What has changed with the round lot size?
On November 3, 2025, the SEC implemented new "Round Lot" definitions under the Market Data Infrastructure (MDI) Rules to enhance market transparency. The new "Round Lot" definitions changed how quote information is displayed based on stock price.
What are the new round lot sizes?
The SEC has established a tiered structure based on stock price:
- $0-$250: 100 shares per round lot
- $250.01-$1,000: 40 shares per round lot
- $1,000.01-$10,000: 10 shares per round lot
- Over $10,000.01: 1 share per round lot
How often will round lot sizes be updated?
Round lot assignments will be updated semi-annually based on each stock's average closing price:
- March evaluation period: Updates effective first business day in May
- September evaluation period: Updates effective first business day in November
Do I need to take any action?
No specific action is required. However, we recommend being aware of these changes when reviewing quotes and placing orders, as they are now in effect.
I am an API user. How does this affect me?
While share-based data has been available through our API for some time, you may wish to verify your configurations properly interpret the new lot size definitions.
When did these changes take effect?
The new round lot definitions were implemented on November 3, 2025.
Who made these changes?
The changes to round lot sizes were mandated by the Securities and Exchange Commission (SEC) as part of their Market Data Infrastructure (MDI) Rules.
Where can I get more information?
For additional details, you can visit the NASDAQ Trader website or contact our Client Services team with specific questions.