Margin & Buying Power Calculator
Reg-T margin and buying power calculator: enter equity and margin rules to see your leverage, max shares, and the price that triggers a margin call.
Enter your account equity and the margin requirements. You get the buying power that equity unlocks, your leverage, how many shares you could hold at a given price, and the price that would trigger a margin call on a fully-margined long.填入你的账户净值与保证金要求，即可得到——该净值所释放的购买力、杠杆倍数、在给定价格下可持有的股数，以及在满仓做多时触发追加保证金通知的价格。
Fill in equity and the margin requirements to see your buying power.填入净值与保证金要求即可查看购买力。
- Leverage杠杆
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- Max shares at entry入场价可持股数
- Position value仓位价值
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- Margin-call price追缴价格
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Your buying power is your account equity divided by the initial margin requirement — at Reg-T’s 50%, $10,000 of equity controls $20,000 of stock, or 2:1 leverage. That extra reach cuts both ways: the same move that doubles your gain also doubles your loss, and a big enough loss triggers a margin call that can force you to sell at exactly the wrong moment.你的购买力等于账户净值除以初始保证金要求——在 Reg-T 的 50% 下，$10,000 净值可操控 $20,000 的股票，即 2:1 杠杆。这份额外的操控力是双刃剑：让收益翻倍的那个波动，也会让亏损翻倍；而足够大的亏损会触发追加保证金通知，可能迫使你在最糟的时刻卖出。
01The formula公式
Leverage = 100 ÷ Initial margin%杠杆 = 100 ÷ 初始保证金%
Max shares = floor( Buying power ÷ Entry )可持股数 = 向下取整( 购买力 ÷ 入场价 )
Margin-call price = Entry × (1 − Init% ÷ 100) ÷ (1 − Maint% ÷ 100)追缴价格 = 入场价 × (1 − 初始% ÷ 100) ÷ (1 − 维持% ÷ 100)
The call-price formula assumes a fully-margined long — you borrowed the maximum the initial requirement allows, so your starting equity is exactly the initial margin on the position. As the price falls, your equity falls faster than the position value; the call fires the moment equity drops to the maintenance requirement.追缴价格公式假设满仓做多——你借入了初始保证金允许的上限，因此起始净值恰好等于该仓位的初始保证金。价格下跌时，你的净值下跌得比仓位价值更快；当净值降至维持保证金水平的那一刻，追缴便触发。
02A worked example一个算例
Suppose a trader has $10,000 of equity, a 50% initial requirement and a 25% maintenance requirement, and buys at $50.00.假设一位交易者有 $10,000 净值、50% 初始保证金要求、25% 维持保证金要求，并在 $50.00 入场。
- Buying power = 10,000 ÷ 0.50 = $20,000购买力 = 10,000 ÷ 0.50 = $20,000
- Leverage = 100 ÷ 50 = 2:1杠杆 = 100 ÷ 50 = 2:1
- Max shares = floor(20,000 ÷ 50) = 400可持股数 = 向下取整(20,000 ÷ 50) = 400
- Margin-call price = 50 × 0.50 ÷ 0.75 = $33.33 — a 33% drop wipes out the maintenance cushion.追缴价格 = 50 × 0.50 ÷ 0.75 = $33.33——约 33% 的跌幅即耗尽维持保证金的缓冲。
Notice the call comes long before the position is worthless: the stock only has to fall a third for the borrowed money to eat through the cushion. Without the loan, that same $50 stock at $33.33 would just be a paper loss you could wait out.注意追缴远在仓位归零之前就会到来：股价只需下跌三分之一，借来的钱便会吃穿缓冲。若没有借款，同一只 $50 的股票跌到 $33.33 只是一笔可以慢慢等待的账面浮亏。
03The common trap常见陷阱
Seeing $20,000 of buying power on $10,000 of equity tempts many traders to fill it — but every borrowed dollar carries interest and shrinks the distance to a margin call. Using the full 2:1 means a 25% drop in the stock can cut your equity in half and force a sale near the lows. Leverage is a tool for conviction, not a default setting; holding cash in reserve is what lets you survive the drop and add, rather than being forced out at it.在 $10,000 净值上看到 $20,000 购买力，会诱使许多交易者把它填满——但每一块借来的钱都要付利息，并缩短到追缴的距离。用满 2:1 意味着股价下跌 25% 就可能让净值腰斩，并在低点附近被迫卖出。杠杆是用于高把握时刻的工具，而非默认设置；留有现金储备，才能让你熬过下跌并加仓，而不是在低点被强平出局。
04Where this breaks它的局限
This math gives a clean Reg-T snapshot for a single long. Real accounts carry frictions it does not model. A few honest limits:这套算法为单笔做多给出干净的 Reg-T 快照，但真实账户还有它未纳入模型的种种摩擦。几点诚实的局限：
- Broker house rules. Brokers may set maintenance requirements well above the 25% regulatory floor — often 30–40%, higher still for volatile or concentrated names. Your real call price can be closer than this tool shows.券商自定规则。券商可将维持保证金要求设得远高于 25% 的监管下限——通常 30–40%，对波动大或高度集中的标的更高。你真实的追缴价格可能比本工具显示的更近。
- Margin interest and pattern-day rules. Borrowed cash accrues interest daily, and accounts under $25,000 face pattern-day-trading limits. Neither shows up in the buying-power number.保证金利息与日内交易规则。借入的现金按日计息，且低于 $25,000 的账户还受日内交易（PDT）限制。这两者都不会体现在购买力数字里。
- Gaps beat the call price. A margin call assumes the price passes smoothly through the trigger. An overnight gap can open below it, so the forced liquidation fills lower than the call price and the loss runs deeper than the math suggests.跳空会击穿追缴价。追缴计算假设价格平滑地穿过触发点。而隔夜跳空可能直接低开于该价位之下，强制平仓的成交价因此低于追缴价，亏损也比公式所示更深。
Buying power is borrowed reach, not extra capital — leverage multiplies the loss and the loss is what brings the call.购买力是借来的操控范围，而非额外的资本——杠杆会放大亏损，而正是亏损引来追缴。
Size a leveraged trade off risk with the 用 position size calculator仓位计算器, or go deeper in the lesson on 为杠杆交易按风险定仓，或在这节课中深入了解 position sizing仓位管理.。