Systems and methods to rebalance portfolios of securities

A system for rebalancing a client's portfolio of securities, comprising:

• a client device with a client interface that in operation is configured to receive a client's rebalance order that includes fraction shares;
• a host server coupled to the client device which in operation executes logic resources for carrying out transactions for a client;
• a pricing engine coupled to the client device;
• a transformable inventory account coupled to the client device;
• a targets engine coupled to the client device and which determines a target number of long and shorted shares of a security to be held by the inventory account;
• a trading engine coupled to the client device, the trading engine in operation is configured to process a client's rebalance order of a client's portfolio in real time, wherein the client receives a list of current positions, selects a share-weighted portfolio, chooses an alternate weighting, and decides to:
• (i) add funds, (ii) remove funds or (iii) rebalance the share-weighted portfolio, the trading engine in operation processing a client buy, sell, sell short, or buy to cover order, wherein for a buy order the trading engine fills the buy order for both whole and fraction shares from the inventory account if there is sufficient inventory in the inventory account, when there is insufficient inventory for the buy order the trading engine completes a purchase of fraction shares first from the inventory account and then purchases the remainder of the buy order from the market, when the inventory account can not fill any of the buy order the trading engine purchases the entire buy order from the market and in the same order purchases a target of shares set by the targets engine for the inventory account.