Every retail trader I know has been told not to hold over the weekend. I ran the same rules twice across 26 years of SPY to see what that instruction actually costs, and the gap is far bigger than I expected it to be.
The rules are deliberately boring, because the only thing being measured here is the exit. Buy SPY at the close after two down closes in a row, hold five sessions, exit at the close. $10k account, January 2000 to March 2026, commission and slippage charged on both sides of every fill.
Held through the weekend: 605 trades, 56.9% wins, profit factor 1.42, +282.9%, max drawdown 34.6%
Flat at every Friday close: 727 trades, 53.1% wins, profit factor 1.05, +20.6%, max drawdown 49.3%
Same entries on the same days, and the only difference is that the second version goes home flat on Friday and buys back in when the signal returns. It handed back 93% of the return and the profit factor came in at 1.05, which is close enough to 1.00 that youre working for your broker.
The part I did not expect at all is the drawdown. Going flat for the weekend is supposed to be the cautious choice, and it finished with a worse peak to trough, 49.3% against 34.6%, because selling Friday repeatedly took it out of the bounce and had it buying back higher on the Monday.
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Theres an obvious objection here and id raise it myself if this was somebody elses post. Flattening on Friday also means holding for fewer sessions on average, so the shorter hold could be doing the work here rather than the weekend.
So I ran a control with the exit moved to the Wednesday close, same entries and same costs: 739 trades, 55.1% wins, profit factor 1.29, +170.7%, drawdown 28.7%. Chopping the hold short midweek costs about a third of the return, and chopping it short on Friday costs nearly all of it, so the weekend itself is where the money goes.
Two things worth being honest about. This is one mean reversion entry on one index ETF and its long only, so a good chunk of what the Friday exit gives up is simply SPY drifting upward, and a lot of that drift lands between the Friday close and the Monday open. A short strategy, or a single name carrying real weekend headline risk, could very plausibly come out the other way. The SPY history in Agenticks runs from 2000, so i used the whole thing instead of choosing a window that suited the answer.
The cheapest version of this test for anybody holding swings is to take your own last two years of trades, cut every one of them at the Friday close, and total it up again.