England's income tax of 1436 identified 2,184 laymen with incomes from land, annuities or office of 20 pounds or more. This was apparently something of an undercount, missing some households and underestimating some incomes.
With about 500 monastic houses with incomes of 20 pounds or more and 8-9,000 parishes, the number of prelates, church officials and holders of the richest benefices with equivalent effective incomes probably came to almost as many.
Some merchants and craftsmen would have incomes of 20 pounds or more from their business that would not have been subject to the 1436 tax. London's 25 alderman were taxed as the same rate as knights banneret in the 1379 poll tax, and in the 15th century they had an explicit property qualification of at least a thousand pounds, which, if all invested in trade might yield an income of at least a hundred pounds a year. If the merchants had a similar income distribution to the landowners, there could have been about 230 London merchants with incomes of 20 pounds a year or more. However, merchants also liked to invest in real estate, and 87 London merchants were assessed as having lands and rents of twenty pounds or more in 1436, so they would already have been counted in the laymen above, leaving 146 families with less or no real estate with incomes of 20 pounds or more.
Given London's preeminence in population and wealth, the total number throughout England might have been three times that, or about 450.
Allowing for some undercounting in the 1436 tax, that comes to a total of about 5,000 households, a bit more or less than 1%, depending on which estimate of England's population you choose.
Two things are striking about the results of this exercise. First, medieval England was a much poorer society than today's. 20 pounds supported the lifestyle of a landed squire, a fortunate estate
by contemporary standards, but not a lavish one by ours. Second, the primary sources of income for the wealthy were very different from today: inherited land, the church, and the law, with trade and manufacturing a relatively small part of the total.