How much of a stock decline is normal in a year, and when should I worry?

Volatility is the price of admission, not a malfunction. Historically the U.S. stock market experiences an intra-year drop of around 10-15% in most years, even in years that finish positive. Corrections of 10% happen roughly once a year on average, and steeper bear markets of 20%-plus occur every handful of years. None of these are unusual.

So a routine 10-15% dip is not a reason to worry, it's expected. What warrants attention is not the size of the drop but whether your financial plan still works: do you have an emergency fund so you won't be forced to sell, and is your allocation one you can hold? If a normal decline threatens your ability to pay bills, the fix is more cash reserves and a tamer allocation, not market-timing. The market's long-term uptrend is built on surviving these regular declines.