When Your Broker Acts Without You
Five published rules let someone else act in your account without asking: a maintenance call, an assignment, the pattern day trader rule, a trading halt and a corporate action. You cannot prevent any of the five. You can compute all of them before you hold a position, and the arithmetic takes an evening.
Prerequisites: Lesson 14, which named the maintenance level this lesson turns into a price, and lesson 13, because only one of the four objects can be assigned to you overnight.
None of these rules exists to catch you out. Your broker lends you money and would like it back, and an exchange with no brakes produces prices nobody can trade against. What ends accounts is not the rules; it is meeting one of them for the first time at the worst possible moment, in a position sized as though it did not exist.
The price at which your broker starts selling
Lesson 14 gave you the maintenance level as a percentage. Turning it into a price takes one observation: when the position falls, your loan does not fall with it. The loan is a fixed number of dollars. Only your equity absorbs the loss, which is why the threshold arrives sooner than the percentage suggests.
loan = position value × (1 − your share of it)
call value = loan ÷ (1 − maintenance requirement)
fall to the call = 1 − call value ÷ position value
Note what is absent from all three lines. Your entry price is not there, your reasoning is not there, and your stop is not there. Two traders holding the same loan against the same position have the same call price, whether one is up on it and the other down.
Lesson 14 named the two requirements. Here are the numbers and where they are written down, because you will need both to use the formula. Regulation T is what caps the initial borrow at half the position. The maintenance level has a regulatory floor of 25 per cent under FINRA Rule 4210, and your broker may demand more — commonly 30 per cent, higher still on volatile names. Only the second of the two sets the call price, and only your own margin agreement tells you which figure your broker actually applies to what you hold.
One error is worth heading off, because it is the one almost everybody makes: reading the requirement as though it were the fall. They are different numbers. A 30 per cent maintenance requirement does not mean the position may fall 30 per cent. On a position where half is borrowed it means the position may fall 28.6 per cent, as the worked example below shows, and on a more leveraged position it means far less than that. The requirement is a level your equity must stay above, not a distance the price is allowed to travel.
A stop does not help you here, and the reason is worth stating exactly. A stop is an instruction to the market, to trade at a price. A maintenance call is an instruction to the account holder, and if you do not meet it the liquidation belongs to the broker — their timing, their choice of which position to sell, usually whichever is easiest rather than whichever you would pick. In a gap the two arrive together and the stop is the slower of them, because it can only work against trades that print and the broker does not have to wait for those.
Assignment: shares you did not order
If you are short an option, the person on the other side may exercise it, and an American-style option can be exercised on any business day rather than only at expiry. You learn about it overnight; the position is simply there in the morning.
Most early exercise is not a whim, and one case dominates. A call holder receives no dividend. Exercise the day before the stock goes ex-dividend and they own the shares in time to collect it, and they will do that whenever the dividend is worth more than the time value they throw away by exercising early. So one comparison predicts it: the dividend per share against the remaining extrinsic value of the call. Take a $50 stock about to go ex-dividend by $0.60, and a $48 call trading at $2.15. With the stock at $50 the contract holds $2.00 of intrinsic value, so $0.15 of it is time value. The holder throws away 15 cents to collect 60 cents, and they will. If the dividend is larger than the extrinsic value, expect to be assigned. That is not a rule of thumb but the arithmetic of the person on the other side, and they have every reason to run it.
For a covered call the consequence is concrete. On those numbers your shares go at $48 while the stock is $50, the $0.60 you were holding them for is collected by somebody else, and what you keep is the premium you were paid weeks ago.
Expiry has its own version, and it carries a name worth knowing because you will meet it elsewhere: a short option sitting within a few cents of its strike into Friday’s close is pin risk, and it may or may not be exercised. You will not know which until the market has shut, and Monday can open with a position you did not choose and could not have hedged over the weekend. Closing it on Friday costs a spread, and that is the cheapest insurance in this lesson.
The pattern day trader rule
In a United States margin account, four or more day trades — opening and closing the same security within one session — across five rolling business days makes you a pattern day trader, and from that point the account must hold $25,000. Three details are not obvious from the name. The window is rolling, so there is no Monday reset. It counts round trips rather than orders, so scaling out of one position in three pieces is one day trade and not three. And it applies to margin accounts; a cash account escapes it entirely and meets settlement instead, which constrains you differently but no less: proceeds cannot be re-used until they settle, so the same capital cannot be turned over freely either way.
The useful response is not to route around the rule. A cap of three day trades a week is telling you something about position size: a trader who wants four has chosen a style their account cannot fund.
Halts, and why a stop is not a guarantee
United States markets run price bands around a rolling average. Trade outside the band for fifteen seconds and the security halts for five minutes; the band is a percentage, it is wider for cheaper stocks, it narrows for the most liquid ones, and it doubles in the last twenty-five minutes of the session, which is when a stop is most likely to be reached and least likely to behave. What matters for you is what a halt does to a resting order, and the answer is nothing at all — which is worse than it sounds. A stop is triggered by trades, and during a halt there are none. When trading resumes it resumes through an auction rather than a continuation, so your stop joins that auction as a market order, at the widest spread of the day.
Corporate actions
The last of the five is the one nobody plans for, because it looks like the company’s business rather than yours. A split multiplies your share count and divides the price. A reverse split does the opposite. A special dividend or a spin-off moves the printed price by the value that left the company. In each case the price on your chart changes without anything having happened to what the company is worth, and your resting orders are usually adjusted — usually, not always, and not always well.
Which matters most if you trade on levels. A corporate action can trip every price-based order you hold at once, for a reason that has nothing to do with supply and demand, and a stop placed under a support level is simply somewhere else the following morning. The defensive move is small: check the corporate actions calendar for anything you hold overnight, and re-place level-based orders after one rather than assuming the adjustment did what you wanted.
