Something I don't understand is why any investment (aside from cash equivalents) should be considered acceptable for short term needs:
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If you're selling out of an active MF within 6 months, then you have no business investing in it. Just buy a bunch of index ETFs or a target date fund"
Active bad, passive good?
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These are long term investment products unlike individual securities or ETFs."
It's okay to use any investment so long as it has low/no commissions?
We can dismiss the impact to the fund itself - that's taken care of by the fund's own redemption fee (which goes back into the fund to compensate it for trading costs/market movement). Here we're talking about brokerage fees, not fund redemption fees.
So the question is, from the investor (as opposed to fund) perspective, does it ever make sense to count on index ETFs or target date funds, or individual securities or any (active or index) ETFs, as a place to keep short term (under 6 month) money?
IMHO, the answer is no, with the possible exception of individual securities, if you're buying them because you (think you) see an obvious mispricing that you want to take advantage of and flip quickly.
Actively managed funds (whether open end or ETF)
may be more unpredictable in the short term than indexes, but that doesn't mean one can count on an index fund not taking a dive in the next few months.
Target date funds, especially in the short run, are basically just hybrid funds (glide path significantly affects allocations only over years). With roughly zero correlation between stocks and bonds, sometimes the components will move in opposite directions, sometimes not. You don't know if this time, this month, they're both going to drop.
https://www.ft.com/content/7914a096-48a9-11e8-8ee8-cae73aab7ccb"
in case something comes up and you need to sell"
I read that as an unexpected, large expense (roof blew off, car suddenly died, etc.). If one's six month plus emergency fund isn't enough to handle the rare, unexpected expense, then sure, one will need to sell some longer term investment.
I wouldn't expect a need like that to occur more than once every several years. It's not worth picking a brokerage on the possibility of incurring a $
50 fee every few years. It seems better to focus on routine costs/fees, service, accessibility, etc.