Most determinations of class in developed countries involve money. At between $50,000 and $150,000 US for a family of four, most individuals feel that they are solidly in the middle class. In a normal economy, this amount of money is expected to provide enough to own a home, to provide a level of dress, some dining out, recreation, a late model car, an annual vacation and paid health care, along with required and voluntary contributions to a retirement income.
But other factors that separate the upper middle from the middle class involve position, title, level of education and amount of independence from an employer. Still more factors involve the type of work done, whether it is labor, office, military or professional. The terms "blue collar",white collar" come to mind. There are salaried, hourly wage, and contract workers. There are management and non management, professional, skilled trade and labor workers.
The facts are that money is not sufficient to stratify society by class. A person who does hard labor, rarely visits an office and who rarely wears a suit and tie can earn double or even triple the salary or income of a person who is in management and who holds an impressive education and title. This is due to non management overtime, the rarity of skills involved and who it is that the individual is working for. A government civilian with a fairly low GS rating can make more than a top military leader when they have special skills, union contracts and have special assignments that pay extra for travel, temporary duty, hardship, overtime, premium time and so on.
The term "management" may even hold a stigma, since today's management career environment is so volatile. There is now less pride in the job and more fears of layoffs, along with the idea that the job can be a minefield of office and other politics. Many people who hold college and even advanced degrees and who are quite qualified for management jobs prefer to stay in the non management ranks which often hold less uncertainty and stress.
Entry level professionals, such as military officers, medical interns and residents and entry level PhD holders can earn far less than experienced nurses, support personnel, managers and others, and can have less power within an organization. The benefits for these individuals is that they will advance in power, position and title far more rapidly than other personnel. This makes having a professional credential a factor that moves the person into the upper middle classes more rapidly than would happen without the credentials.
With entry level professionals, it is quite possible that they come from the middle, upper middle and upper classes in the first place, making upbringing, unearned or inherited wealth and other factors a part of their educational and social makeup.
Being a business owner gives a certain social cachet. As a merchant, the possibilities of wealth are highly variable. But the merchant class can cover everyone, from the street vendor who quietly pulls in a hundred grand a year, to the owner of several profitable franchise stores, to an up and coming real estate developer.
Being a skilled trade person can place a person in the middle class or even upper class, while the person gets hands dirty, works in unglamorous places and engages in hard physical labor. Electricians, plumbers, masons, farmers, dairy owners and so on have special skills that are not that easy to obtain, are required by everyone, and that can result in more pay than a lot of other fields. The individuals might not have an extensive education in the sciences and classics and may prefer recreation and entertainment that others look down on, but they are solidly in positions that provide much more income and more opportunities for making income.
In the end, if money is the only determinant, than the middle class is either defined as having an income that lies exactly in the middle, between the lowest and highest incomes. Or, there is a monetary cutoff that might be between 40,000 and 80,00 for the middle class and 80,000 and up for the upper middle class.
But, there is "income" and there is "net", or "disposable" income, which can be vastly different. After taxes of various sorts, there are the costs of being employed or of owning a business.
If credential and title are involved, then an advanced college degree, a substantial position or title, the type of work and a higher income defines the upper middle classes. In addition, speech quality, socializing, personal style and habits, entertainment preferences, social connections, memberships in organizations is a factor. A person can have worked their way up, observing and taking on affects of the upper classes or a person can come from the upper classes and have the affect of an "average joe".
As a result, in society the concepts of "middle and upper middle class" are as much a matter of personal judgment and perception as they are a matter of income. Officially, the stratification is based on income, but in these volatile economic times, especially where the unanticipated costs of health care and housing are involved, income may not be a reliable indicator of a person's potential to make their way up or down the social ladder.