Stock Basics · Lesson 6/7 · 5 min read
Risk Management Basics
Why "How Much Can I Lose" Comes Before "How Much Can I Make"
Most beginner investors only think about how much a stock might go up. Traders who survive long term ask the opposite question first: "If this trade is wrong, how much do I lose?" If you can't answer that question, you're not ready to place the trade yet.
Losses Require Disproportionately Larger Gains to Recover From
This is the most mathematically concrete reason risk management matters. The bigger your loss percentage, the disproportionately larger the gain you need just to get back to even.
| Loss | Gain needed to break even |
|---|---|
| -10% | +11.1% |
| -20% | +25% |
| -30% | +42.9% |
| -50% | +100% |
| -70% | +233% |
Lose 50% and you need your remaining money to exactly double just to get back to where you started. This is why keeping losses small matters far more for long-term survival than chasing spectacular gains.
Position Sizing: How Much to Risk on One Trade
Position sizing is about deciding how much of your total capital to put into a single trade. A widely used rule of thumb is "risk no more than 1–2% of your total account on any single trade."
Say you have $10,000 in capital and set your risk limit at 1% ($100). If your entry is $50 and your stop is $47 (6% below entry):
Loss per share = $50 - $47 = $3
Max shares = Risk limit ($100) ÷ Loss per share ($3) = 33 shares
Buying up to 33 shares means that even if you get stopped out, you only lose 1% of your account. Set a tighter stop (e.g., -3%) and you can buy more shares within the same risk limit; set a wider stop and you need to buy fewer. The key is sizing your position based on the distance to your stop — not just picking a round number of shares.
💡 Calculating position size this way keeps the impact of any single trade on your overall account roughly consistent, even across stocks with very different volatility.
Diversification: Don't Put All Your Eggs in One Basket
Putting all your capital into a single stock means that if unexpected bad news hits that one company (an accounting scandal, a lawsuit, an industry collapse), your entire account takes a major hit. Diversification is how you reduce this single-stock risk.
- Across stocks: Spread capital across multiple companies
- Across sectors: Spread across different industries — semiconductors, financials, healthcare, etc. (stocks in the same sector often get hit by the same bad news at the same time)
- Across time: Instead of buying all at once, buy in stages at different points in time (dollar-cost averaging)
⚠️ Over-diversifying makes a portfolio hard to manage and pulls your returns toward the market average. There's no single right number of positions, but most individual investors settle on a number they can realistically track and manage day to day — commonly somewhere in the 5–15 range.
Look at Your Total Risk Across All Open Positions Too
Even if you cap each individual trade's risk at 1%, holding 10 positions that are all in the same direction (say, all long) means the whole portfolio can take a large hit fast if the market moves sharply against that direction. So beyond per-trade risk, it's worth also setting rules at the account level:
- Total risk across all open positions combined
- How concentrated your positions are in one direction (long vs. short)
- A maximum daily loss limit
When Emotions Break Risk Management
Even a technically perfect set of risk rules gets broken in practice — and emotion is usually the biggest culprit.
- Loss aversion: Your stop level gets hit, but you tell yourself "it'll bounce back soon" and delay the exit.
- Revenge trading: Right after a loss, you re-enter aggressively and emotionally, trying to win it back immediately.
- Overconfidence: After a few wins in a row, you ignore your risk limits and size up.
The most effective way to guard against these patterns is to decide your rules before you trade, and follow them mechanically once you're in the trade. Deciding your stop, target, and position size before you enter dramatically reduces the room for emotion to creep in.
The Diversification Illusion: Correlation Risk
Spreading capital across 10 stocks doesn't automatically mean you're diversified. If all 10 are semiconductor stocks, you technically hold 10 positions, but you're really concentrated in a single risk: the semiconductor industry cycle. The degree to which different assets move together is called correlation, and grouping only highly correlated stocks together gives you more positions on paper but not much real diversification benefit.
Genuine diversification comes from mixing assets that normally move differently from one another. Spreading across sectors is one way to do this; going further and mixing entirely different asset classes — stocks and bonds, for instance — is another common approach.
A Caution About Position-Sizing Formulas: The Kelly Criterion
The most famous attempt to mathematically "optimize" position size is the Kelly Criterion.
Kelly fraction = Win rate - [(1 - Win rate) ÷ Risk/reward ratio]
Given your win rate and risk/reward ratio, this formula calculates "the betting fraction that grows your capital fastest over the long run." In practice, though, it has two traps:
- Win rate and risk/reward are estimates with no guarantee of holding steady in the future. Even a small estimation error can swing the Kelly-suggested fraction dramatically.
- The "optimal" fraction the Kelly Criterion suggests may be mathematically optimal, but the volatility along the way — the size of the drawdowns your account experiences — can be more than most people can actually stomach in practice.
This is why many traders in practice use half or a quarter of what the Kelly formula suggests ("half-Kelly," "quarter-Kelly"), or stick to a more conservative fixed approach like the "risk 1–2%" rule from this lesson. A formula existing doesn't automatically make it more precise or safer — keep that in mind.
Summary
- Bigger losses require disproportionately bigger gains to recover from, so avoiding large losses should be your top priority.
- Size your position based on "distance to your stop," typically capping risk at 1–2% of your total account per trade.
- Diversify across stocks, sectors, and time — and manage risk at the account level too, not just per trade.
- Deciding your rules before you trade is the single most reliable way to keep emotion from taking over in the moment.
Before we move into the Trading Strategies course, the next lesson rounds up the terms you'll run into there.