# Odd lot Odd lot is a stock trade or order for fewer shares than the applicable round-lot size, commonly fewer than 100 shares for a US-listed stock. ## What it means Share counts affect how a stock order is classified. An odd lot contains fewer shares than the applicable round-lot size. A round lot is commonly 100 shares for a US-listed stock, but the applicable size can vary with the stock's price and the market's rules. Check the applicable size rather than assuming it is always 100 shares. An odd lot describes a *number of whole shares*, not a fraction of a share. A 25-share order can be an odd lot; a 0.5-share order involves fractional shares. An order containing one or more full round lots plus a remainder is generally called a mixed lot: if the round-lot size is 100 shares, 125 shares consists of a 100-share round lot and a 25-share odd-lot remainder. ## How it is calculated To classify an order, compare its whole-share quantity with the applicable round-lot size: `odd lot if 0 < Q < R`, where `Q` is the number of whole shares in the order and `R` is the applicable round-lot size, in shares. This identifies an order made entirely of an odd lot. For an order of at least one round lot, the remainder is `M = Q mod R`, where `M` is the remaining number of shares after dividing `Q` by `R`. If `M > 0`, the order is a mixed lot; its remainder is smaller than `R`. The classification uses share counts, not the order's dollar value. Market rules and data displays may distinguish among odd-lot orders, quotes and completed trades, so the context matters. ## Worked example Assume a hypothetical stock has an applicable round-lot size of 100 shares and a hypothetical price of US$20 per share. 1. A 25-share order is an odd lot because `0 < 25 < 100`. Its indicated value at US$20 per share is `25 × US$20 = US$500`, before execution costs. 2. A 100-share order is one round lot. At the same price, its indicated value is US$2,000. 3. A 125-share order contains one round lot and an odd-lot remainder: `125 mod 100 = 25` shares. It is a mixed lot, not an order made entirely of an odd lot. The US$20 price helps illustrate order value; changing the price alone does not change the share-count calculation while the applicable round-lot size remains 100 shares. ## Why it matters before you trade Odd lots may be displayed or handled differently from round-lot quotes under applicable market rules. In particular, an odd-lot quote may show a price inside a displayed round-lot bid and ask without being reflected in a quote display limited to round lots. That does not mean every odd-lot order receives a better or worse execution: available liquidity, order type, routing and market conditions still matter. For a small order, the bid-ask spread can be significant relative to its dollar value. A quoted price is not necessarily the price at which the entire order will fill. A limit price sets a price boundary for execution, but it does not guarantee a fill. If an order fills in pieces, compare its actual fill prices and quantities with the quote or reference price used in the pre-trade check. ## How PreTrAIde uses it The product facts do not state that PreTrAIde separately identifies odd lots or applies odd-lot-specific quote rules. Its Pre-trade analysis takes each stock's side, quantity and execution conditions as part of a basket and estimates factors including bid-ask spread, participation in daily volume, market impact and execution scores. It returns a GO, NO-GO or MODIFY verdict with reasoning and a suggested execution strategy. These are decision-support estimates, not a promise of an odd-lot fill or a particular execution price. Users place orders with their own broker; PreTrAIde does not transmit or execute them. ## Common mistakes - **Assuming every round lot is 100 shares.** Confirm the applicable size for the stock and market. - **Calling 125 shares an odd lot when the round-lot size is 100.** It is a mixed lot with a 25-share odd-lot remainder. - **Confusing odd lots with fractional shares.** An odd lot can contain only whole shares. - **Treating quote visibility as a fill guarantee.** Whether an odd-lot quote appears in a particular display does not establish the price or quantity available to an individual order. - **Ignoring costs because the order is small.** Spread and other execution costs can still affect the result. --- Source: https://pretraide.com/glossary/odd-lot