How much money do U.S. families need to get by?

How much money do Americans need to maintain a modest standard of living, where families don't struggle to put food on the table or pay the rent?

In most large U.S. cities, meeting that basic level of economic security requires income that's far beyond the federal poverty line, which is often used to measure what families need to survive, according to a new study from the left-leaning Economic Policy Institute.

Indeed, the federal poverty line is increasingly outdated, no longer accurately marking the boundary between between getting by and financial hardship, according to EPI senior economist Elise Gould, one of the researchers who worked on the project to assess what families today need to meet a modest standard of living. The poverty threshold fails to take into account geographical differences, such as the higher rents in cities such as San Francisco, and also hasn't kept up with the rising cost of health care, among other issues, Gould contends.

Take the federal poverty cutoff for a family of four, which stood at $23,850 last year. That income level is about half of what a family of four would need to get by in the country's least expensive metropolitan area -- Morristown, Tennessee. The researchers estimate that a two-parent, two-child family in the town of roughly 30,000 would require gross income of $49,114 simply to cover rent, taxes, food, transportation, child care and other basics.

For families of four living in the 10 largest family budget areas (see chart below), the U.S. median household income of $53,046 would fall short in every location, EPI found. The most expensive city, not surprisingly, is New York, where a family of four needs $98,722 to afford their basic needs. The median household income in the Big Apple stands at only $58,003.

"Getting by" doesn't necessarily mean a middle-class lifestyle. The EPI's calculations assume that a family will simply have enough income to cover their bills, but there's no extra fat in the budgets that would allow for vacations or even putting aside money for an emergency. Given the gap between the country's median income and the EPI's budget estimates, it's no surprise that almost half of Americans don't have the resources to cover a $400 emergency expense.

"What we're thinking about is a secure but modest life; it's not actually a middle-class lifestyle," Gould said. A middle-class income would provide for "the ability to be more forward-looking -- to be able to save for your children's college, and being able to save for retirement, aside from just Social Security contributions, being able to have a little in the bank in case a rainy day comes up. This is not these families."

The discussion of what households require to afford the basics comes at a tough time for many Americans, given that real wages have been treading water for decades. Adjusted for inflation, the average U.S. hourly wage peaked in 1973, according to Pew Research. In the meantime, costs for everything from health care to housing have surged.

Among those costs is the price of child care, which the EPI found represents a significant portion of families' budgets in most U.S. cities. In fact, child care costs are higher than rent in 500 out of the 618 metropolitan areas included in the study. That result was "really striking," Gould said.

"Families can meet their budgets in other ways," such as by relying on family members and friends to provide child care, she noted.

The findings suggest the increasing need for child care reform, especially given the importance of early childhood education and the financial strain felt by many families, Gould says. In some states, the cost of child care is higher than the annual tuition at a public university, and both mothers and fathers have said they've given up work opportunities, quit or switched jobs to cope.