The whole of it in one grid
Take it slowly once. You buy $20,000 of stock with $10,000 of your own money, so the loan is $10,000. Your broker requires equity to stay above 30 per cent of whatever the position is currently worth. The position can therefore fall to $10,000 ÷ 0.70 = $14,286 before that fails, and at that value your equity is exactly 30 per cent. From $20,000 that is a fall of 28.6 per cent. Below it the broker asks for money, and if it does not arrive quickly they sell — on their timetable, in whichever position is easiest to sell, not the one you would have chosen.
Now the same arithmetic across every level of borrowing, which is the artefact worth keeping:
| Your share of the position | Leverage | Fall to a call at 25% | at 30% | at 35% |
|---|---|---|---|---|
| 100%, no loan | 1.00× | never | never | never |
| 75% | 1.33× | 66.7% | 64.3% | 61.5% |
| 60% | 1.67× | 46.7% | 42.9% | 38.5% |
| 50%, the most you may borrow to open | 2.00× | 33.3% | 28.6% | 23.1% |
| 40% | 2.50× | 20.0% | 14.3% | 7.7% |
| 35% | 2.86× | 13.3% | 7.1% | 0.0% |
| 33.3% | 3.00× | 11.1% | 4.8% | below it already |
Read the fourth row first, because it is the only one you can open at: the initial rule caps borrowing at half, so 2.00× is where a securities account starts. Every row beneath it is a state you arrive at, once the market has eaten into the half that was yours. Nobody chooses the 35 per cent row; they choose the 50 per cent row and then have a bad fortnight.
Which is what makes the bottom rows worth reading closely. At 2.86× against a 30 per cent requirement, a fall of 7.1 per cent brings the call, and 7.1 per cent is under three average days for the mid-cap row of lesson 12’s table. The last cell is not a rounding artefact either: at three times leverage against a 35 per cent requirement you are beneath the threshold the moment you arrive there, which is why a broker holding you to 35 per cent will sell rather than ask.
What this does not settle
That any of these can be avoided by trading well. They are terms in an agreement you signed and rules an exchange publishes, and skill does not enter into them. What the lesson claims is narrower and more useful: all five are computable in advance, and whether one is an inconvenience or a catastrophe usually turns on whether the number was on paper before the position was.
Nor are the figures universal. The 25 per cent floor, the $25,000 threshold and the five-day window are United States rules, and your broker’s house requirement will sit above the regulatory floor, higher still on volatile names. The shape of the arithmetic travels; the constants do not, and the ones that bind you are in your own margin agreement.
And the call price is not a prediction of ruin. It is the level at which someone else acquires the right to act, which is a different and much earlier thing than losing everything. How likely you are to reach it is a question about variance, and that is lesson 22.
The call price above also assumes the position is the account. A real margin account is netted: the requirement is computed across everything you hold, so the number you write down for one holding is its call price only while it is your only holding. Two positions that fall together can bring a call that neither would have brought alone, and the arithmetic for that is not on this page.
And five is the number of rules that are published, not the number of ways somebody can act without you. A broker may raise a house requirement on a specific name overnight, recall a borrow and close a short for you, or restrict opening trades in a security entirely, and all three happened to ordinary retail accounts in 2021. None is an exchange rule and none is in the five. They are in your margin agreement, in language that reserves the right rather than describing the circumstance, which is exactly why they are not computable in advance the way the five above are.
Every item here has one shape: an outside party acts on your position under a published rule, at a moment you did not pick. You cannot stop any of it. You can know all of it before you open the position.
Problems
- Write the sentence. Open your account and write down the position value and the margin loan, then find the maintenance requirement in your margin agreement — the house requirement for volatile names is often listed separately from the general one. Compute loan ÷ (1 − requirement), express it as a fall from where you are now, and then write one line: “if my account falls to ____, my broker sells before I do.” Put it where you will see it while deciding how much to buy.
- Has that fall happened? Take the percentage you just computed and go looking for it in the last two years of the thing you actually hold. If a fall that size has happened twice, it is not a tail risk you are describing but an ordinary quarter, and the position is the wrong size rather than the rule unfair.
- Count the round trips. Count your round trips over the last five business days and put the number beside your account balance. If it is three or more and the balance is anywhere near $25,000, you are one trade away from a restriction you have not planned for — and the useful question is not how to avoid the rule but what a style needing four trades a week implies about the size of each one.
Sources. FINRA Rule 4210, which carries both halves of the first and third sections: the 25 per cent maintenance floor and the pattern day trader provisions, including the definition of a day trade that the rule actually counts. Options Clearing Corporation, Characteristics and Risks of Standardized Options — the same disclosure lesson 13 cited for the asymmetry between buying and writing, read this time for what it says about exercise and assignment — and, in its section on adjustments, for how a contract is changed when the underlying has a corporate action. And the National Market System Plan to Address Extraordinary Market Volatility, the limit up-limit down plan, which is where the bands and the five-minute halt are actually specified rather than described.
You now know the five points at which the decision stops being yours. The next lesson asks a harder question about a much safer-looking place: what a simulator can teach you, and what it structurally cannot.
What You Are Actually Buying
Only one of the four objects can be assigned to you overnight.
Read Lesson →Margin and Leverage
The maintenance level, which this lesson converts into a price.
Read Lesson →Position Sizing
The decision that determines whether any of these rules ever reaches you.
Read Lesson →Where the Stop Goes
Why a stop is a tool and not a guarantee; the halt is the sharpest case.
Read Lesson →Educational only. Trading involves substantial risk of loss. Not financial advice. Past performance does not guarantee future results.
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