Reg T Sets 50 Percent. The Maintenance Call Lands at a 33 Percent Drop.

Two percentages govern a margined stock position, and they are written by different bodies. The Federal Reserve Board fixes the deposit needed to open the position. FINRA fixes the equity that has to remain in the account afterward. Both figures are quoted constantly. The distance between them is quoted far less often, and that distance is what decides the price at which a maintenance call arrives.

Between a 50 percent initial requirement and the 25 percent maintenance floor written in the rule, the tolerated decline is 33.33 percent. It is not 25 percent, and it is not the 50 percent that the deposit might suggest. On the short side, where the initial requirement is the same 50 percent but the maintenance requirement is 30 percent, the tolerated adverse move is 15.38 percent. The two sides of one account sit about 2.17 times apart, and the difference is arithmetic rather than judgment.

What follows quotes the operative text of both rules, works the trigger prices for a 200-share position, shows how a house requirement moves the line, and then reads the monthly FINRA series that describes margin borrowing in aggregate. Every price, ratio and dollar figure below, other than the reported FINRA series itself, is this article’s calculation from the quoted rule text.

Two rulebooks, two percentages

The initial requirement comes from Regulation T. Paragraph (a) of eCFR, 12 CFR 220.12 Supplement: margin requirements sets the figure for a margin equity security at “50 percent of the current market value of the security or the percentage set by the regulatory authority where the trade occurs, whichever is greater.” The clause after the “or” carries more weight than the number in front of it. Fifty percent is a floor written by the Board. The regulatory authority where the trade occurs may require more, and the greater of the two governs.

The maintenance requirement comes from FINRA. The lead-in to paragraph (c) of FINRA Rule 4210, Margin Requirements reads: “The margin which must be maintained in all accounts of customers, except as set forth in paragraph (e), (f) or (g) and for cash accounts subject to other provisions of this Rule, shall be as follows:” The first item under that lead-in, paragraph (c)(1), is “25 percent of the current market value of all margin securities, as defined in Section 220.2 of Regulation T, except for security futures contracts, ‘long’ in the account”. Paragraph (c) runs through (c)(6), and each subparagraph names the class of position it covers.

The two rules measure different objects. Regulation T measures a deposit against a purchase at the moment of purchase. Rule 4210 measures equity against current market value on every day the position stays open. Because the debit balance is fixed while market value moves, the two percentages describe the same account only on the first day.

Where the maintenance line sits

Take 200 shares bought at $50.00. Market value is $10,000. A 50 percent Regulation T deposit is $5,000, which leaves a debit balance of $5,000. That debit does not move with the price; interest aside, it is a fixed number. Equity is market value minus the debit, and the maintenance requirement is a percentage of market value. As the price falls, one of those falls at full speed and the other falls at a quarter speed.

Price	Market value	Equity	Equity share
$50.00	$10,000	$5,000	50.0 percent
$44.00	$8,800	$3,800	43.2 percent
$38.00	$7,600	$2,600	34.2 percent
$33.33	$6,666.67	$1,666.67	25.0 percent
$30.00	$6,000	$1,000	16.7 percent

The line is reached where equity equals the requirement. With P as the share price, equity is 200P − 5,000 and the requirement is 0.25 × 200P, or 50P. Setting them equal gives 150P = 5,000 and P = $33.33. In general form, the tolerated decline is one minus the debit fraction divided by one minus the maintenance rate: 1 − 0.50 ÷ 0.75, which is 33.33 percent.

At that price the market value is $6,666.67 and the equity is $1,666.67, exactly 25 percent. The position has lost $3,333.33, which is two thirds of the original deposit. A trader who budgeted the deposit as the loss tolerance has already used two thirds of it at the point where the account stops being self-directed, because a maintenance call converts the next decision from a choice into a deadline.

A house requirement moves the line

Rule 4210 does not present 25 percent as the operative number for any particular account. Paragraph (d)(1) directs members to establish procedures to, among other things, “review the need for instituting higher margin requirements, mark-to-markets and collateral deposits than are required by this Rule for individual securities or customer accounts.” The rule sets a floor and then instructs the member to consider raising it, security by security and account by account.

