Position Sizing and the 1% Rule

The 1% rule is the most quoted and least understood rule in retail trading. It does not cap the size of your position. It caps what a position is allowed to cost you when it is wrong. That distinction is the whole lesson, and the arithmetic that follows from it takes about two minutes to learn.

What “risk per trade” actually means

The rule is usually stated as: never risk more than 1% of your account on a single trade. The trouble starts with the word risk, because three different numbers compete to be it.

It is not notional value. Notional is the face value of what you control: a 0.2-lot position in EUR/USD controls 20,000 units of the base currency. That number tells you the size of the exposure, not the size of the loss.

It is not margin. Margin is the deposit your broker holds while the position is open. It is a funding requirement set by leverage, and it moves when leverage changes even though nothing about the trade itself has changed.

Risk per trade is the distance to your stop, multiplied by your size. It is the amount of money that leaves the account if the trade goes exactly as badly as you already decided it was allowed to. Two inputs, one output. Nothing else enters the calculation.

Which means the rule has a direction of travel that most people get backwards. You do not choose a position size and then find out what it risks. You choose the risk first (1% of the account), then decide where the stop belongs based on the chart, and the position size is whatever number makes those two agree. Size is the output. Risk is the input.

Why a fraction survives what a fixed amount does not

The 1% rule is a specific case of what risk managers call fixed-fractional sizing: risk a constant percentage of current equity rather than a constant amount of money. The difference looks cosmetic on trade one and structural by trade fifty.

Take an illustrative 10,000 account and an illustrative losing streak. Every number in this section is arithmetic on assumptions, not a result of any strategy.

• Fixed amount. Risk 100 every trade regardless of balance. Twenty consecutive losses cost 20 × 100 = 2,000. The account sits at 8,000, down 20%.
• Fixed fraction. Risk 1% of whatever the balance currently is. Each loss multiplies equity by 0.99, so twenty losses leave 10,000 × 0.99²⁰, which is about 8,179, down roughly 18.2%.

A difference of 179 after twenty straight losses is not the point. The point is what the two curves do when the streak keeps going. After fifty consecutive losses the fixed-amount account is at 10,000 − 5,000 = 5,000, while the fixed-fractional account is at 10,000 × 0.99⁵⁰, about 6,050. After one hundred, the fixed-amount account is at zero by construction, and the fixed-fractional account is at 10,000 × 0.99¹⁰⁰, about 3,660.

In arithmetic, a fixed fraction shrinks forever and never reaches zero. A fixed amount has a countable number of losses in it, and you can work out that number on the day you open the account.

In a live account that arithmetic has a floor. Brokers enforce a minimum trade size, commonly 0.01 lots, so below a certain equity the fraction can no longer be scaled down and starts behaving like a fixed amount again, and a gap or slippage can carry a loss past the stop it was sized against. The property is a strong structural advantage, not a guarantee.

The fraction has a second, quieter property. Because the fraction is taken from current equity, size falls automatically while you are losing and rises automatically while you are recovering. The rule de-risks in the drawdown without you having to be brave enough to de-risk in the drawdown.

That 18.2% loss still needs about 22.3% of gains to return to 10,000, because 10,000 divided by 8,179 is 1.223. The asymmetry between what you lose and what you must make back is exactly why the fraction is kept small, and it is worked through in The Recovery Math: Why a 50% Loss Needs a 100% Gain.

The calculation, worked through

Here is the standard case, with the pip-value convention stated up front so every step can be checked.

Convention used: a EUR/USD account denominated in USD, where one pip is 0.0001 of quoted price and one standard lot is 100,000 units of the base currency. Pip value per standard lot is therefore 100,000 × 0.0001 = 10 USD per pip. This clean figure holds because the quote currency (USD) is also the account currency; for pairs quoted in another currency, the pip value must be converted at the prevailing rate. MetaTrader 5 reports margin, profit and loss in your account currency automatically, but it does not display pip value in the order window; that is a calculation you make yourself or add a tool for.

The inputs (illustrative): a 10,000 USD account, a 1% risk rule, and a trade idea whose invalidation level sits 50 pips from entry.

• Step 1: the risk budget. 1% of 10,000 = 100 USD. That is the most this trade may cost.
• Step 2: the cost of the stop at one standard lot. 50 pips × 10 USD per pip = 500 USD.
• Step 3: the size. Budget divided by cost per lot: 100 ÷ 500 = 0.2 lots.
• Step 4: check it. 0.2 lots is 20,000 units, so the pip value is 20,000 × 0.0001 = 2 USD per pip. A 50-pip stop at 2 USD per pip is 100 USD. The budget is met exactly.

