Analyzing the question "Does it matter what day of the week you DCA?"

You might wonder what day of the week is historically the best day of the week to buy, or if there is even a best day of the week. I thought it would be interesting to see if there was a clear answer to this question, so I analyzed price data for ETH and BTC to see what it revealed.

To start with, I took ETH price data for the previous year and then calculated how much ETH you could buy over that period if you always invested the same amount in dollars (I used $100 per week) on each respective day of the week, starting with Monday August 3, 2020 and continuing through Sunday August 1, 2021.

So in each case, $5200 was invested, but how much Ether did we end up with? It turns out we got slightly more ETH if we always bought on a Tuesday, and the least if we always bought on a Sunday. Here are the complete results:

ETH DCA Investment, Aug 2020 through Aug 2021

All of the results are pretty close as you probably expected. And even "poor Mr. Sunday" made a whopping 278% on his money, so he isn't exactly upset, but Mr. Tuesday made $228 more over the same period, so I guess the first round is on him. Interesting, but this is just one period of time with one coin.

Next I got a larger set of data for BTC, from 2017 through 2021, and ran the same experiment. Now there were 242 weeks of investing the same $100, so did Mr. Tuesday still come out ahead, and was Mr. Sunday still the laggard?

This time it turned out that Mr. Monday was the winner, and Mr. Sunday was the loser again. But again, everybody did really well. Here are the results:

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BTC DCA Investment, Jan 2 2017 through Aug 8, 2021

Since the BTC data set is larger, I also thought it would be interesting to see out of the 242 weeks, how often was each day of the week the "best day" for that week? Here is a histogram that shows the results:

Best day of the week for BTC, Jan 2 2017 through Aug 8, 2021

Consistent with the composite results, Monday was more likely to be the best day of the week, beating the other days of the week 68 times out of 242. But interestingly, Sundays and Fridays were not the least-likely to be the best day of the week, Thursday was. This probably indicates just that the overall performance of Friday and Sunday buying were brought down by just a few particular weeks.

So over all, it doesn't seem like it makes much difference what day of the week you buy nearly as much as the fact that you consistently bought and held. However, maybe the first couple days of the week really are the best; I could speculate on why market psychology might be worse at the start of the work week but that would just be guessing.

What do you think?

EDIT: I had a mistake in the data range for the table of results for BTC - it has been updated.

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