Circuit Limits & Trading Halts
The guardrails that stop a stock from moving too far too fast in a single day.
To prevent panic and manipulation, exchanges cap how far a stock (or indexA basket of stocks tracked together to represent a market.) can move in one day. Hit the ceiling and it’s “upper circuitAn automatic trading halt when prices move too far.”; hit the floor and it’s “lower circuitAn automatic trading halt when prices move too far..” Trading in that direction then pauses or freezes.
IndexA basket of stocks tracked together to represent a market.-level circuit breakers (e.g. on a 10%/15%/20% NiftyA basket of stocks tracked together to represent a market. move) can halt the entire market briefly — a rare, dramatic safety valve seen in events like March 2020.
Why couldn’t I sell a stock stuck at lower circuit?
At lower circuit everyone wants to sell and there are no buyers, so orders queue unfilled. This is the danger of illiquid, circuit-prone small-caps — you can be trapped as the price falls in steps with no exit.