Small fees are a big deal. Also, small fees are mostly a distraction. Both true. Let me explain.
The lowest expense ratio ETFs look identical on a fact sheet: 0.02% here, 0.03% there. The fee is the one return you're guaranteed, and it's negative, so it deserves attention. Take the S&P 500 trio. SPLG at 0.02%, VOO and IVV at 0.03%, SPY at 0.09%. An ETF fee calculator for long term cost will show you that on a big portfolio over decades, the gap between 0.02% and 0.09% becomes tens of thousands of dollars. Same index. Different bill.
But here's the part the fee-chasers skip. Expense ratio is not the total cost of owning a fund. Tracking difference, bid-ask spreads, securities lending revenue: these all move the real number. A 0.03% fund that tracks tightly can beat a 0.02% fund that tracks sloppily. An ETF vs mutual fund expense ratio comparison gets interesting here too, because plenty of index mutual funds now match ETF pricing. Compare the actual fee, not the wrapper. Cheap is good. Cheap and accurate is the actual goal.
My rule of thumb: under 0.10% for core index exposure. Anything above 0.50% is guilty until proven innocent. Active strategies have to earn that fee every single year, and most don't.
And remember the fee is invisible. You never get a bill. It just quietly shaves your returns, which is exactly why it compounds so destructively. The fee you notice least costs you most.
For the fee math across 108 funds, ETFCompare lines up expense ratios and long-term cost side by side. Under the hood, comparisons like this run on an ETF expense ratio comparison database, and some of those databases offer an API for developers. You don't need any of that. Type two tickers into any decent ETF screener and the gap shows up in seconds. Start at etfcompare.fyi.