What it means
A market works smoothly when buyers and sellers arrive in similar numbers at similar prices. If there are far more buyers than sellers, there is not enough stock on offer and the price tends to rise.
If sellers dominate, the price tends to fall. Imbalances are most visible during opening and closing auctions, where orders are collected and matched at a single price.
Exchanges publish the size of the imbalance and the indicative price, which is the price at which the most shares would trade. Traders can then add orders on the other side, and this helps the final price reflect real supply and demand.
Large imbalances can also lead to a trading halt. If an exchange sees a sudden gap between buy and sell orders in a share, it may pause trading for a short time so that the market can absorb the information.
This protects investors from wild price swings caused by a temporary shortage of orders. For a finance professional, the point is that an imbalance is a signal.
A big buy imbalance before the close may suggest that a price will end higher than it would otherwise, while an unexpected sell imbalance might signal bad news or forced selling by a fund. It is not a guarantee, so it should be used as one input.
Companies that run share buyback programmes or execute large orders pay attention to this, because adding to an imbalance on the wrong side can push the price against them. Spreading orders over the day is a common way to avoid this.
Smaller investors rarely trade in auctions, but they still feel the effects. A closing price that is pushed by an imbalance becomes the reference for fund valuations, margin calls and index levels, so it is worth knowing how it came about.
In practice
Real-world examples.
Example
A large pension fund needs to buy shares in a utility company on the last day of the month. It notices that the closing auction already shows a large buy imbalance. The fund places part of its order earlier in the day to avoid paying a higher closing price.
Example
An exchange publishes a sell imbalance in a mid-sized retailer minutes before the opening auction. A trader adds buy orders at a slightly lower price and picks up shares at a discount. The extra orders help the opening price settle closer to fair value.
Example
A news report about a product recall leads to a sudden flood of sell orders for a food company. The exchange pauses trading briefly, publishes the imbalance and reopens with an auction. Prices adjust in an orderly way, and the stock opens only slightly below its earlier close, about 3% lower, rather than collapsing.
Formula
Calculation
Order imbalance = Buy order volume - Sell order volume
Imbalance ratio = Order imbalance / Total order volume
Suppose that in a closing auction for a share there are buy orders for 120,000 shares and sell orders for 80,000 shares. The order imbalance is 120,000 - 80,000 = 40,000 shares in favour of buyers.
Total order volume is 120,000 + 80,000 = 200,000 shares, so the imbalance ratio is 40,000 / 200,000 = 20%. If the indicative price is $50.00, the 40,000 excess shares represent 40,000 x $50.00 = $2,000,000 of unmatched buying interest.Case study
Seen in the real world.
Meridian Asset Partners is a fictional fund manager that needed to sell 500,000 shares of a technology company by the end of a quarter. The shares normally trade about 2,000,000 a day.
The trading desk saw that the closing auction was already heavy with sell orders. Adding another large sell order would deepen the imbalance and push the closing price down.
In this illustrative case the desk sold 300,000 shares gradually through the day and the final 200,000 in the auction after checking the published imbalance. The average price was better than a single large sale at the close would have achieved. The desk recorded the result so that it could review its approach next quarter.
Watch out
Common mistakes.
- Assuming every imbalance signals bad news, when many arise simply from index funds rebalancing at the close.
- Placing a large order into an auction that already has a one-sided imbalance without checking the published figures.
- Believing imbalance information guarantees where the price will end, when it only indicates current supply and demand.
Questions
People also ask.
Why do imbalances happen mostly at the open and close?
Because many orders are collected and matched at one time, and investors who cannot trade during the day tend to submit orders for these auctions.
Who publishes imbalance data?
Exchanges usually publish it during the auction period, and many trading platforms display it.
Can an imbalance cause a trading halt?
Yes. If the gap between buyers and sellers is very large, an exchange may pause trading to allow orders to rebalance.
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