Overnight and Weekend Gap Risk, Measured
Overnight risk is the chance that a position opens the next session far from where it closed, because news arrived while the regular market was shut. A stop order cannot prevent it: if the stock opens past the stop, the order fills at the open, so the loss can be several times the planned one.
Overnight risk is the risk of holding a position while the market you trade in is closed. It shows up on the chart as an opening gap: the first trade of the day prints somewhere other than the last trade of the day before.
How it works
News does not wait for the regular session. Earnings reports, guidance changes, court rulings, index decisions and events abroad often land after the close or before the open. By the time the regular session starts, buyers and sellers have already repriced, and the stock opens where they agree, not where it closed.
Why a stop does not cap a gap
A stop order cannot trade at a price nobody offered. A sell stop at $48 becomes a market order once the stock trades at or below $48. If the first trade of the day is $44, that is where the order is triggered, and it fills at or near $44. The stop loss did its job of getting out; it could not choose the price.
A weekend is the same risk, stretched. Friday’s close to Monday’s open covers two and a half days of news. A holiday weekend adds another day.
Extended hours do not remove it. Pre-market and after-hours trading exist, but volume is thin and spreads are wide, so a position can often not be closed at a sensible price when the news breaks. Nasdaq plans an overnight session from 6 December 2026 (SEC-approved April 2026; launch depends on operational readiness), which would narrow the closed window for Nasdaq-listed trading rather than end it.
A worked example
A hypothetical position. A $10,000 account buys 200 shares of a $50.00 stock with a stop at $48.00. The planned risk is $2.00 a share, or $400, which is 4% of the account.
The company reports after the close and the stock opens at $44.00. The stop triggers at the open and fills at about $44.00. The loss is $6.00 a share, or $1,200. That is 12% of the account, three times the planned $400, and nothing about the stop was wrong.
The fix is in the sizing, not the stop. If a gap of $6.00 is plausible for this stock over a report, sizing on that distance instead of the $2.00 stop gives $400 / $6.00, or about 66 shares. The position sizing page covers the method. The cost of the fix is a smaller position on every trade held through the event, whether or not the gap arrives.
The original data
Every swing rule in these backtests held overnight. The tests ran in TradingView’s Strategy Tester in August 2026 on seven stocks, AAPL, MSFT, GOOGL, AMZN, NVDA, META and TSLA, from January 2015 to August 2026. Signals are known at the close and fill at the next open, so even the fastest trade spans a night. For the eight rules in the chart above, the per-stock average hold ran from 3 bars to 15 bars, and most of the rules had no stop at all.
Buying the gap down, tested
One rule is built directly on the overnight gap. It buys when a stock opens at least 1% below the prior close while the close is above its 200-day average, fills at the next open, and sells after the first higher close. The average trade lasted 3 bars.
On the seven winners, 473 of 757 trades closed higher, which is 62.48%. The test called a result good only with at least 60% of trades closing higher, a profit factor of 1.3 or better, and 30 or more trades. It cleared all three on six of seven, failing only on NVDA, where 57.45% of 141 trades closed higher and the worst drawdown reached 42.86%.
Then the same code ran on five stocks that lagged the S&P 500: INTC, PYPL, DIS, NKE and WBA, over the same window. Pooled, 155 of 289 trades closed higher, which is 53.63%, close to a coin flip. It cleared the bars on none. On Disney only 22 of 49 trades closed higher, the profit factor was 0.650, and the rule lost 14.63%. For Walgreens the window closes early, on 27 Aug 2025, when its shares stopped trading.
Said plainly: whether a gap down gets bought back depends on the stock, and these seven stocks went up for a decade. On winners, a 1% gap down was more often recovered than not. On the five that lagged the market, it was close to even, and on Disney it was worse than even. The second list was picked because it trailed the market, so it leans the other way; an ordinary stock would likely sit between.
What the files do not measure. They do not split each trade’s result into the overnight part and the daytime part, and they do not count how many gaps occurred. They measure rules that held through gaps. The rows are published in the per-ticker results table and the five-stock retest. All of it is simulated past performance on a small, chosen set of tickers, not a forecast.
When it fails
Planning around it fails when the stop is treated as the maximum loss. It is the maximum loss only while the stock trades continuously through the stop price. Over a close, it is a trigger, not a cap.
It fails around scheduled events. Earnings dates are known in advance, and a report is one of the commonest reasons for a large gap. Holding through one on a full-size position means accepting a gap risk the stop cannot limit.
It fails for rules with long holds. The five-day low rule averaged 10 to 14 bars across the seven stocks, so each trade carried ten or more overnight gaps and usually a weekend. On TSLA its worst drawdown was 53.98%. With no stop, every gap in that stretch went straight into the account.
It fails when gap-down buying is treated as a sure recovery. The gap fill idea is popular, but the gap-down rule here closed higher on 22 of 49 Disney trades and lost money. On the stocks that were not rising, buying the gap was close to a coin flip before costs.
And it fails on leverage. A gap that costs an unleveraged account 12% costs a two-times margined one about 24%, and can trigger a margin call before the trader can act.
Related
The opening gap page explains what a gap is and why it appears on the chart. The stop loss page covers what a stop order can and cannot do, which is the heart of this risk. And position sizing is where overnight risk is actually managed, by sizing on the gap you could take rather than the stop you hope to get.
Size a swing position on the loss it would take if the stock opened well past the stop, not on the stop distance alone. For a position held over an earnings report, the gap is the risk that matters.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.