They’re millennials, Gen Xers and baby boomers. They work in big cities and rural towns. They’ve tried to save — but rent, child care, student loans and medical bills get in the way.

National data on the paycheck-to-paycheck experience is flimsy, but a recent report from the Federal Reserve spotlights the prevalence of extra-tight budgets: Four in 10 adults say they couldn’t produce $400 in an emergency without sliding into debt or selling something, according to the 2017 figures.

The partial government shutdown, which began last Friday and is temporarily halting pay for some 800,000 federal workers, has touched off a heated discussion on Twitter about what it means to get by in the United States. (President Trump warned this closure could “last a very long time” if Congress doesn’t meet his demands for billions of dollars for a border wall.)

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Even brief income lapses can spell disaster for some households.

“My husband is a Park Ranger in the Great Smoky Mountains National Park, and he had to sign his furlough papers,” one woman tweeted. ”We have a 4 yr. old and a 4-month-old, and we don’t know when his next check will come. Mortgage is due, Christmas 2 days away.”

“Broke my lease to accept new fed job for which I have to attend 7 months of training in another state,” another Twitter user said. (He later deleted the tweet). “Training canceled with shutdown. Homeless. Can’t afford short(?)-term housing/have to work full-time for no pay/returning Christmas presents.”

These and other #ShutdownStories took off online after U.S. Rep. Scott Perry (R-Pa.) suggested last week that a gap in wages wouldn’t be so bad.

“Who’s living that they’re not going to make it to the next paycheck?” he asked reporters, adding that most of those impacted would qualify for back pay.

According to economists: A lot of people.

“It’s astronomical what people need just to make it month to month,” said Heidi Shierholz, a former chief economist at the Department of Labor who now studies how middle-class families spend their wages at the Economic Policy Institute, a Washington think tank that is funded by foundations and unions. “Given the high cost of transportation, housing, health care … There is often no wiggle room."

About 2,000 custodians, security guards, housekeepers and other federal building workers are losing money this holiday season because of the shutdown, according to 32BJ SEIU, an East Coast labor union — and because such staffers are employed by contractors, they won’t be eligible for makeup checks.

“My supervisor told me we won’t be getting paid,” one State Department cleaner told The Post last week, “so my bills won’t be getting paid.”

Beyond the federal labor sphere, workers across a variety of professions struggle to make ends meet.

Sol Smith, chair of liberal arts at a Southern California college, said he landed his job after earning three degrees. But with four daughters and mounting health care costs, he said, saving just isn’t possible.

“I see no way out,” he wrote in an email to The Post. “I am 40, have built a strong career, have 17 years experience, and if something were to happen to me, my wife and kids would be homeless within a year when my life insurance ran out.”

Lani Harrison, 43, said she and her software engineer husband have trouble buying groceries after paying the $2,249 rent on their two-bedroom Los Angeles apartment. They’re raising three young kids and rely on her husband’s income, she said. Her work as a certified car seat installer earns her $40 per appointment, but the work isn’t steady.

“Each month, we have to stretch his paycheck to make things work,” she said. “We really don’t have any savings. Many months we go under.”

Sometimes, she confides in trusted friends.

“I’m often surprised that their stories are so similar to ours,” she said.

Dillon Holt, a housekeeping assistant at a Nashville hotel, said he’s down to one piece of chicken in his freezer. His checking account often hovers around zero, and he is unable to put away any money for the future or an emergency.

“I make $12.50, work 40-50 hours a week,” he said. “I still don’t have a savings account.”

Emily Webb, 38, said she works full time as an arts administrator in Columbus, Ohio, and waits tables on the side. Staying afloat each month, she said, is a precarious dance.

“It’s a scramble at the end of a paycheck to deposit my tips and make sure none of my automatic payments bounce,” said Webb, who has master’s degree but cannot make her student loan payments.

She’s grateful to work in her field, though, and loves her job. One big financial boost, she said, awaits her at the end of 2019.