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A standard lot of EUR/USD is 100,000 euros, roughly $108,000 at 1.08. Your broker isn't handing you that exposure out of generosity. At 1:30 leverage it wants about $3,600 of your own money set aside before the order goes through, which means a $2,000 account physically cannot open the trade. That's forex margin doing its job: stopping you from betting the whole account on a hunch.
Most traders only think about margin when it's already too late, usually somewhere around 3am with a position bleeding out and a notification flashing on the platform. Here's how it actually works, and how to keep it boring.
Margin is a deposit held against an open position. It is not a fee, not a commission, and it does not disappear when you close the trade. The moment your position is flat, the margin goes back into your free balance and becomes available for the next idea.
The closest everyday comparison is a rental deposit. You're controlling something worth more than your cash on hand, so the broker holds a slice of your account as collateral against the position going wrong. Lose more than you put up and the broker is the one exposed, which is why it takes the deposit first and asks questions later.
Because margin is collateral rather than a cost, it's easy to ignore. Nothing appears in your trade history, no line item eats into your profit. That invisibility is exactly why it catches people out.
Leverage is the ratio. Margin is the cash that ratio produces. They are two ways of saying one thing, which is why a broker offering 1:100 leverage is really saying "we want 1% of the position's value as collateral."
The maths is short: margin = (units × price) ÷ leverage. Ten thousand units of GBP/USD at 1.2700 is $12,700 of notional exposure, so at 1:100 you'd post $127. The same position at 1:30 needs $423, and at 1:500 it needs $25.
That single setting decides how much market you can control per dollar of equity, and it is the most abused dial on any trading platform. Our breakdown of how 1:100 leverage can build or break an account goes further into where high leverage stops being useful and starts being expensive.
Your platform shows three numbers that matter far more than your open profit. They update in real time, and any one of them can shut you down.
The total locked up across all open positions. Open a second trade and it isn't funded from a fresh pot; used margin is the sum of every requirement. Some brokers net opposing positions on the same pair, many don't, which is worth confirming before you hedge anything.
Equity minus used margin. This is the cash genuinely available to open new trades or absorb losses. When free margin nears zero, new orders get rejected and every further tick against you starts eating the margin itself.
Equity divided by used margin, expressed as a percentage. This is the number brokers watch. Below about 200% is thin, at 100% most platforms issue a margin call, and somewhere between 50% and 30% they begin closing positions automatically. The exact thresholds are in your client agreement, not in your head.
Take a $5,000 account on 1:100 leverage. Same pair, same entry, same 200-pip move against you. Only the size differs.
Identical analysis, opposite result. The only variable was position size relative to available margin. If you want to see how much a pip is really worth on a given position, a pip calculator that shows the value in your account currency removes the guesswork in about ten seconds.
Regulated brokers in the UK and EU cap retail leverage at 1:30 on major pairs, which is a 3.33% margin requirement. Minor currency pairs sit at 1:20, gold at 1:20, individual shares at 1:5 and crypto at 1:2. Offshore entities advertise 1:500 or 1:1000 on the same instruments. The trade looks identical on the chart, but the collateral is twenty times smaller and the distance to zero is twenty times shorter.
Brokers routinely increase margin ahead of elections, central bank decisions and long weekends, sometimes doubling it with a day's notice. Volatility clusters around session overlaps, which affects both your exposure and the cost of holding it, as covered in when the forex market actually pays you across the trading day. A position that felt comfortable on a quiet Tuesday can become a problem on a Friday afternoon.
Work backwards. Decide the cash you're willing to lose, decide the stop distance in pips, then divide. That gives a lot size, and the lot size gives a margin requirement you can check against equity in advance rather than discovering it live. A lot size calculator that starts from risk rather than from gut feel turns a vague intention into a number you can defend.
As a working rule, keep used margin under roughly 20% of equity on your total book. That leaves margin level above 500%, plenty of room for a normal drawdown, and free margin left over to average in or add a second idea without a panic decision.
Then do the practical test. Open a 0.01-lot position and watch the three numbers move as price moves. Used margin stays fixed, equity breathes with the market, and margin level swings in the opposite direction to your P&L. Ten minutes of watching that relationship teaches more than any article. Traders who blow up rarely do it because they misread a chart. They do it because their position was too large to survive being wrong for a week, and margin was the thing quietly telling them so the whole time.
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