According to the American Chamber of Commerce, 61.6 million Americans are employed by small businesses – nearly half of the US workforce.

However, a study published on Tuesday by online financing platform Stenn shows that almost a quarter of these businesses are on precarious financial ground.

Over one in five small and medium-sized businesses (SMBs), or those with at least one and at most 500 employees, said they have only one to five months of cash reserves for emergencies.

That means, according to the study, one in five US small and medium-sized businesses could run out of cash by Christmas and are particularly “vulnerable to financial shocks”.

The study noted that 50% of SMBs fail in their first year and 45% fail within the first five years, and also that these businesses are essential: They are the nation's largest employer by category.

Related: We asked 500 small business owners what they thought about the economy, inflation and the upcoming election. Here are the results.

“Small businesses are the unsung heroes of the US economy,” said Stenn Chief Commercial Officer Noel Hillman.

In good news, most SMBs have more cash on hand—more than half (56.4%) or roughly three in five SMBs said they had six to 18 months of cash on hand.

Also, over four out of five businesses said they were months away from growing their businesses and increase in income. About 45% said scaling would take six to 18 months, while 36.8% said it would take only one to five months.

The survey was based on a sample of 250 founders, owners and CEOs who lead businesses with at least $2.5 million in annual revenue and one to 500 employees. It took place between August 29 and September 5.

Related: A small business owner's guide to managing funds and investments

Another survey released earlier this month by accounting software company QuickBooks bears this out 93% of consumersor about 240 million people, plan to shop at small businesses during the holidays.