It's been an interesting year in the stock market, to say the least. After plunging into a bear market at a record-breaking speed as the COVID-19 outbreak began, the S&P 500 has rebounded and then some. It's sitting at a gain of 16% with just a few days left in 2020.

However, many stocks have performed far better, and that's especially true in the financial technology, or fintech space. Here are three in particular that have doubled investors' money or more in 2020, but that are still attractive as we head into 2021.

Man in suit extending handful of money.

Image source: Getty Images.

3 Fintech stocks that doubled investors' money (or more)

I won't keep you in suspense. Here are three fintech stocks that have delivered total returns of 100% (or, in some cases, much more) over the past year.

Company (Symbol)

1-Year Total Return

Square (NYSE:SQ)

244%

PayPal (NASDAQ:PYPL)

116%

eXp World Holdings (NASDAQ:EXPI)

520%

Data source: YCharts. Total returns for 1 year ending Dec. 29, 2020.

A look at each company's performance explains why these stocks have performed so well.

In Square's case, its core payment processing business continued to perform well. The early success of its Online Store omnichannel platform is also encouraging. However, the real story is Square's Cash App, which has doubled its user base over the past year. Plus, the company has done a fantastic job of monetizing the platform with features like stock trading and cryptocurrency exchange. 

PayPal is in a similar situation. The online payments leader anticipates adding 70 million net new active accounts for 2020, doubling the initial expectations. The company now has nearly $1 trillion of annualized payment volume flowing through its platforms, including Venmo, which now has 65 million active users and a 61% year-over-year payment volume growth rate.

Last but certainly not least, disruptive real estate brokerage eXp World Holdings has more than 35,000 agents on its platform. It's growing at a remarkable pace. Over the past year, the number of agents and brokers on eXp's platform grew by more than 56% and the residential transaction volume closed by its agents increased by 112% to $23.6 billion. As a result, eXp's revenue and gross profit doubled year-over-year in the third quarter, and its cash flow nearly tripled.

Are these still good fintech stocks to buy now?

It's only natural to wonder if a stock is still a good value after performances like these. In all three cases, there could still be tremendous upside potential from here.

Square and PayPal still have tons of potential to grow their core payment processing businesses. The pair currently processes about $100 billion and $1 trillion in annualized payment volume, respectively, but this is quite small compared with the $185 trillion global payments market. Plus, Square is still in the relatively early stages of monetizing its Cash App, and PayPal has barely tapped into the revenue-generating potential of its massive Venmo platform.

While eXp's growth is certainly impressive, and more than $90 billion in annualized transaction volume may sound like a huge amount (and it is), it is still a relatively small fraction of the roughly $2 trillion of annual real estate transactions in the U.S. eXp operates in Canada, the U.K, Australia, and South Africa as well, so its addressable market is considerably larger.

The bottom line is that these companies have emerged as big fintech winners in 2020, but there's no reason to believe they won't keep winning. All three are entering 2021 with incredible momentum and could still be smart additions to long-term investors' portfolios now.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.