What it means
The quoted market price reflects small trades between willing buyers and sellers on a given day. It tells you nothing about what would happen if someone pushed several months of normal trading volume into that same market in a single week.
The size of the discount depends mainly on how long it would take to sell the block without disturbing the price. Valuers estimate this by comparing the block to average daily volume and assuming the seller can only take a modest slice of each day's trading, often somewhere between 10% and 25%.
A block that needs a hundred trading days to clear justifies a far larger discount than one that clears in five. Blockage is not the same thing as a discount for lack of marketability, although the two are frequently confused.
Lack of marketability applies when there is no ready market at all, such as shares in a private company with no buyers waiting. Blockage applies when there is a market, but it is too thin to absorb your particular holding quickly.
In practice the discount is built from the cost of waiting plus the cost of pushing the price down. Typical blockage discounts in valuation work sit in a range of roughly 5% to 20%, with anything larger needing careful supporting analysis.
Because the figure involves judgement, it is one of the most frequently challenged inputs in a valuation dispute. There is a useful cross-check that valuers apply.
If a real block trade in the same stock has happened recently, the discount achieved in that deal is powerful evidence, and it usually carries more weight than any theoretical model. Absent such evidence, option pricing approaches are sometimes used to estimate the cost of the delay.
In practice
Real-world examples.
Example
An estate contains 1,500,000 shares in a thinly traded regional bank. The tax valuation applies an 11% blockage discount, reducing the reported value by several million dollars and cutting the estate tax bill accordingly, supported by a written liquidity analysis.
Example
A divorce settlement requires the value of one spouse's holding in a listed family company to be fixed. Because the stake represents nearly two years of normal trading volume, the court accepts a 15% blockage discount rather than the quoted market price.
Example
A charity receives a donated block of shares equal to forty days of average trading volume. Its finance team records the gift at a discounted value in the accounts and sells the position gradually over three months, which validates the discount used.
Formula
Calculation
Blockage discount amount = marketable value x discount percentage, where the discount reflects the days needed to liquidate the block.
An estate holds 2,000,000 shares in a small listed manufacturer quoted at $25.00, giving a marketable value of 2,000,000 x $25.00 = $50,000,000. The stock trades an average of 100,000 shares a day, and the valuer assumes a seller could take 20% of daily volume, or 20,000 shares a day. Clearing the block would therefore take 2,000,000 / 20,000 = 100 trading days, close to five months. The valuer applies a 12% blockage discount of $50,000,000 x 0.12 = $6,000,000, giving a reported value of $50,000,000 - $6,000,000 = $44,000,000, or $22.00 a share.Case study
Seen in the real world.
This example is fictional and purely illustrative. When the founder of Ashwood Ceramics died, her estate included 2,400,000 shares in the listed company she had built, quoted at $18.00 and therefore worth $43,200,000 at the screen price. The stock traded around 60,000 shares a day, meaning the estate held roughly forty days of total market volume.
The estate's valuer argued that a realistic seller taking 15% of daily volume, or 9,000 shares a day, would need 2,400,000 / 9,000 = 267 trading days to exit, more than a full year. Combining that delay with observed discounts on recent block trades in similar companies, the valuer proposed a 16% blockage discount of $43,200,000 x 0.16 = $6,912,000, giving a value of $36,288,000.
The tax authority initially argued for 6% but settled at 13% after reviewing the volume analysis, producing a discount of $5,616,000 and a final value of $37,584,000. The estate's advisers noted afterwards that the single most persuasive piece of evidence was not the model but a comparable block trade in a peer company that had priced at a 14% discount.
Watch out
Common mistakes.
- Confusing blockage with a discount for lack of marketability. Blockage assumes an active market that is simply too small for the block, while lack of marketability assumes there is no ready market at all.
- Applying blockage to any large holding automatically. If the stock is highly liquid and the block represents only a day or two of volume, no meaningful discount is justified.
- Ignoring that a control premium may point the other way. A very large stake can carry influence over the company, and that value can partly or wholly offset the blockage effect.
Questions
People also ask.
How large is a typical blockage discount?
Most supported discounts fall between 5% and 20%, driven mainly by the number of trading days needed to liquidate the position.
Do tax authorities accept blockage discounts?
They generally do in principle, but they scrutinise the supporting analysis closely and often negotiate the percentage down.
Can a blockage discount apply to bonds or other assets?
Yes, the same logic applies to any asset where the holding is large relative to normal trading, including corporate bonds and some property portfolios.
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