VOO is obviously superior when considering just the expense ratio. For most individual investors, VOO is a preferable option due to its lower expense ratio (0.03%) compared to SPY's 0.0945% expense ratio. However, this is not always the case.
The trading spread benefit of SPY may eventually offset the expenditure ratio disadvantage if you trade frequently. It would take 13 trades annually to offset SPY's 0.0645% annual expenditure ratio disadvantage if you were able to save 0.005% on each trade by switching from VOO to SPY. Now you know voo vs spy
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