Amid rising employment rates and stagnant wage growth, a growing number of full-time workers have added a little something to their resumes: a freelance job on the side.

That's according to new data from LinkedIn, which surveyed over 9,600 users on its new ProFinder platform (a pilot program that connects businesses with freelance workers). While the most likely users are avid, independent workers, they also serve as an indicator of where the gig economy is headed. Most professionals on ProFinder are full-time freelancers, but 20 percent are now listing freelancing services as a side gig to their full-time jobs.

Millennials are more likely to engage in part-time freelance work, the data shows. But it's important to note that men are more likely to be working a side gig. Nearly half of these workers (47 percent) live in states with the highest-cost-of-living cities in the country: California, Florida, Illinois, Massachusetts, New York, and Texas. The freelance industries include entertainment, financial services and insurance, professional service, staffing, and tech and software.

How much are side hustles helping these professionals make ends meet? At an average of $21 per hour, and between 10 to 15 hours of client work per week, part-time freelancers can earn up to an extra of $12,000 or more each year, according to a recent survey from cross-border payments platform Payoneer.