Your claim that 4% now would have been equivalent to 20% then is another escalation of a well worn claim. First it was 8% then 10% then 15% and now 20%. There probably is an answer but not as simple as you and others make out.

6% mortgage rates are equivalent to 25% in 1980, lender claims - Estate Agent Today
Leeds Building Society has pledged to honour any mortgage offers and support borrowers during this period of market uncertainty.

The average pricing on a two-year fixed rate have hit 6.43% and the building society highlights that while this may be lower than the 15% borrowers paid in the 1980s, higher property values and debt makes the current environment more tough![]()
In 1980, the average UK house price was around £21,000 and mortgage costs accounted for 11.3% of disposable income.
Today, those figures are around £292,000 and 45.1% respectively.
Its research suggests the 6.43% mortgage rates of today are equivalent to a rate of 25.7% in 1980.