Two products with the same gross return can end with different balances because the difference in cost builds up over the years.
An example with numbers
As an approximation, compare two net scenarios of 5% and 4% a year. After 20 years, $10,000 would grow to about $26,533 and $21,911. The difference would be about $4,622, with no new contributions or taxes.
Try it with your numbers
Enter both returns in the compound interest calculator. If the return you use already has costs taken out, avoid subtracting them a second time.
Example figures for learning purposes. They are not a recommendation and do not replace professional advice.