Market-wide circuit breakers — this is where the 20% lives. Based on the S&P 500 vs. the prior close: down 7% is a Level 1 halt (15 minutes), down 13% is Level 2 (another 15 minutes), down 20% is Level 3 and the whole market closes for the rest of the day. Levels 1 and 2 only trigger before 3:25 PM ET; Level 3 ends the day whenever it hits. March 2020 tripped Level 1 four times in two weeks. Level 3 has never fired.

Individual stocks — no daily cap at all. What exists is LULD (Limit Up-Limit Down): rolling price bands of 5% for big names, 10% for most everything else, ~20% for cheap stocks, doubled near the open and close. If the price sits at the band edge for 15 seconds, you get a 5-minute volatility halt. Then it reopens and can keep dumping. That’s why a blown earnings print can take a stock down 60% in a session with eight halts on the tape — the halts slow the bleed, they don’t cap it.

Countries like China and Korea do have hard daily limits on single stocks (±10%, ±30%). The US doesn’t. Which is also why single-stock 2x ETFs are spicy — the underlying gaps down 50% and the fund is functionally toast.