Circuit breakers are the rules that stop trading when prices move too far, too fast. US stock markets have two main layers. Market-wide circuit breakers halt every stock and options exchange when the S&P 500 falls 7%, 13% or 20% in a day. Limit Up-Limit Down (LULD) bands work one stock at a time, pausing trading for five minutes when a single name breaks out of its allowed price range. On top of those sit ordinary trading halts that exchanges call for news, plus a short-sale restriction that kicks in after a 10% drop.

The rule that has defined active retail trading for a quarter century is gone. On April 20, 2026, FINRA published Regulatory Notice 26-10, adopting new intraday margin standards under Rule 4210 that replace the day trading margin framework in its entirety — including the pattern day trader designation and the $25,000 minimum equity requirement that came with it. The changes took effect June 4, 2026, with brokers permitted an 18-month phase-in through October 20, 2027.

The Cboe Volatility Index is the most quoted and least understood number in financial markets. It is cited daily as the market’s “fear gauge,” yet most of the commentary surrounding it treats the index as a sentiment poll rather than what it actually is: a precise, formula-driven measurement of the price of insurance on the S&P 500. Understanding the distinction is the difference between using the VIX as a tool and being used by it.