looking at poverty.
Turns out I am doing ok...which has surprised me.