Algo Trade Fractional Shares With Alpaca and Robinhood

You can now buy and sell fractional shares with both Alpaca and Robinhood. You can trade in notional dollar amounts or with a fractional quantity. This feature is useful for smaller accounts that want to trade more expensive names like AMZN.

2 Min Read Published September 8, 2021 Updated August 6, 2026 Reviewed by Mike Christensen Fact-checked by Mike Christensen

Order Form

In the order form you will now see a new option to choose from called Invest in and you can choose to invest in a shares quantity amount or a notional dollar amount.

If you choose to invest in a dollar amount, when you confirm and submit your order, you will see an estimated quantity based on what the current market price is.

To invest in fractional quantities, just choose Shares from the Invest in dropdown and enter a quantity with a decimal.

Please be aware that each broker supports a different amount of decimal places. TradersPost will validate the number of decimal places if you enter a number of decimal places that is greater than what the broker supports.

Alpaca - supports 9 decimal places¹.
Robinhood - supports fractional share quantities as low as 0.000001 shares².
TradersPost Paper - supports 9 decimal places

Strategy Subscriptions

To enable the use of fractional shares in your automated trading, just go to edit your strategy subscription and scroll down to the Position Size section and check the Use fractional quantity checkbox.

Save your strategy subscription and now you will see that the example entry and exit order are using a fractional quantity instead of a whole number.

Support Brokers

Unfortunately, not all brokers support fractional shares. You can use fractional trading with the following brokers:

Alpaca - You can read more about Alpaca fractional trading here.
Robinhood - You can read more about Robinhood fractional trading here.
TradersPost Paper - You can read more about TradersPost Paper fractional trading here.