It’s obvious that the economy is white-hot and it can be measured in many ways. The unemployment rate is near historic lows. Small business optimism is at record highs. GDP growth is through the roof. And job creation continues to be strong.

But one indicator that might not immediately come to mind when thinking about the health of the economy is retirement savings—which for most Americans, is linked to the stock market. And fortunately, just as with all of the other economic indicators, retirement savings are skyrocketing.

According to new data from Fidelity Investments, the number of 401(k) millionaires has hit a record high. Over 165,000 people have Fidelity retirement accounts worth over $1 million–50,000 more people than the previous year. Not only does that mean more people will be able to retire comfortably, but it also signifies a broad increase in financial security, which leads to more spending and investment in the present—a trend that will further drive up economic growth. 

The economy is booming. And it can be proven in more ways than one.