In Louisville, Ky., hundreds of residents are timebanking - instead of paying with money, they are paying with their time.

One recent morning, Laura McGarity baby-sat Frankie Underwood, 1, for three hours for free.

"I watch people's kids and they help me and it's been fabulous," McGarity said.

Across town, Becky LeCron, a professional photographer, took Gwen Kelly's family portrait, also for free.

"I saved at least $250," Kelly told ABC News.

Timebanking is booming, according to national group statistics, and can be found in 42 states.

In three years, the number of time banks across the country has nearly doubled to 569 - from Kent, Ohio, and Allentown, Pa., to Los Angeles. There are more than 37,600 total members.

The largest time bank in the US - the Visiting Nurse Service of New York Timebank - is in New York City with more than 3,200 members.

RELATED: Timebanking takes off.

Economists told ABC News it's a great idea and creates a sense of community.

Timebanking is organized through TimeBank USA, a national group founded by Edgar Cahn that helps communities get started and track their time.

The practice is like bartering, in which two people trade goods or services, but with time banks there is a pay-it-forward component.

With "time dollars," residents can get their oil changed, help with medical services, have their computer fixed or bike repaired, even take a yoga class.

RELATED: Pay it forward with a time bank.

At Jodie Tingle-Willis ' yoga studio in Louisville, which photographer LeCron attends, Dan DeSpain replaced the door frame.

In exchange for his time, Beth Thorpe gave him a ride to run errands because the brakes on his car needed replacing.

Linda Erzinger said she used her time dollars to visit chiropractor Dr. Rodrick Hahn - it's medical care Erzinger said she'd otherwise not be able to afford.

Last year, she saved $6,805, using time dollars to pay for plumbing, pet sitting, chiropractic adjustments, and help setting up her small business.

In exchange, she painted a mural in Frankie's nursery.

"I feel wealthy since I've been in the time bank - and I don't have cash," Erzinger said.

ABC News