There is no one answer to this question as startup failure rates can vary greatly depending on a number of factors, such as the industry, the size of the company, and the stage of development. However, a recent study by researchers at Stanford University found that the average failure rate for Y Combinator startups is around 50%.
While this may seem like a high number, it's important to keep in mind that the majority of startups fail regardless of where they are incubated. In fact, according to the same study, the failure rate for non-Y Combinator startups is even higher, at around 60%. So while the failure rate for Y Combinator startups is certainly not ideal, it's still better than the average.
There are a number of reasons why startups fail, but some of the most common include lack of market demand, poor execution, and running out of money. However, it's important to remember that even the most successful startups face challenges and setbacks; the key is to learn from your mistakes and continue moving forward.