[ams6110]

Yes. If you dollar-cost-average into funds (e.g. invest the same dollar amount every month), you will automatically buy more shares when the market is low and fewer when the market is high. Long term this is exactly what you want to do, and it doesn't depend on being able to predict price movement.

I even buy gasoline this way, because prices at the pump seem to change almost randomly. I buy $25.00 at a time. So I buy more when the price is low and less when the price is high.

[graedus]

> I even buy gasoline this way, because prices at the pump seem to change almost randomly. I buy $25.00 at a time. So I buy more when the price is low and less when the price is high.

At the risk of a joke flying right over my head, I'll ask how this works. Isn't your gas usage mostly inelastic? Are you going to drive to work less or to the supermarket less because your tank is almost empty due to gas prices being higher? If you're thinking about planning a road trip, do you say "nah, only got half a tank of gas" due to your $25 not buying you as much? Wouldn't it be easier to just look at the price of gas and decide based on that?

[jtolmar]

It works if $25 of gas lasts long enough to get to a different price (harder at a bad price), and your tank has sufficient room to hold $25 of gas (harder at a good price). Those constraints make it worse than real dollar cost averaging, but it should still work.

You can do better if you can predict gas prices but that's sort of the point of DCA - it's a strategy that works without insight.

Edit: this strategy has a higher sample rate when gas prices are bad. This causes a problem if prices are temporally correlated, which they are, unless the sample distance is large enough that the price has enough time to become completely randomized, which is a big ask.

[lucas_membrane]

> a strategy that works without insight

Doesn't work if gas price changes are log-normally distributed.

[paulmd]

My strategy has always been to just plan on refilling around a half tank, and at that point I just fill up the next time I'm near one of the gas stations that I know to have cheap gas. Gives me a little cushion if it's a holiday weekend or something (which always have higher prices) and I avoid driving way out of my way just to save $0.10 per gallon for gas. If it's real insane, you put $10 in the tank to hold you over until prices drop or you can get somewhere cheaper.

Thought that was how most people did it, but I guess my gasoline-investment strategies may not be as savvy as I thought. Gotta pump up those numbers! /s

(it's a bad idea anyway to drive on less than half a tank - during the summer you can overheat your fuel pump, and during the winter you will tend to pick up water in the tank)

Long term you don't really have a choice about not buying gas, it just is what it is. It's funny how people obsess over it, or will go way out of their way for cheaper gas, when most of the time you're talking about a full tank costing you an extra buck or two, and you burn maybe a tank a week. The greedy strategies (fill up when you need it, with a slight preference to cheaper gas when you can get it) are going to produce pretty optimal results so why obsess about it?

[jpetso]

As a city person, I have to disagree about the lack of alternatives. Walking to the grocery store, or if it's really far, cycling to the grocery store, will do wonders for the gas bill.

Yes, that may mean relocating to a part of town where the next grocery store is not 10 miles away.