Overnight Stock Trading: In the 20% Band, Trades Are Final

Overnight stock trading is about to gain a fence and lose its referee. From Sunday 6 December, US exchanges are scheduled to trade stocks from 9 p.m. to 4 a.m. Eastern time, inside fixed price bands about 20% beyond each stock's close. A trade that lands inside the band at two in the morning will stand, however far it sits from the last sale. Had it printed at seven the evening before, a broker could have asked for it to be broken.

So can you buy stocks overnight? Yes, and sell them, though not yet on an exchange. Robinhood and Interactive Brokers already take orders all night and route them to alternative trading systems, off-exchange venues that each set their own limits. December brings the exchanges into those hours, with one set of bands for everyone and one rule on which trades can be undone.

Soren knows what becomes of a trade once screens forget it. He spent decades on the post-trade side of markets, where trades are matched and settled and a broken one arrives as a notice with a rule number on it. He walks one night of the new session through its rulebook, from the minute the fence goes up to the minute it comes down.

The first thing he marks is a verb. Every document he has open says the session is "expected" or "scheduled" to begin on 6 December. The hedge comes down to plumbing. Feed operators, the processors that carry prices and bands to the public, still have systems to change.

In Soren's notes, the date goes in pencil.

When can you buy and sell stocks overnight?

Until December, the answer depends on your broker. Robinhood's 24 Hour Market runs from Sunday evening to Friday evening and takes only limit orders, in whole shares. Interactive Brokers' session ends at ten to four in the morning. Behind those sessions, each alternative trading system, or ATS, writes its own price limits. Robinhood's help page shows one: a stock trading at $10 at 7:30 p.m. gets bands of $8 and $12.

If the schedule holds, the exchanges join them, and overnight stock trading gets its first market-wide rules. Nasdaq, NYSE Arca and Cboe EDGX are among the exchanges the SEC has already cleared for 23-hour trading. Each evening, from 8 to 9 p.m., the exchanges go quiet while the alternative systems keep trading. At nine the fence goes up, and it stays up until four in the morning, Sunday night through Thursday night.

Saturday sits outside the plan, and trading stocks on weekends would run on one venue's rules instead of the market's. "Five nights, seven hours a night. Thirty-five hours a week, and the weekend gets none of them," Soren says.

How overnight stock trading sets its price band

Where a fence stands depends on where you measure from. Soren hunts for the reference price and finds two. They sit in an amendment to the limit up-limit down plan, the rulebook that already caps price swings during the regular session. It pairs each stock's official close with its last regular-size trade at 7:30 p.m., and the lower edge sits 20% below whichever is lower. The upper edge sits 20% above the higher one. Both edges go out just before nine and hold until four.

That 20% is not the exchanges' idea but the private venues'. According to the SEC's summary, the plan's authors picked it "to align with the 20% static band protections currently employed by ATSs for overnight trading". So the exchanges arrive at night and adopt the house rules.

Twenty percent of an expensive stock is a lot of room. SanDisk closed at $1,482.33 on 13 October. Had its evening trade matched the close, that night's fence would have run from $1,185.86 to $1,778.80 (computed). SanDisk's whole range that day was 5.6% of its close. Its 17.1% slide from the 1 October close would have fit inside a single night. "Twenty percent sounds like a guardrail, but on SanDisk it is three hundred dollars of road," Soren says.

Two reference prices also mean news can only widen the fence. Suppose a stock closes at $100 and a bad headline drags its evening trade down to $80. That puts the fence at $64 to $120. A lone close, the plan's authors worried, "may become stale or unrepresentative" once news breaks after the bell.

Their cure for staleness turned out to be width.

At the cheap end, a floor widens the fence instead. Neither edge may sit closer than $3 to its reference price (a dollar, for stocks under a dollar). A $10 stock's fence runs $7 to $13, 30% each way. Below $15, the floor decides, not the 20%. Leveraged funds multiply both numbers by their leverage, which gives a 3x fund 60% of room either side.

Even the evening snapshot's time is provisional. In August the SEC approved a 7:45 p.m. snapshot. Robinhood's president wrote in on the day of approval to ask for the earlier time, which the alternative systems already use, and a later amendment moved it. That change runs on a temporary order into February.

Can an overnight stock trade be canceled?

Soren has handled enough canceled trades to know how they start. A broker files a complaint, and an exchange measures how far the price strayed. Every US exchange calls it the clearly erroneous rule. Only a member firm can file, so a request has to go through your broker, in writing, within 30 minutes of the trade.

Off-hours, the yardstick is the last sale before the trade. Under Nasdaq's version, a pre-market or after-hours trade can be broken once it sits 20%, 10% or 6% from that sale. Which line applies depends on whether the stock trades up to $25, up to $50 or above.

Inside the regular session, the exchanges already switch the procedure off. A trade made while the limit up-limit down bands were in force and correct "will not be reviewable as clearly erroneous". Only narrow exceptions survive: a missing band, a systems fault, a trade after a halt.

