According to Michael Iachini, managing director of ETF research for Charles Schwab Investment Advisory Inc., the simple formula is -
1. First off, the expense ratio remains as a percentage.
2. The per-year, bid-ask spread percentage is calculated by dividing the current spread with the holding period.
3. Lastly, the commission is taken out whenever you buy or sell a fund, unless the brokerage offers commission free trades. The commission per-year percentage conversion is taken by multiplying the commission fee by 2, divided by the total dollar amount invested and then multiplying by 100.
4. ETF investors can then add up the three numbers to calculate the total annual cost in percent terms.