Risk & Position Sizing

Today’s read posts after the close.

Everything else on this site is about reading the market. This page is about the only part you actually control.

You do not control whether a position works. You control how much is at stake, where you are wrong, and whether you take the trade at all. That is a short list, and it is the whole list.

Size is a decision about survival, not about conviction

The most common and most expensive error in this whole subject is letting confidence set position size.

It feels rational. A better setup deserves more money. But confidence is not calibrated, especially not your own, and the trades that feel most certain are frequently the ones where you have stopped checking. Sizing off conviction means your largest losses arrive precisely when you were most sure, which is also when you are least prepared to accept them.

The alternative is arithmetic. Decide what a single position may cost you if it fails, as a fixed fraction of the account. Then let that number and the distance to your invalidation point determine the size. Wide invalidation, smaller position. Tight invalidation, larger one. Same risk either way.

The consequence is that size stops being an expression of opinion and becomes a consequence of structure. That feels worse and performs better.

The asymmetry nobody internalises early

Losses and gains are not symmetric, and the arithmetic is brutal enough to be worth stating in full.

Lose ten percent and you need about eleven percent to recover. Lose twenty and you need twenty-five. Lose fifty and you need one hundred. Lose seventy-five and you need three hundred percent, which in practice means the account is finished regardless of how good the next idea is.

Every large drawdown is a mathematical tax on all future returns. This is why capital preservation is not timidity, it is the precondition for compounding at all. The trader who avoids the catastrophic loss beats the trader with better ideas and one disaster, and it is not close.

Four dimensions, not one

Risk is usually taught as a stop level, which is one dimension of four.

How much per position, which is the sizing arithmetic above.

Where you are wrong, decided before entry and by the structure of the idea rather than by what you can emotionally tolerate. A stop placed where it will not hurt is placed where it means nothing.

How much across everything at once. Five positions in the same theme is one position with extra commission. Correlation collapses toward one exactly when things go badly, which is when the diversification you thought you had turns out to be decoration.

How much in a period. A daily or weekly loss limit that stops you trading is protection against the specific failure where a bad day becomes a bad week through revenge trading. This one is about behaviour rather than mathematics, and it is the one most people skip.

All four are developed in risk in four dimensions.

The trade you do not take

There is no rule requiring you to have a position. Cash is a position, and it is the correct one more often than the industry's incentives will ever admit to you.

Most of the damage I have seen, in my own record and in other people's, comes from trades taken because nothing better was available rather than because the setup was there. Boredom is not a signal. Neither is having recently lost money, and the trade taken to recover the last one is reliably the worst of the sequence.

The null trade is about this at length, and the discipline is genuinely harder than any analytical technique on this site.

Why this is where the honest record matters

Position sizing is where the compounding either happens or does not, and it is invisible in the way most trading is discussed. Nobody posts a screenshot of a position they sized correctly.

It is also where a scored record stops being marketing and becomes useful to you. Knowing your own hit rate, your distribution of outcomes, and how large your losses run relative to your gains is what makes sizing an informed decision rather than a guess dressed as a policy. Without that, a percentage rule is a number you picked because it sounded prudent.

That is the practical case for keeping a journal and for scoring your own calls: not discipline for its own sake, but because sizing without your own numbers is sizing blind.

What this page is not

It is not personalised advice, and nothing here is a recommendation. The right amount of risk for any individual depends on circumstances I do not know and cannot know.

It is also not a promise. Correct sizing does not make a strategy profitable. It makes a profitable strategy survivable and an unprofitable one slower to kill you, which is worth having but is not the same as an edge. Risk management is what keeps you in the game long enough to find out whether you have one.

The reason it comes first anyway is simple. Every other page here is about improving the quality of a decision. This one is about making sure a bad decision does not end the sequence.

Educational market analysis only. Not investment advice, not a recommendation, and not personalised to anyone's circumstances.

Questions traders ask

What is this Risk & Position Sizing page?

A dated, running read on risk & position sizing from a trading desk that scores its own calls publicly — hits and misses both.

How often is it updated?

After the market close on trading days.

Is this investment advice?

No — educational market analysis only. Nothing here is a recommendation.