Effect of Limit-Up/Down Price Change

Start here, because everything else in the unit builds on what a limit actually does. A price limit is a boundary on how far the price can travel that session, not an automatic shutdown. Anchor that first, then the expanded-limit, margin, and lock mechanics all follow.

The Daily Price Limit

The daily price limit is the rulebook boundary each exchange places on a contract's price move for a single session.

• Daily price limit: the maximum amount a futures price is allowed to move up or down from the prior session's settlement price during one trading session, fixed by the rules of the exchange.
• Settlement price: the exchange-determined official price at the close of a session. The daily limit is measured from this number, not from any intraday price. Yesterday's settlement is the anchor; today's limit sits a set distance above and below it.
• Trading continues at or within the limit: the limit caps how far the price can go, but buyers and sellers can keep transacting anywhere inside the daily range, and at the boundary itself. The limit is a fence around the day's price, not an off switch for the market.

Think of it this way: picture yesterday's settlement price as a stake driven into the ground, with a rope of fixed length tied to it. The price can wander anywhere the rope reaches, up or down, and trades happen freely inside that circle. What the price cannot do is stretch past where the rope ends. The exchange simply will not accept a trade beyond that point.

Exam Tip: Gotchas

• The limit is measured from the prior session's settlement price, not from the intraday high, low, or open. If a question anchors the limit to any price other than the previous settlement, it is wrong.
• Reaching a limit does not halt all trading. The price can still trade at the limit or anywhere within the daily range. Only trades beyond the boundary are blocked.

Limit Up vs. Limit Down

The two directions are mirror images: one caps how high the price can print, the other caps how low.

• Limit up: the price rises by the maximum amount permitted for the session and reaches the upper boundary. No trades may print above the limit-up price.
• Limit down: the price falls by the maximum amount permitted and reaches the lower boundary. No trades may print below the limit-down price.
• Limit move: a session in which the price advances or declines the full permissible amount. A contract that has reached its limit is said to be "at the limit."

Real-world example: say a grain contract settled yesterday at $5.10 per bushel and the daily limit is $0.10. If heavy selling drives the price down to the $5.00 limit-down level, a trader cannot sell at $4.99, because $4.99 is outside the daily limit. The only way to sell is to find another trader willing to buy at the $5.00 boundary. (These figures are illustrative; actual limits vary by contract and change over time, so do not memorize the numbers.)

Exam Tip: Gotchas

• Limit up blocks prints above the boundary; limit down blocks prints below it. A common trap flips the direction. Limit up is the ceiling on an advancing market; limit down is the floor on a declining one.

What a Limit Change Actually Does

The point students miss is that a limit acts on the printed trade, not on the underlying supply and demand.

• Caps the print, not the demand: buying or selling pressure can keep building, but the exchange will not accept a trade beyond the boundary. The pressure is still there, just unable to move the price further that session.
• Signals volatility: reaching a limit tells the market that the supply and demand imbalance is severe. That is exactly why exchanges respond with the expanded-limit and margin mechanics covered in the next two sections.

Exam Tip: Gotchas

• A limit caps the price, not the imbalance behind it. Demand or supply pressure does not vanish at the limit; it simply cannot push the printed price past the boundary until the next session's (usually wider) limit applies. When the imbalance is so one-sided that no counterparty will trade at the limit, the market becomes "locked," the special case covered later in this unit.