The formula
required margin = (position size × price) ÷ leverage
A standard lot of EURUSD at 1.0850 has a notional value of $108,500. At 30:1 that requires $3,617 of margin; at 100:1, $1,085. The position is identical in both cases — the same pip value, the same profit and loss. Only the collateral differs.
Margin is not risk, and treating it as risk causes the damage
This is the sentence worth keeping: margin is returned when the position closes. It is not spent, not at risk, not lost. What you can lose is set entirely by where the stop sits.
The confusion runs in a costly direction. A trader who thinks of margin as risk concludes that lower leverage is safer, opens the same position at 30:1 instead of 100:1, and has changed nothing about their exposure — only tied up more collateral. Meanwhile a trader who understands that leverage does not create risk may take the opposite lesson and open a position four times larger because the margin permits it. That one does create risk, and it does so silently, because no single number on the platform went red.
Leverage is dangerous because it permits size. The size is what hurts you.
The number that actually matters: free margin
Required margin is easy. The useful figure is what is left.
Free margin is the buffer that absorbs open losses before the broker starts closing positions for you. When it runs out, the platform liquidates in its own order and at its own time, which is almost never the order or the time you would have chosen — and it happens while the account is already down, which is the worst moment to lose control of the exit.
So the question is not "can I open this" but "if this and everything else already open move against me together, at what point does the decision stop being mine". A position that locks up more than half the account as margin has effectively answered that question badly before the trade started, which is why the calculator raises it.
Where margin and the stop-out interact
Brokers express the danger zone as a margin level — equity divided by used margin, as a percentage. Typical thresholds are a margin call around 100% and a forced close somewhere between 20% and 50%, but they vary by broker and by regulator, so read yours rather than assuming.
Two positions with identical stops behave very differently here: the one opened at high leverage leaves a thicker free-margin cushion, so an adverse move reaches the stop before it reaches the stop-out. The one opened at minimum leverage may hit the broker's forced close first. That is the honest argument for not using the lowest available leverage on a small account, and it is close to the opposite of the usual advice.