Millennial homeownership has been off to a slow start. Roughly 1 in 3 millennials under the age of 35 own a home as of the end of 2018, according to the U.S. Census Bureau. That's 8 to 9 percentage points lower than previous generations' homeownership rates at ages 25 to 34, according to research from the Urban Institute's Housing Finance Policy Center. Yet many of the younger people lucky enough to own a place still suffer from buyer's remorse. Nearly two-thirds, or 63 percent, of millennials (ages 23 to 38) say they have regrets about purchasing their current home, according to a new poll of about 1,500 homeowners from Bankrate. Only 35 percent of baby boomers (ages 55 to 73) say the same, while about 50 percent of Gen Xers (ages 39-54) cop to some remorse.

The top reason millennials have regrets

Underestimating the hidden costs associated with buying and owning a home, including the ongoing responsibilities of maintaining it, is the No. 1 millennial homeowner frustration. It's a common mistake, experts say, and it can be a costly one. You need to know that you can truly afford to both buy and own a home, and to get the full picture, you need to do more than simply compare your current rent payment with the potential mortgage payment, Daryl Fairweather, chief economist at real estate site Redfin, tells CNBC Make It. "Do a full check of all finances," Fairweather says. "A lot of hidden fees come with owning a home that you might not consider immediately." That includes the insurance, property taxes and closing costs — which can be 2 to 5 percent of the home price. Those kinds of hidden costs even tripped up real estate mogul Barbara Corcoran early on. "When I bought my first home I showed up at the table to close without the closing costs," she told CNBC Make It. "Thank God I was able to borrow it from the very nice seller or I couldn't have closed on the place."

First-time buyers also often overlook the costs of upkeep and repairs. HGTV recommends buyers plan to spend 1 to 3 percent of the home's purchase price on annual maintenance. So if the home is priced at $300,000, your budget for this should be at least $3,000 each year. It doesn't help that cash-strapped millennials often struggle to afford just the down payment: Roughly 1 in 3 millennial homebuyers took on a second job to save up for it. "When paying for things like mortgages and student loans, [millennials] don't have much money to save for the hidden costs of owning a home," Fairweather says. The key to avoid regrets in the long run is to play it safe at the outset, Lawrence Yun, chief economist of the National Association of Realtors, tells CNBC Make It: "Start with a starter home and later trade up, rather than going for a 'dream home' on the first try."

There's a 'shortage' of starter homes

Unfortunately, though, many millennial homeowners end up paying more than they wanted to or had budgeted for because there aren't many homes available at the prices young people can comfortably pay. "Millennials have seen their rents go up year after year, and may think that buying a home is more affordable, but the fact of the matter is housing has become unaffordable across the board," Fairweather says. In many cities around the U.S., particularly in coastal areas, home prices are out of reach. Only 67 percent of homes available in 2018 located in metro areas tracked by Redfin were priced affordably for millennials — down from 71 percent of homes in 2017. In Los Angeles, only 19 percent of homes are in a price range that millennials can afford, based on their median incomes. "We need more affordable-priced homes, and the shortage of these properties are forcing people to possibly over-stretch their budget," Yun says.

Housing has become unaffordable across the board. Daryl Fairweather chief economist at real estate site Redfin

Other millennial regrets