How to size a stock trade without blowing up
A short, direct guide to the math that keeps traders in the game long enough for skill to matter.
Most retail traders do not fail because their market read is always wrong. They fail because position sizing is reckless. Buying a hot ticker without a defined stop and a defined account risk is how accounts disappear in a few bad weeks. The fix is not glamorous. It is arithmetic.
The 1% rule
Risk no more than 1% of your account on a single trade. On a $10,000 account, that means a maximum planned loss of $100. Some traders run 0.5%. Others push to 2%. The exact number matters less than the discipline: cap the downside, survive the streaks, and keep enough capital for the next setup.
The position-sizing formula
Once you know your dollar risk, the rest is straightforward:
- Position size = (Account x Risk %) / (Entry - Stop)
- Account: $10,000. Risk: 1% = $100. Entry: $50. Stop: $48.
- Position size = $100 / $2 = 50 shares.
If the trade stops out, the damage is controlled. If it works, the payoff depends on the quality of your exit plan, not on luck or oversized conviction.
Risk-reward is the other half
Position sizing protects you when you are wrong. Risk-reward determines whether being right pays enough to matter. A 1:2 setup means you can still break even with a lower win rate than most traders expect. A 1:3 setup gives you even more room for mistakes. Chasing trades below 1:1 is a hard way to survive.
Compounding is the real edge
A modest annual return can become meaningful over time if the account stays alive and contributions stay consistent. The compound calculator is there to make that visible. The point is not to trade more. The point is to avoid ruin and let repetition do the heavy lifting.
What these tools do not do
These calculators do not choose trades, predict direction, or replace your judgment. They remove arithmetic friction so you can think about the parts that matter: when to enter, where the idea is invalidated, and whether the expected reward justifies the risk.