Now change one input and watch what moves. Same account, same 1% rule, but the invalidation level is only 25 pips away. The stop now costs 25 × 10 = 250 USD per standard lot, so the size becomes 100 ÷ 250 = 0.4 lots. Checking it: 0.4 lots is 40,000 units, or 4 USD per pip, and 25 pips × 4 = 100 USD.

The position doubled. The risk did not move at all. This is the mechanism the rule exists to enforce: a tighter stop earns a larger position, a wider stop demands a smaller one, and the amount at stake stays constant while everything else flexes.

It also shows why notional and margin are the wrong anchors. At an illustrative rate of 1.1000, the 0.2-lot position carries 20,000 × 1.10 = 22,000 USD of notional exposure and the 0.4-lot position carries 44,000: 2.2 times and 4.4 times the account respectively. One carries double the exposure of the other, and they carry identical risk. Margin tells you even less: that same 22,000 of notional requires about 733 USD of margin at 1:30 leverage and 44 USD at 1:500, and in both cases the trade risks 100 USD. Leverage changed what the broker holds. It changed nothing about what the trade can cost you.

What changes if you are a copy-trading follower

If you follow a strategy rather than trade it, the four-step calculation above is not yours to make. You do not choose the entry, you do not place the stop, and you do not set the lot size; the strategy does, and a copier replicates it into your account, typically scaled by the ratio between your equity and the strategy account’s. When the strategy risks a fixed fraction of its own equity, your account inherits the same fraction of yours. The rule is being applied; you are just not the one applying it.

So the follower’s lever is not the trade. It is the allocation: how much capital sits behind that strategy in the first place. Allocation is the follower’s version of position sizing, and it is the only sizing decision you actually control.

The arithmetic is the same shape, one level up. Instead of asking “what does the stop cost me,” you ask “what does this strategy’s worst historical stretch cost me at this allocation.” Illustratively: if a strategy’s deepest recorded drawdown on its verified record is 20%, then 5,000 allocated to it corresponds to 5,000 × 0.20 = 1,000 of open loss at a repeat of that same event. Whether 1,000 is tolerable is a question you can answer calmly in advance, which is the entire benefit of asking it in advance.

Two honest caveats on that number. A historical maximum drawdown is a record of what has happened, not a ceiling on what can happen; a future stretch can be deeper. And it is only meaningful if it comes from a third-party-verified record such as a Myfxbook account rather than a screenshot, because an unverified drawdown figure is a marketing input, not a risk input. What a drawdown figure is really telling you is covered in Why Drawdown, Not Return, Defines a Strategy, and how to split capital across more than one strategy is a separate question again, handled in Copy-Trading Allocation: How Much to Put Behind Each Strategy.

Three ways the calculation goes wrong

• Sizing off leverage. “My account is 1:500, so I can take five times the position” treats a funding permission as a risk instruction. Leverage sets what you are allowed to open. It has no opinion on what you should. If your size changes when your leverage changes and your stop distance did not move, you are not running a 1% rule.
• Sizing off margin. Free margin is a liquidity number: it tells you whether the platform will accept the order, not whether the order is sensible. Sizing until margin runs out is how an account discovers its stop-out level experimentally.
• Sizing off feel. Adding size because the last three trades won, or because this setup “looks like the good one,” converts a rule into a mood. Whatever edge the method has is measured across all its trades taken at consistent size; varying the size by conviction quietly re-weights the sample toward the trades you were most confident about, which is not the same set as the trades that pay.

Key takeaways

• Risk per trade is stop distance multiplied by position size, not notional, not margin.
• Choose the risk first and the stop second; position size is what the arithmetic returns.
• A fixed fraction of current equity shrinks with the account; a fixed amount does not, and runs out after a countable number of losses. Your broker’s minimum trade size puts a floor under how far the fraction can scale down.
• Halving the stop distance doubles the position and leaves the risk unchanged. That is the rule working, not the rule breaking.
• As a follower, allocation is your position sizing. Size it against a verified drawdown profile, and accept that the profile is history, not a limit.

This article is educational and is not investment advice, a recommendation, or an offer. Every figure above (account balances, stop distances, pip values, lot sizes, leverage ratios, drawdown percentages and losing streaks) is illustrative and used solely to demonstrate the arithmetic; none are results, projections, or typical outcomes. Trading foreign exchange and CFDs carries a substantial risk of loss, including the loss of your entire investment. Disciplined position sizing manages exposure; it does not remove market risk, and past performance is not a guarantee of future results. Consider your own circumstances and seek independent professional advice where appropriate.