What Is a Block Deal? Why Large Stakes Trade Off-Market at a Discount

What a Block Deal Actually Is

Imagine a major shareholder suddenly needs to sell 5% or 10% of a company's shares in one shot. If that entire order hit the regular buy-side order book at once, what would happen? The book only holds so much resting demand at any given price, and a sell order that size would chew through it level by level, dragging the price down in the process. To avoid that, a large stake is instead handed off in a single transaction to a pre-arranged buyer (or group of buyers), before the market opens or after it closes rather than during regular trading hours. This is what's known as a block deal (also called a block trade). On the Korea Exchange it's formally categorized as an off-hours large-volume trade; the defining feature everywhere is that the price and quantity are negotiated in advance, off the public order book, so the transaction doesn't move the live market price when it prints.

Why Not Just Sell It on the Open Market?

As covered in Market Microstructure Basics, the regular order book is a finite stack of resting orders spread across multiple price levels. A sell order large enough to represent a meaningful share of a stock's typical daily volume will eat through the nearest bids first, then the next tier down, and so on — pushing the average execution price noticeably lower as it goes. This is called market impact cost, and it creates an ugly paradox for the seller: their own selling pressure drags down the price at which the rest of their own shares get filled. A block deal sidesteps this entirely by never touching the public book. Seller and buyer agree on price and quantity privately, then execute at a moment — typically just before the opening auction or just after the closing print — chosen specifically so it doesn't disturb the regular market price.

How the Price Gets Set — the Discount to the Closing Price

A block deal's execution price is typically set as a discount to the prior day's or same-day's closing price. Why does a discount exist at all? From the buyer's side, this trade requires absorbing a large position all at once, unlike accumulating shares gradually on the open market. A bigger position also means more market impact whenever the buyer eventually needs to sell it back, and buyers demand compensation — a lower entry price — for taking on that risk. Sellers, in turn, weigh the discount against the market impact cost they'd otherwise eat trying to unload the same shares gradually through the regular book, and often conclude the discount is the cheaper cost to bear.

The size of that discount depends on the deal's size, the stock's typical liquidity, how urgently the seller needs to close the sale, and prevailing market conditions. A commonly cited rule of thumb in the industry puts the discount somewhere around 2% to 8% off the closing price — this is an informal market convention, not a fixed formula. For a thinly traded small-cap stock, or an unusually large block, the discount can stretch past 10% simply because there are fewer natural buyers to compete for the shares. When institutional demand is strong and multiple buyers compete for the same block, the discount can shrink to under 2%.

Two Ways a Block Deal Gets Done

Block deals generally run through one of two structures. The first is accelerated bookbuilding: the seller (or the bank running the process on their behalf) canvasses a list of institutional investors within a matter of hours, collecting indications of "I'll buy this much at this price" until the order book is filled, then allocates the shares to whichever bidders offered the best terms. In this version, the bank acts purely as an intermediary and never takes the shares onto its own balance sheet.

The second is a bought deal, where the investment bank itself buys the entire block from the seller at an agreed price first, then resells it to a range of investors afterward. Because the bank is now carrying the position — and the risk of reselling it — on its own balance sheet until it finds buyers, it typically demands a steeper discount to compensate for that exposure. For the seller, the appeal is certainty: cash in hand immediately, without needing to line up buyers first.

A Worked Example

Suppose a major shareholder of Company A wants to sell 10 million shares through a block deal, and the previous day's closing price was ₩10,000. After negotiation, a group of institutional buyers agrees to take the shares at a 5% discount — ₩9,500 — and the seller raises a total of ₩95 billion (10 million shares × ₩9,500). If the same shareholder had instead tried to sell that volume through the regular market, the sheer size of the order relative to typical daily trading volume could plausibly have pushed the execution price below ₩9,500 anyway. Seen this way, the 5% discount isn't simply a loss — it's closer to a fixed cost paid upfront in exchange for avoiding an uncertain, potentially larger decline and the time it would take to sell gradually.

Why the Market Often Treats Block Deals as Bad News

Block deal announcements frequently rattle a stock in the short term, for two overlapping reasons. First is a signaling effect: when the people who know the company best — founders, executives, major shareholders — sell a large stake at once, investors read it as evidence that insiders think now is a good time to sell. In reality, the motivation is often unrelated to the company's outlook: raising cash for inheritance or gift taxes, a private equity firm exiting an investment, or a pension fund rebalancing its portfolio are all common, fundamentals-neutral reasons. But absent a clear explanation, the market tends to assume the worse interpretation first.

