Position sizing before entry

Most traders size positions backwards. They decide how much to buy — based on conviction, excitement, or whatever number feels substantial — and then, if a stop occurs to them at all, they bolt one on afterwards. Risk-first sizing inverts the order: decide what you are willing to lose, find where the trade is wrong, and let those two numbers compute the size. The position size stops being a feeling and becomes arithmetic.

This inversion matters because of an asymmetry in what you control. You do not control whether the next trade wins; nobody does. You control exactly one variable completely: how much is at stake when it loses. Sizing is the entire interface between your account and the market’s randomness — which makes it strange that it gets a fraction of the attention lavished on entries.

The formula

Three inputs, one output. Account risk: the dollars you accept losing on this one trade — commonly 0.5% to 2% of the account, decided as policy, not per trade. Stop distance: the percentage from entry to stop, set by structure as covered in the stop-loss lesson. Size: account risk divided by stop distance. That is the whole machine: position size equals dollars risked divided by the fractional distance to the stop.

1. Fix your per-trade risk as a percentage of the account — say 1% of $10,000, so $100.
2. Place the stop where the trade thesis fails — say 5% below entry.
3. Divide: $100 of risk over a 5% stop gives a $2,000 position.
4. Sanity-check: if a $2,000 position falls 5%, the loss is $100. The math closes.

Worked examples across instruments

• A $50 stock, stop at $46. Risk per share is $4. With $100 of account risk: 25 shares, a $1,250 position. The stop is 8% away, and 8% of $1,250 is $100. Checks out.
• A coin at $2.00, stop at $1.84. Risk per unit is $0.16, so $100 buys you 625 units — again $1,250 of notional. Same risk, same size class, wildly different asset.
• A tight setup: stop 2% away. $100 over 2% is a $5,000 position — half the account in one trade, with a perfectly ordinary 1% risk. Tight stops permit large size; whether the account should carry that much in one instrument is a separate, fair question.
• A wide setup: stop 10% away. $100 over 10% is a $1,000 position. If that feels insultingly small, the message is not that the formula is broken — it is that this trade is expensive to be wrong about.

Notice what just happened across those examples: volatility regulated itself. The volatile coin with the distant stop got a small position; the quiet setup with the near stop got a large one. Risk-first sizing is a thermostat — every trade arrives at the same dollar risk regardless of how wild the underlying instrument is. This is also why the method travels across asset classes: the formula does not care whether the instrument is one of Obsidiate’s 15 forex pairs or a small-cap coin, only where the stop is.

Why size is the only lever you fully control

Entries depend on the market cooperating. Exits depend on fills, gaps, and liquidity. Win rate depends on conditions you cannot see. Size is the lone variable with no external dependency — the market has no vote in how much you put on. And it is the variable that determines survival: ten consecutive losses at 1% risk is a drawdown around 10%, irritating and recoverable; the same streak at 10% risk destroys close to two-thirds of the account, which then needs roughly a 170% gain just to break even. Losing streaks of that length are not bad luck — over enough trades they are a statistical certainty for every strategy. Sizing decides whether a normal streak is a bruise or an obituary.

The usual ways people break it

• Conviction sizing — tripling size because this one feels certain. Feelings are not inputs; the strongest convictions precede the most memorable losses.
• Revenge sizing — doubling after a loss to make it back quickly. This compounds risk precisely when judgment is most impaired.
• Stop widening after entry — moving the stop down converts your calculated risk into an uncalculated one; the original math is void the moment the stop moves.
• Correlation blindness — 1% risk on five coins that move together is one 5% bet wearing five costumes.
• Ignoring fees and slippage — at small risk numbers, a Bronze-tier round trip plus slippage can consume a meaningful slice of the planned risk; budget for it in volatile or thin instruments.

Key takeaways

• Decide dollars at risk first, find the invalidation point second, and let size be the output — never the input.
• The formula: position size equals account risk divided by stop distance as a fraction.
• Wider stops force smaller positions automatically; the method self-adjusts across calm and violent instruments alike.
• Size is the only trading variable the market cannot touch, and it alone decides whether a normal losing streak is survivable.
• If the computed size feels too small, the trade is too expensive to be wrong about — skip it rather than inflate it.
• Watch correlation: several full-risk positions in instruments that move together are one oversized bet.