Most retail traders who blow up did not blow up because their analysis was bad. They blew up because their position size was wrong for their conviction, their account, or their stop. The math to fix this is not complicated, and almost nobody who needs it has actually run it on their own account.
This is a short, practical walkthrough of the calculations that matter, written for traders who want to understand the inputs rather than just plug numbers into a calculator.
The single most important equation
For any trade, the dollar risk is:
dollar_risk = position_size × |entry_price - stop_price|
A long of 0.1 BTC at $61,000 with a stop at $59,500 carries a dollar risk of 0.1 × $1,500 = $150. That is the amount lost if the stop hits cleanly. (In practice it can be worse, because stops slip in fast markets, but $150 is the baseline.)
The mistake almost every beginner makes is calculating position size from the asset price ("I want to buy 0.1 BTC") instead of from the dollar risk ("I want to lose at most $150 if I am wrong"). Reversing this changes everything.
The 1% rule, properly stated
The most-quoted rule in trading is "risk 1% per trade." This is good advice that is usually applied incorrectly. The full statement is:
Risk no more than 1% of total account equity on any single trade, where "risk" is the dollar distance between entry and stop, not the notional position size.
A trader with a $10,000 account using 1% sizing has $100 of risk per trade. If the stop is 2% below entry, the position can be $5,000 ($100 / 0.02). If the stop is 0.5% below entry, the position can be $20,000. Same risk, very different position sizes, dictated by where the stop is.
This is why traders who pre-define their stop end up with rational sizing automatically, and traders who pick a position size first and then "decide where to stop out later" end up with risk that varies wildly trade to trade.
Why 1% and not 2 or 5
The math behind the 1% number is about surviving losing streaks. Consider the probability of a streak of N consecutive losses:
| Win rate | Probability of 10 losses in a row |
|---|---|
| 50% | 0.098% (1 in 1,024) |
| 60% | 0.010% (1 in 9,766) |
| 40% | 0.605% (1 in 165) |
Even at a 60% win rate, a 10-loss streak happens roughly once every 10,000 trades. At a 40% win rate, it happens once every 165. At 200 trades a year, that is more than once a year.
A 10-loss streak at 1% risk per trade is a 9.6% drawdown (compounding works in the trader's favor on the way down too). At 2% risk per trade, the same streak is an 18.3% drawdown. At 5% per trade, it is 40.1%. The 5% trader is one ordinary bad streak away from being psychologically destroyed; the 1% trader can shrug it off and keep going.
The 1% number is not magic. It is the largest size at which a normal losing streak does not derail traders emotionally or financially.
Adjusting for conviction (carefully)
Many traders use variable sizing: more on high-conviction setups, less on low-conviction ones. This is fine in principle and dangerous in practice.
The danger is that "conviction" is mostly post-hoc rationalization. Almost every trade feels high-conviction at the moment it is taken. Traders who scale up "when they are sure" usually end up scaling up randomly, just before the inevitable losing streak that happens at exactly the size that hurts the most.
For variable sizing to work, three things are needed:
- A written rubric for what makes a trade A-tier vs B-tier vs C-tier. Written before the trade. Not adjustable based on how the trader feels.
- A hard cap on the maximum size, no matter how high-conviction. Many disciplined discretionary traders cap at 2x their baseline.
- A retrospective check every month: did A-tier trades actually outperform B-tier trades? If not, the rubric is wrong and the trader should go back to flat sizing.
Most traders should run flat 1% sizing for at least their first 200 trades. The reason is not that flat sizing is optimal; it is that flat sizing protects against bad self-assessment until there is enough data to prove the rubric works.
The leverage trap
Crypto perpetuals make this all worse by inviting traders to use leverage. Leverage does not change the math above; it just changes which number blows up first.
The right way to think about leverage: it sets the maximum position size collateral can support, but actual position size should still be determined by dollar risk. Using 10x leverage on a $1,000 account does not mean a $10,000 position is appropriate. It means a $10,000 position is possible if the dollar risk calculation says so, and probably the actual position should be much smaller.
The trader who uses leverage to amplify position size beyond what dollar risk would dictate is the trader who gets liquidated, often by a wick that the exchange's liquidation engine catches before any human would have closed the position manually.
Practicing the math
This is the kind of thing that should be drilled on paper before it is done live. A few exercises:
- Open a paper trading account with $10,000 virtual. Set a hard rule: 1% risk per trade.
- Take 20 trades. After each, compute the dollar risk before submitting the order and write it in a journal. Refuse any trade where the size cannot fit into 1%.
- After 20 trades, look at the spread of position sizes. They should vary widely (because stop distances vary), but dollar risk should be near-constant.
- Then do 20 more trades that intentionally violate the rule, sizing by "what feels right." Compare drawdowns.
Hex37's position-sizer panel computes the dollar risk inline as order parameters are adjusted, which tends to make the discipline stick faster than doing the math separately in a spreadsheet. Any platform that surfaces dollar risk before submission works; the point is the habit, not the tool.
Bottom line
If there is one thing to remember: size trades by dollar risk, not by asset price or by "what feels right." Use 1% of account as the default. Pre-define the stop before entry so the calculation is honest.
This is, by a wide margin, the highest-leverage change a developing trader can make to their results. It also requires zero predictive skill. It is just arithmetic, applied honestly.
Hex37 is a paper trading platform with a built-in position sizer that computes dollar risk inline as order parameters are set. Free $10K virtual balance, realistic execution. hex37.com.