Second is overhang concern, the same dynamic covered in IPO Lock-Up Periods and Overhang. As long as investors suspect the buyers who just picked up the block might turn around and sell once their own restrictions lift, the market treats that stake as a standing pool of potential future supply and discounts the stock accordingly.

These two effects tend to reinforce each other. Once the signaling effect has already put investors on edge, overhang concerns tend to resurface every time a lock-up expiration date approaches. That's why two block deals of identical size can generate very different market reactions depending on whether the seller's motive was clearly disclosed and how long a lock-up was attached to the buyer's new shares.

Who Actually Uses Block Deals, and When

Block deals show up on both sides of the market. On the sell side: founders raising cash for inheritance or gift taxes, private equity firms exiting a portfolio company, pension funds or asset managers trimming an oversized position, and parent companies monetizing part of a stake in a newly listed subsidiary. On the buy side, a strategic investor trying to build a large position quietly uses a block deal to avoid the classic problem of open-market buying — where the act of accumulating shares itself pushes the price up before the position is even complete.

Block Deal vs. Rights Offering vs. Open-Market Selling

Several methods exist for moving a large stake, and they differ in where the proceeds go and how share count is affected.

Method	Proceeds go to	Shares outstanding	Immediate market impact
Block deal	Existing shareholder (seller)	Unchanged — ownership of existing shares transfers	Low (negotiated off-book, then executed)
Rights offering	The company (issuer)	Increases — new shares issued	Dilution priced in for the new shares
Open-market bulk selling	Seller	Unchanged	High (works through the book level by level)

A block deal doesn't create new shares the way a rights offering does, so there's no dilution effect from an expanded share count. It also carries far less immediate price impact than dumping the same size order on the open market — though, as the signaling and overhang effects above show, that doesn't mean it has zero effect on the stock.

How Lock-Ups Cushion the Blow

To temper these concerns, block deal agreements typically include a lock-up provision preventing the buyer from reselling the shares for a set period — commonly cited ranges run from three months to a year, though every deal differs. This can be thought of as the buyer trading part of their discount for a commitment not to immediately flip the shares. A disclosed lock-up generally means the resale pressure will be spread out over time rather than hitting the market all at once, so it's worth checking both the discount and the lock-up terms — not just the discount alone — when a block deal is announced.

Key Takeaways

• A block deal moves a large stake off the public order book, executing before the market opens or after it closes with a price and quantity agreed in advance — avoiding the market impact cost of selling the same size on the regular book.
• The execution price is usually set at a discount to the closing price — commonly cited around 2% to 8%, though this varies with deal size, liquidity, and urgency.
• Deals run through either accelerated bookbuilding (bank as intermediary) or a bought deal (bank takes the position onto its own balance sheet first).
• The market often reads block deals negatively due to a combination of signaling effects and overhang concerns about future resale.
• A lock-up on the buyer's new shares reduces overhang risk, so it's worth checking for one alongside the discount when a block deal is announced.

Frequently Asked Questions

Is a block deal always bad news for the stock?

Not necessarily. Reasons like raising cash for inheritance taxes or a private equity exit are often unrelated to the company's actual outlook. But without a clear explanation, the market tends to interpret the sale negatively at first, which is why short-term volatility around block deal announcements is common.

Can retail investors participate in a block deal?

Rarely. Block deals are typically arranged with institutional investors within a short window because of the size of capital required, so retail investors usually only see the outcome — discount, size, and any lock-up terms — through a public disclosure after the deal closes.

Does a bigger discount mean worse news?

A larger discount can suggest the seller struggled to find buyers or needed to close the sale urgently, which is sometimes read as a more negative signal. That said, stocks with naturally low liquidity can carry a wider discount even under normal circumstances, so it's more accurate to compare the discount against that stock's usual trading characteristics than to judge it in isolation.

⚠️ This article is for informational and educational purposes only and does not recommend buying or selling any specific stock. The figures in the worked example are simplified hypothetical values used to illustrate the calculation, not real transaction data. Actual block deal discounts and terms vary by transaction.