Calculate the optimal number of shares to buy based on your portfolio size, risk tolerance, and stop-loss level. Never risk more than you can afford to lose.
Position sizing is the most important risk management tool in investing and trading. It determines how much money you put into each trade. The golden rule: never risk more than 1-2% of your total portfolio on a single trade. This ensures that even a string of losing trades won't destroy your portfolio.
Always aim for a risk:reward ratio of at least 1:2 — meaning your potential profit is at least twice your potential loss. A 1:3 ratio is even better. If you can't find a trade with at least 1:2, consider skipping it.
You have a $50,000 portfolio and want to risk 2% per trade ($1,000). You want to buy a stock at $150 with a stop-loss at $140 (risk of $10/share). Position size: $1,000 ÷ $10 = 100 shares ($15,000 position). If the stock hits your stop, you lose exactly $1,000 — 2% of your portfolio. Manageable.
Conservative investors: 0.5-1%. Active traders: 1-2%. Aggressive traders: 2-3%. Never exceed 5% risk per trade under any circumstances.
Position sizing applies to everyone. Even long-term investors should decide how much of their portfolio to allocate to each stock. The 5% rule (no single stock > 5-10% of portfolio) is the long-term equivalent.
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