Why ETFs for long-term holding? I don't get it. There are mutual funds with the same index tracking ability that are transaction-fee free?
Where are you buying said funds.
I will use Vanguard + H&L as examples.
Assuming we are talking about a simple index, then we can take the global all cap, vs equivilent ETF.
If buying £100k of it, via ETF on H&L, you will pay £11.95, and likewise another £11.95 to sell it
If you buy the fund version from H&L, there are no trading fee's however you will pay the 0.45% platform fee, This will then be £450 for the year on £100,000
If you are doing this via vanguard, the fee will be £150, as they are 0.15%..
If you decide to buy, once per month, the total cost on H&L, which is the most expensive would be £11.95 per month, or £143.40 per year
That would be like having £32k ish on H&L, and £96K on vanguard. Roughly
Once you'd have more than that, the ETF is actually cheaper following that exact investment strategy.
Now assuming you invest quarterly that number drops a lot, and every year you are saving more vs holding the fund.