From December the switch reaches the night. Nasdaq's filing, published on 13 October, swaps "Regular Market Hours" in that sentence for "LULD Protected Hours", which adds the overnight stretch. In September the NYSE's exchanges filed the same change, and Cboe's and Nasdaq's other exchanges followed in October. None needed the SEC's approval, so each took effect on filing and starts with the night session. Nasdaq states its purpose plainly: "providing greater certainty to market participants that trades executed with the Overnight Price Bands will stand and not be broken".

Soren checks both rules against SanDisk. At a quarter past seven in the evening, a SanDisk trade about $89 from the last sale crosses the 6% line. A broker can ask for it to be broken. At two in the morning, a trade $290 from the close sits inside the fence and stands. On expensive stocks the switch bites hardest, since above $50 the after-hours line is 6%, against 20% at the cheap end.

Now the quietest hours of the week get the least review.

News makes the gap starker. Take the stock that fell from $100 to $80 after hours. A trade at $118 at two in the morning sits 47.5% above its evening price, and it stands, because the fence runs to $120. Earlier that evening, the same print would have been nearly eight times the 6% line.

You hold the stock, a headline lands at two in the morning, and you send a sell with a limit well under the last price, loose enough to make sure it fills. At that hour the bids are thin, so the order can walk down through them. The last shares go far below the dinner-time price.

Inside the fence, all of those fills stand.

"Every broken trade has two sides. Breaking it rescues whoever made the mistake and takes the price from whoever was quick enough to fill it," Soren says. A rule that trades stand has already picked a side. Finality isn't a favor to the careful, it's a decision about who keeps the price, and inside the fence it stays with whoever filled your mistake.

FINRA, which oversees trading away from the exchanges, is expected to pick the same side. As of 14 October the Federal Register showed no filing from it, so for now this finality belongs to the exchanges alone.

"Your broker's chart draws one unbroken line, and the rules under it change five times a day," Soren says.

None of those borders shows on a chart. So the time stamp on a fill now says as much about whether it can be undone as its price does.

What happens when a stock hits the band?

A fence also has to do something when the price leans on it, and here the night parts ways with the day. By day, 15 seconds pinned at a band forces a pause. Overnight, the plan says there "will not be automatic Trading Pauses during the Overnight Protected Hours if an Overnight Price Band is hit". Venues must block trades and quotes outside the fence. A fence like this is not a brake but a wall, and trading carries on right up against it.

The only brake left is human. The listing exchange may call a regulatory halt, "including when orders are consistently being placed outside the bands or the price bands are otherwise limiting price discovery". Once a halt is called, every exchange rejects orders in the stock, and it "will not reopen during Overnight Protected Hours". In the SEC's words, trading picks up again in "a trading session following the overnight session where there is likely to be more liquidity".

If you hold the stock, how far off is that session? A halt at eleven at night means five hours in a position with no exchange to sell through. Reopening comes no earlier than the four o'clock pre-market, which has no fence at all. That gap is deliberate, so early earnings news can move prices without "the constraints of pricing bands based on the prior day's activity".

"A halt stops the bad prices and your exit with them," Soren says.

A halt binds only the venues inside the plan, though. Tokens and contracts on the same shares elsewhere can keep quoting. That is how a stock market circuit breaker can stop an exchange without stopping the price.

What to set before 9 p.m.

That shifts protection onto the order you leave overnight. Drawing the fence is the exchange's job, and the limit price is yours. After nine on an exchange, your limit is the only line on the trade that you set.

Soren works the fence out before he places anything. "The band isn't a stop-loss, it's a limit on how wrong a print can be," he says. He multiplies the lower of the close and the evening price by 0.8 and the higher by 1.2. If 20% of a price comes to less than $3, he pushes that edge out to $3, and a leveraged fund gets both numbers multiplied by its leverage.

Some venues make part of that choice for you, as Robinhood does by refusing anything but limit orders at night. An alternative system may also reject a limit priced outside its band. If a venue does accept an order with no limit at night, it can fill anywhere inside the fence. On an exchange, that fill stands. On anything under $15, and on every leveraged fund, the fence runs wider than it sounds, so a loose limit costs the most there.

Set tight, a resting limit does what the fence won't: it fills at your price or better, or not at all. Practicing that in a paper account has one known flaw. A paper limit fill can price at a touch that a live queue would have skipped.

A fence written to be replaced

None of Soren's numbers is permanent, and the plan says so. Its bands are a first phase. Its authors will report on the first full quarter of night trading, January to March if December holds, and then propose a second phase to replace the interim bands. Meanwhile the evening snapshot runs on a temporary order, and comments on Nasdaq's filing run to early November. Soren pencils the end of March beside the first date.

The exchanges will learn where the fence belongs from the trades that land inside it, and none of those trades can be taken back.

Tonight, mark a fence for Nvidia, Tesla or another stock the simulator trades around the clock, at 0.8 and 1.2 times its US close. Leave a limit buy at the price you'd accept at three in the morning, and check the night's low against all three numbers when you wake. Nothing in the simulator draws that fence for you, so the only line that decided anything overnight was the limit you typed.

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