Position sizing: how to calculate trade sizeTwo traders take the same trade, at the same price, with the same stop. One loses 1% of their account and the other loses 10%. The only difference between them is a number they chose before entering.Sizing one trade correctly is arithmetic. Keeping an account alive across a hundred of them is a different job, and it is mostly about the losing streak you have not had yet.

Risk management does not try to avoid losing trades. Losses are the cost of participating and no method removes them.
What it does is decide, in advance, how much any single trade and any single week can take out of the account. A good strategy with no risk framework will eventually meet the run of losses that ends it. A weak strategy with a perfect one just loses more slowly - risk management controls consequences, it does not create an edge.
How big should this position be is position sizing: risk amount divided by stop distance, in that order and not the other way round.
What relationship between risk and reward does the method need is risk and reward, and the short version is that win rate on its own tells you nothing.
Are these positions actually separate is diversification, and the answer is usually less than it looks.
This article is about what none of those cover: the account as a whole.
This is the arithmetic that makes the case for small positions better than any argument can. Losses and the gains needed to undo them are not the same size.
| Drawdown | Gain required to get back to level |
|---|---|
| 5% | 5.3% |
| 10% | 11.1% |
| 20% | 25.0% |
| 30% | 42.9% |
| 50% | 100.0% |
| 75% | 300.0% |
Lose half and you must double what remains simply to break even. Not double your original account: double the reduced one. This is why controlling the depth of a drawdown matters more than the speed of a recovery.
A strategy winning 60% of the time still loses 40% of the time, and across hundreds of trades those losses will cluster. Ten consecutive is unusual, not impossible, and the framework has to survive it.
A $10,000 account, ten straight losers
The differenceRecoverable, or notThe first account needs 10.6% to get back. The third needs 187%. Same strategy, same ten trades, same market. The only variable was position size.
Margin is what the broker requires to open the position. It has never been a limit on what you can lose.
Two figures from our hundred broker records that decide how bad the worst case can be.
The leverage figure is a ceiling, not an instruction. Nothing obliges you to use a hundredth of it, and [what is leverage](/insights/trading-basics/what-is-leverage/) covers why the maximum is the least interesting number on the page.
A broker offering 1:500 is describing a limit. What you are actually running is your exposure divided by your equity.
A $20,000 account holding a $40,000 position is at 2:1, whatever the broker permits. The same account holding $600,000 is at 30:1, and a 1% adverse move takes 30% of the account.
Nobody is ever forced into high effective leverage. It is chosen, usually gradually, by taking slightly larger positions during a good run.
A maximum daily loss - say 3% of the account - stops trading for the day once reached. A weekly version does the same over a longer window.
The purpose is not the arithmetic. Losing 3% is survivable; the framework already handles that. The purpose is to interrupt the sequence that follows a bad session, when the impulse is to make it back before the day closes.
That impulse produces bigger positions on worse setups, and it is how an ordinary bad day becomes the worst month of the year. A limit set in advance is a decision made by somebody who was not upset at the time.
Martingale-style approaches double the position after each loss on the reasoning that a winner eventually recovers everything. Here is what the ladder actually looks like from $100.
| Consecutive loss | Risk on the next trade |
|---|---|
| 1st | $100 |
| 2nd | $200 |
| 3rd | $400 |
| 4th | $800 |
| 5th | $1,600 |
| 6th | $3,200 |
| 7th | $6,400 |
By the seventh trade you are risking sixty-four times the original amount to recover $6,300 already lost. The strategy does not fail because the logic is wrong. It fails because capital and margin run out before the winning trade arrives.
Position sizing assumes the stop fills where you put it. Sometimes it does not, and the useful exercise is to ask what happens when several things go slightly wrong at once.
Five open positions, each risking 1% of a $20,000 account, is $1,000 of planned risk. Now assume a news event gaps the market, every stop slips, and the actual combined loss is $1,300. Is that survivable? Almost certainly.
Run the same exercise with five positions at 5% each and the answer changes completely. Planned risk of $5,000 becomes something closer to $6,500, which is a third of the account gone in a single session on trades that were all individually within the rules.
The first four are arithmetic. The last two are the ones that actually get skipped.
There is no universal figure. Limits of 0.5%, 1% or 2% of account equity are common. The relevant test is whether ten consecutive losses at that size leaves an account you can still work with.
No. It means the planned loss is about 1%. The position controlling that risk can be far larger, because the stop distance defines the loss rather than the position size does.
No. Margin is collateral required to hold the position. Losses are driven by position size and market movement.
Yes. Winning 40% of the time with winners twice the size of losers is profitable. Win rate alone is not a measure of anything.
Because you must double the remaining capital to get back to where you started, and the remaining capital is half of what it was.
Your actual exposure divided by your account equity. As distinct from the maximum the broker permits, which is just a ceiling.
Not if it is planned, with a defined maximum position and a defined exit. It becomes dangerous when it is improvised to avoid accepting a loss that was already planned for.
Moving it further away replaces the risk you accepted with a larger one you have not thought about. Moving it in your favour as a trade progresses is a different thing entirely: see trailing stops.
No. It controls how much a strategy can cost you. It cannot give one a positive expectancy it does not have.
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