Some months, however, when she doesn’t have enough baby-sitting jobs lined up, Ms. McCarty has to make that “horrible phone call” to her parents to tell them that she can’t make her rent.

LOUISE GASSMAN, 28, has a rotating schedule of multiple jobs: as an actress; as an assistant to dance instructors at the Circle in the Square and Juilliard schools; as a baby-sitter; and in a variety of administrative roles and as a spinning instructor at SoulCycle, an indoor cycling studio in New York.

Ms. Gassman’s monthly income, which can vary greatly depending on whether she books an acting job, ranges from $1,800 to $4,000. Some months, almost all of her income goes to the $1,450 rent on her 290-square-foot studio on the Upper West Side of Manhattan. Whatever is left after essentials goes toward paying off her remaining $16,000 in college loans.

“I worry about money all the time,” Ms. Gassman said. “I live on a really tight budget, and I live paycheck to paycheck.”

Periodically, the accountant who cuts her check at SoulCycle reminds her that someone her age should be putting away $300 a paycheck for retirement, an amount that is sometimes almost half of her pay. “I’m like, retirement?” she asks. “Then I have the ‘Oh my God, Oh my God’ feelings.”

Ms. Gassman has come up with creative ways to save money. She has a policy not to spend $5 bills and instead puts them in a Tupperware container. So far, she’s been able to use this cash to pay for a new air-conditioner, for three plane tickets, and for her dog to be neutered.

Mia Branco, 23, says she is always worried about money, even though she also works four jobs. She is the house manager at the Discovery Theater at the Smithsonian Institute in Washington, teaches drama and music at Imagination Stage in Bethesda, Md., supervises the box office at the Woolly Mammoth Theater Company and works as a nanny.