The rule also contains a step that is not a percentage adjustment at all. Paragraph (c)(6) requires “100 percent of the current market value for each non-margin eligible equity security held ‘long’ in the account.” A security that loses margin eligibility does not move to a stricter percentage on a sliding scale; it moves to full cash coverage, and the equity that was financing it has to come from somewhere else in the account.

Between those two poles, the effect of a house rate on the tolerated decline is steeper than it looks. Each five-point increase in the maintenance rate removes more room than the previous one, because the denominator in the ratio is shrinking.

Maintenance rate	Decline tolerated from a 50 percent entry
25 percent (the Rule 4210 floor)	33.3 percent
30 percent	28.6 percent
35 percent	23.1 percent
40 percent	16.7 percent
50 percent	0.0 percent

The last row is the one worth sitting with. If a broker applies a 50 percent house maintenance requirement to a concentrated or newly volatile name, a position opened at the Regulation T minimum is at its maintenance line on the day it is opened. No decline is required. The call can be generated by a change in the broker’s classification of the security rather than by any move in the market.

The short side is not a mirror

Regulation T treats a short sale of a nonexempted security under paragraph (c), where the requirement is “150 percent of the current market value of the security; or” the alternative in paragraph (c)(2) for positions covered by an exchangeable or convertible security. The 150 percent figure is the whole credit in the account rather than a new deposit: the sale proceeds supply 100 percent and the deposit supplies the remaining 50 percent.

Maintenance on the short side sits in Rule 4210(c)(3), which requires “$5.00 per share or 30 percent of the current market value, whichever amount is greater, of each stock ‘short’ in the account selling at $5.00 per share or above; plus”. Two things follow from that sentence. The percentage is 30 rather than 25, and the subparagraph states its own price range: it addresses stock short in the account selling at $5.00 per share or above. Inside that range the $5.00 per share term is the greater of the two whenever 30 percent of the price falls below $5.00, which is at prices from $5.00 up to $16.67.

Run the same 200 shares at $50.00 short. Proceeds of $10,000 plus a $5,000 deposit give a credit balance of $15,000. Equity is 15,000 − 200P and the requirement is 0.30 × 200P, or 60P. Setting them equal gives 260P = 15,000 and P = $57.69, a rise of 15.38 percent. The general form is 1.50 ÷ 1.30 − 1.

The asymmetry has a second layer. At the long trigger the account has lost $3,333.33 of a $5,000 deposit. At the short trigger it has lost $1,538.46, about 30.8 percent of the same deposit. The short position reaches its call after a smaller price move and after a much smaller share of the deposit has been consumed, because the requirement grows as the position moves against it while the long position’s requirement shrinks. Sizing a short as though it were a long with the sign reversed misstates the distance to the call by roughly a factor of two.

What the aggregate series does and does not say

FINRA publishes a monthly series on the size of this borrowing. FINRA, Margin Statistics publishes it with this description: “Pursuant to FINRA Rule 4521(d), FINRA member firms carrying margin accounts for customers are required to submit, on a settlement date basis, as of the last business day of the month, the following customer information: the total of all debit balances in securities margin accounts; and the total of all free credit balances in all cash accounts and all securities margin accounts.”

Over the twelve months to July 2026 the debit balance total went from $1,022,548 million to $1,417,225 million, a rise of 38.6 percent. The path was not smooth. It slipped from January to March 2026, then ran from $1,220,922 million in March to $1,502,072 million in June, up 23.0 percent in three months, and then fell 5.6 percent in July. Free credit balances in July 2026 were $205,132 million in cash accounts and $217,305 million in margin accounts, so reported debits were about 3.4 times reported free credits. Restated in billions, which is how the chart below plots it, the series runs from 1,022.5 in July 2025 to a June peak of 1,502.1 and back to 1,417.2.

