Simply stated, an "Odd Lot" is a stock order comprised of fewer shares than a “Round Lot”. The size of a round lot is determined using tiering based on the share price of the stock. The tiering is as follows:
| Share price (average closing price) | Assigned Round Lot Size |
| $0-$250 | 100 shares |
| $250.01-$1000 | 40 shares |
| $1000.01-$10,000 | 10 shares |
| Over $10,000.01 | 1 Share |
- The determination of which tier a stock fall into is based on an “evaluation period” (all trading days in March for May implementation; all trading days in September for the November implementation) of the stock’s average closing price on its primary listing exchange. The assigned round lot size will then become effective on the first business day of May or the first business day of November each year.
- Any number of shares that is a multiple of a round lot is a round lot (e.g., 200 shares of a $100 stock, 80 shares of a $500 stock, etc.).
- An order for a number of shares greater than a round lot, but not a multiple of a round lot, is a “mixed lot.”
- Odd-Lot orders are taken into the order book at the exchange they are routed to. When the exchange is able to match an order from the other side of the book with the odd lot, it will be filled.
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