What Is a Price Limit?
Price limit is a boundary set by an exchange on how far a contract's price may move in a single session, beyond which trading halts or is restricted. It is imposed by the venue rather than chosen by a trader, and reaching it stops the trading rather than stopping the move.
Two terms in this area sound the same and are unrelated. A limit price is yours; a price limit belongs to the exchange, and it is the one that can trap you.
How it works
The exchange sets a maximum move for the session, usually a fixed amount or percentage from the previous settlement, applying above and below.
Nobody chose it and nobody can opt out. It is a rule of the venue, applying identically to every participant in that contract.
Reaching the upper band is “limit up”; the lower is “limit down.” Depending on the contract, trading either stops entirely or may continue only at or inside the band.
The part that matters
A halted market is a market you cannot leave. Your position stays open, its loss keeps accruing against the true value, and no order of any type will execute.
The next session opens with a reset band — often a wider one — and if the underlying reason has not changed, the contract can go limit down again immediately.
Consecutive limit moves are the scenario that ruins people. Not one large loss, but several sessions of accumulating loss with no exit available in any of them.
A worked example
A contract settles at 100 with a 7% daily band. The session’s floor is 93.
Overnight news makes the contract worth 80. It opens, sellers pile in, and it trades to 93, where it locks. There are no buyers at 93 because the thing is worth 80.
A holder with a stop at 95 is filled around 93 if they were early, and not filled at all if they were not — because after the lock there are no trades for a stop to trigger into.
The next session’s band starts from 93. Another 7% takes it to 86.5, and it locks again. The true price of 80 is not reached until the third session, and the holder has been unable to act throughout.
Why exchanges impose them
To stop a cascade. A violent move triggers margin calls, which force selling, which moves the price further, which triggers more margin calls. A pause breaks the loop mechanically.
To buy time for information. Many extreme moves are driven by something that turns out to be wrong. A halt lets participants read the actual news rather than react to the tape.
To let margin be posted. A clearing house needs its members solvent, and a pause gives them hours to find the cash rather than minutes.
And because the alternative has been tried. Markets without any circuit-breaking mechanism have produced disorderly collapses where the price found no level at all, and the rules exist as a response to specific historical events rather than as theory.
The original data
On this site’s shared series the median bar range is 0.493, the ninetieth percentile 1.101 and the largest single bar 2.338 — the largest bar being 4.7 times the median.
A band set around a typical bar would halt trading constantly. A band set near the largest observed move halts almost never, and only when something genuinely unusual is happening, which is the design intent.
And the drawdown measurement gives the scale of a normal bad stretch: 95% of bars sit below a prior peak, maximum decline 3.76%, longest stretch 73 bars. A price limit is not designed for that; it is designed for the event outside everything that series contains.
What it does to the instruments around it
Options on a locked contract stop being hedgeable. The underlying cannot be traded, so anybody delta-hedging is frozen with whatever exposure they had at the moment of the lock.
Related markets carry the flow instead. If one contract is locked and a correlated one is not, the pressure moves there, and that second market can behave strangely for reasons that have nothing to do with it.
And the liquidity picture inverts. The band is reached precisely when everyone wants to trade, so the rule removes the market at the moment of maximum demand for it — which is the trade-off the exchange has consciously accepted.
None of that is an argument against the rule. It is an argument for knowing the band exists on any contract you hold, and for sizing a position so that being unable to exit for two sessions is survivable.
When it fails
The characteristic failure is a stop order that never triggers. The holder has a stop at a sensible level, the market gaps past it and locks limit down, and no trade prints at the stop level — so the stop sits unexecuted while the position bleeds. The protection was structured around the assumption that a market exists to sell into, and the band removed that market at exactly the moment the assumption mattered. The order was correct and the assumption behind it was not.
A second failure is confusing it with a limit price, which is the trader’s own instruction and does something entirely different.
A third is assuming the lock means the price has stopped. It has not — only the trading has, and the gap between the locked price and the real one is the loss still coming.
A fourth is holding leveraged positions in limit-prone contracts without sizing for consecutive locked sessions.
And a fifth is treating the reopening price as a fresh start. It is the continuation of a move that was interrupted, and the band resets to allow the same distance again.
Related
Limit price covers the trader’s own instruction with the confusingly similar name. Market order covers the instruction that cannot execute in a locked market. And liquidity covers what disappears at the band.
The most dangerous thing about a price limit is that it looks like protection. It stops the screen moving. It does not stop your loss growing, and it removes the one thing you needed at that moment, which was the ability to get out.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.