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Key Takeaways
- An odd lot is smaller than the stock’s effective round-lot size.
- The four Regulation NMS round-lot sizes are 100, 40, 10 and 1 share.
- With a 40-share round lot, 25 shares is odd, 80 is two full lots and 95 is mixed.
- The 95-share mixed lot contains 80 full-lot shares and a 15-share remainder.
- Combine share quantity, quote price and completed executions when reviewing liquidity.
What is an odd lot?
An odd lot is a stock order, quote or trade quantity below the security’s effective round-lot size. Under Regulation NMS that round lot can be 100, 40, 10 or 1 share, so every odd lot is under 100 shares, but not every order under 100 shares is an odd lot: 80 shares of a stock with a 40-share round lot is two round lots. A mixed lot contains one or more full round lots plus a smaller remainder.
Regulation NMS assigns each stock’s round lot using its average closing price during the specified evaluation period. The assignments are 100 shares at $250 or less, 40 shares from $250.01 through $1,000, 10 shares from $1,000.01 through $10,000, and 1 share at $10,000.01 or more.
Use the published assignment for the security. That assignment determines the unit used to classify each order.
Formula
Odd-lot condition: 0 < quantity < current round-lot size; mixed-lot remainder = quantity modulo current round-lot size- Current round-lot size is the stock’s published assignment, set from its average closing price during the evaluation period.
- A mixed lot contains at least one round lot plus a nonzero odd-lot remainder.
- A 1-share round lot leaves no positive whole-share quantity below one share.
Odd lot vs round lot: a 40-share example
XYZ has an effective 40-share round lot because its average closing price during the applicable evaluation period placed it in the $250.01 to $1,000 tier.
- 25-share order: 25 < 40, so it is an odd lot
- 80-share order: 80 / 40 = 2 exact round lots
- 95-share order: 95 = 2 × 40 + 15
- Mixed-lot remainder: 95 modulo 40 = 15 shares
The 95-share order is a mixed lot containing an 80-share round-lot component and a 15-share odd-lot remainder. Calling every order under 100 shares an odd lot would misclassify the 80-share order.
The same 95 shares receives a different classification under each assignment. It is odd at 100, mixed at 40 or 10, and exactly 95 full round lots at 1.
How odd-lot quotes and trades appear in market data
Odd-lot executions appear in consolidated transaction data. Best odd-lot quotation information identifies smaller orders with prices inside the round-lot national best bid and offer. The published implementation schedule treats that best-price information separately from aggregated odd-lot depth.
A 20-share quote inside the spread supplies a price and quantity to compare with the planned order. Market depth adds the other displayed price levels; time and sales records completed executions.
Trade count and share volume answer different questions. One hundred one-share executions and one 100-share execution both total 100 shares, with different execution counts. Include quantity and dollars when reading the activity.
Limitations of odd-lot classification
- Classify by the published round-lot assignment. A 25-share order is odd in a stock with a 40-share round lot and 25 full round lots in a stock with a 1-share round lot.
- An odd-lot quote inside the spread offers its price only for its own small size. A larger order fills past the 20-share quote at round-lot prices and deeper levels, so price the whole order against market depth.
- Best odd-lot price information and aggregated odd-lot depth follow separate implementation schedules. Confirm which of the two your feed carries before reading an inside quote from it.
- Read share volume beside trade count: one hundred one-share executions and one 100-share print both add 100 shares.
Bottom line
An odd lot is any quantity below the stock’s assigned round lot, which Regulation NMS sets at 100, 40, 10 or 1 share by price tier. Classify orders with the published assignment rather than a 100-share rule of thumb, and read odd-lot quotes and prints for both price and size.
Clear answers
Frequently Asked Questions
Sources and Further Reading
- SEC: Market Data Infrastructure Fact Sheet
- SEC: NYSE Arca Filing Reflecting the Regulation NMS Round-Lot Definition
- SEC: 2026 Temporary Relief for Certain Odd-Lot Information
How entries are sourced, calculated and updated: editorial methodology.