It's a pretty well-known stat that I think originally came from one of Schwab's detailed Modern Wealth Index reports -- which are survey-based so there is likely some inaccuracy; they report 3% margin of error -- but other similar studies generally put the number somewhere between 53% and 63%.

From their methodology:

> The Modern Wealth Index, developed in partnership with Koski Research and the Schwab Center for Financial Research [...] was conducted by Koski Research from January 12 to January 19, 2018, among 1,000 Americans aged 21 to 75. Quotas were set so that the sample is as demographically representative as possible. The margin of error for the total survey sample is three percentage points.

Anecdotally, this percentage makes sense to me based on roughly half of the people in my circles/family/life living paycheck to paycheck, but there's obviously some exposure bias at work there too. It's possible you have some exposure bias as well if that number seems too high for you.