The series is useful, and it is narrower than the uses it is usually put to. Three limits sit in the rule that creates it. FINRA Rule 4521, paragraph (d) provides that “Reports are due as promptly as possible after the last business day of the month, but in no event later than the sixth business day of the following month.” That is a submission deadline for members, and FINRA’s own publication of the table follows it separately. Counting only days the equity markets are open, the sixth business day of September 2026 falls on September 9, because Labor Day on September 7 is a market holiday. As of the first week of September 2026, the most recent row on the page was July 2026.

The second limit is that the figure is a month-end snapshot on a settlement date basis. Intra-month peaks and the forced selling that can follow them do not appear at all. A month that contained a violent mid-month drawdown and a full recovery can print a month-end total that looks placid.

The third limit is that a total is not a distribution. A 23.0 percent rise in aggregate debits over three months is consistent with more accounts borrowing, with the same accounts borrowing more, or with the same borrowing against shares that simply rose in price. None of those tell a reader how many accounts sit near a maintenance line, because the series reports no equity percentages at all. The distance to a call is an account-level number, and this series does not carry it.

What Would Invalidate This

• A house requirement above the rule floor. Every decline figure here assumes maintenance at the Rule 4210(c)(1) floor of 25 percent long and the (c)(3) rate of 30 percent short. A broker applying 35 or 40 percent produces the shorter runways in the second table, and paragraph (d)(1) points members toward exactly that review.
• A higher initial requirement. Paragraph (a) of 12 CFR 220.12 defers to the regulatory authority where the trade occurs when that authority sets a higher percentage. If the entry was financed at 60 percent rather than 50, the tolerated decline widens accordingly.
• Loss of margin eligibility. Rule 4210(c)(6) moves a non-margin eligible equity security to 100 percent of current market value. When that reclassification happens, the arithmetic above stops describing the position.
• Concentration and pattern-based add-ons. Brokers apply additional requirements to concentrated positions and to certain account patterns. Those sit outside the two percentages quoted here and can bind before either of them does.
• Interest and corporate actions. The debit balance is treated here as fixed. Accrued margin interest raises it over time, and dividends, splits and distributions change both sides of the calculation.
• The short-side per-share floor. Rule 4210(c)(3) addresses stock ‘short’ in the account selling at $5.00 per share or above, and between $5.00 and $16.67 the $5.00 per share term in it exceeds 30 percent of market value. The 15.38 percent figure does not carry down into that range.

Concrete Framework

1. Write the debit, not the deposit, on the position record. The deposit is a starting equity figure. The debit balance is the number that stays constant and drives the trigger price.
2. Ask the broker for the house maintenance rate on that specific security before entry. The answer is a percentage, and it is often not 25. Record it with the position.
3. Compute the trigger price at entry, not during the drawdown. For a long financed at the Regulation T minimum, divide the debit by the number of shares and by one minus the maintenance rate. For the worked example, $5,000 divided by 200 and by 0.75 is $33.33.
4. Compute the short trigger separately. Multiply the entry price by 1.50 and divide by one plus the maintenance rate. At 30 percent that is $57.69 on a $50.00 short, a 15.38 percent move rather than a 33.33 percent one.
5. Compare the trigger price with the stop, and keep the stop inside it. A stop placed below the maintenance trigger hands the exit decision to the margin department. In the worked example a stop at $30.00 sits past the line at $33.33.
6. Re-run the numbers after every added share and every partial sale. Adding to a losing position changes the debit and the share count together, and the new trigger price is rarely where an eyeball estimate puts it.
7. Treat the FINRA series as context, not as a signal. It is a month-end total submitted under Rule 4521(d) and published with a lag. It carries no information about how close any individual account sits to its own line.

This article reads published rule text and one published data series. It is not investment advice and recommends no security or strategy. Prices, percentages and dollar figures other than the reported FINRA totals are this article’s calculations; margin rules are amended and broker house requirements change without notice, so re-check them against the current text of 12 CFR 220.12 and FINRA Rule 4210 and against the broker’s own schedule before use.