Fractional shares let an investor buy a slice of a security instead of a full share — useful for low ticket sizes, recurring deposits, and portfolios that need precise allocation without cash drag on high-priced names.
Whilst “own $10 of any stock” sounds clean, in practice custody, corporate actions, voting, and tax lots get messy at the ledger layer. For example, a dividend or split must be allocated across millions of micro-positions without drifting customer balances. We often recommend treating fractional as a product of custody + ledger design, not only a trading-screen feature.
Fractionals are an accounting and custody abstraction over whole-share markets: the broker or custodian holds whole inventory and allocates economic exposure to clients. Failure modes show up in corporate actions, transferability, and reconciliation — where “0.003 shares” must remain correct after every event.