Position Sizing Explained Simply: The Math That Keeps You in the Game

Most traders spend 90% of their time on entries and exits. They obsess over indicators, candlestick patterns, and the perfect entry signal. Then they risk half their account on a single trade and wonder what went wrong.

Position sizing is the skill that actually keeps you in the game. It does not matter how good your strategy is if one bad trade wipes out your capital. This guide breaks down exactly how to calculate your position size — in plain English, with real examples.

Why Position Size Matters More Than Your Entry

Here is a scenario that plays out every day:

Trader A has a 60% win rate with a great strategy. Risks 20% per trade.
Trader B has a 45% win rate with a decent strategy. Risks 1% per trade.

Who survives a 10-trade losing streak? Trader B, every time. Trader A is down 87% and likely done. Trader B is down less than 10% and still trading.

Your edge comes from your risk management, not your win rate. Position sizing is how you enforce that risk management on every single trade.

The math is not complicated. But most traders skip it entirely. Let's fix that.

The Core Formula

Position sizing comes down to answering one question: "How many shares, lots, or contracts should I buy?"

Here is the formula:

Position Size = (Account Balance × Risk %) ÷ Trade Risk Per Unit

That is it. Three numbers you already know:

Account Balance — how much money you have
Risk % — how much you are willing to lose on this trade (most pros use 0.5–2%)
Trade Risk Per Unit — the dollar distance between your entry price and your stop loss

Let's walk through real examples.

Example 1: Stock Trader

You have a $10,000 account. You want to risk 1% per trade. You are buying AAPL at $175 with a stop loss at $170.

Here is the calculation:

Account Balance: $10,000
Risk %: 1% = $100 max loss
Trade Risk Per Share: $175 − $170 = $5 per share

Position Size = $100 ÷ $5 = 20 shares

You buy 20 shares. Your total position is $3,500 ($175 × 20). If your stop loss hits, you lose exactly $100 — which is 1% of your account. No surprises.

What if you risked 10% instead?

Position Size = $1,000 ÷ $5 = 200 shares ($35,000 position)

Now a single trade puts $1,000 at risk. Five losing trades in a row — which happens to every trader — and you are down $5,000. Half your account. Gone.

Example 2: Forex Trader

Forex uses lots instead of shares. The math is the same, but you need to account for pip value.

You have a $5,000 account. You risk 1% = $50 max loss. You are trading EUR/USD. Entry at 1.0850, stop loss at 1.0800. That is a 50-pip stop.

Account Balance: $5,000
Risk %: 1% = $50
Stop Distance: 50 pips
Pip Value (for a mini lot): ~$1 per pip

Position Size = $50 ÷ (50 pips × $1) = 1 mini lot

If you traded a full standard lot ($10 per pip), your risk would be $500 — 10% of your account. One trade. Same setup. Massive difference in outcome.

The 1% Rule: Why Pros Swear By It

The 1% rule is simple: never risk more than 1% of your account on a single trade.

For a $10,000 account, that means a maximum loss of $100 per trade. For a $100,000 account, it is $1,000.

Why 1%?

Survival. Even a devastating 20-trade losing streak only costs you ~18% of your account. Recoverable.
Emotional control. When you know the most you can lose is small, you trade with a clear head.
Compounding. As your account grows, your position sizes grow automatically. As it shrinks, they shrink. Built-in protection.

Some experienced traders use 0.5% for extra safety or 2% when they have high conviction. But going above 2% on any single trade is gambling, not trading.

Common Position Sizing Mistakes

1. Risking a Fixed Dollar Amount Instead of a Percentage

"I always risk $500 per trade." This sounds disciplined, but it is dangerous. On a $50,000 account, $500 is 1%. On a $5,000 account, $500 is 10%. The risk percentage should be constant — the dollar amount should change as your account changes.

2. Ignoring Stop Loss Distance

A tighter stop loss lets you take a larger position. A wider stop loss forces a smaller position. Some traders use the same position size regardless of where their stop is — which means they are either risking too much or too little.

3. Moving Your Stop to "Give the Trade Room"

If you widen your stop after entry to avoid getting stopped out, your position size is now wrong. You are risking more than you planned. This is how small losses become big ones. Set your stop before entry. Size your position. Do not move the stop backward.

4. Not Accounting for Slippage and Spreads

Your actual exit might not be exactly at your stop price. Factor in slippage (especially in forex) and reduce your position size slightly to compensate. A $100 risk budget with $5 of slippage means you should really only risk $95 — size accordingly.

How to Track Your Position Sizing in Your Journal

Position sizing data is some of the most valuable information in your trading journal. Log these fields for every trade:

Account balance at entry
Risk percentage used
Position size (shares/lots)
Entry price and stop loss price
Actual dollar risk
Actual dollar result

After 50+ trades, review this data. You might discover:

You perform better with smaller position sizes (less emotional pressure)
Your biggest losses came from inconsistent sizing
Your best win streaks happened when you strictly followed the 1% rule

The numbers do not lie. Your trading journal is the tool that reveals them.

Quick Reference Table

Here is a cheat sheet for a $10,000 account at 1% risk ($100 max loss):

| Stop Distance | Shares to Buy | Total Position | |---|---|---| | $2 | 50 | $ varies by price | | $5 | 20 | $ varies by price | | $10 | 10 | $ varies by price | | $20 | 5 | $ varies by price |

The formula adapts to any account size and any stop distance. Plug in your numbers and trade with confidence.

A Simple Routine Before Every Trade

Before you click buy or sell, run through this:

What is my account balance? Check it.
What percentage am I risking? Should be 0.5–2%.
Where is my stop loss? Know the exact price.
What is my position size? Calculate it using the formula.
Does the actual dollar risk match my plan? Verify.

This takes 30 seconds. It can save your account.

Final Thoughts

Position sizing is not glamorous. It does not show up in trading screenshots or highlight reels. But it is the single most important factor in whether you survive as a trader.

You do not need a complex spreadsheet. You do not need expensive tools. You need the formula, the discipline to use it, and a trading journal to track your results over time.

Start small. Risk 1%. Let your journal show you the data. As your account grows, your positions grow with it — automatically, safely, and sustainably.

Ready to track your position sizing and see the data for yourself? Start logging every trade with LogYourTrade — the trading journal that helps you trade smarter, not harder.