The site also provides a way to dispute credit score errors — something that could save millennials lots of money on interest payments when applying for loans their scores qualify them for.

Bankrate, for its part, offers all sorts of financial advice, as well as analysis of bank interest rates, mortgages, credit cards, insurance and other products and services. Its most recent Bankrate Money Pulse survey finds that millennials are slower to invest in stocks than other age groups; while 54% of Americans don't invest, only a third of millennials do. And only 18% of those between 18 and 25 are investing.

But is this because they're financially ignorant of the potential stocks offer, or because they don't have the money? Millennial survey respondents cited the latter as the reason, with 46% giving that as their reason. However, the second most-cited reason was not knowing enough about stocks.

There's a possibility that a third reason has a lot to do with their abstention from investing, of course — a distrust of the stock market, especially after seeing what it did to parents and grandparents during the Great Recession. In fact, a study last year from Northwestern Mutual found that they were old souls when it came to money, quite conservative and risk-averse.

Some of the Credit Karma data bear this out. Among the 38 percent of millennials who said they have not taken out credit cards, Credit Karma found that 48% cited an aversion to debt as their top reason.