Position Sizing: Van Tharp's Golden Rule

The one variable that separates traders who survive from traders who blow up

You can have the best strategy in the world. Positive expectancy. A proven edge. Years of backtested data.

And still blow up your account in a month.

How? By ignoring the one variable that matters more than any other.

Position sizing.

Van Tharp spent decades coaching professional traders, and he came back to this point relentlessly: most traders obsess over entries, stress about exits, and completely neglect the question that actually determines their fate.

How much should I risk on this trade?

Get that wrong, and nothing else matters.

Why Position Sizing Is the "Golden Rule"

Here's what Tharp discovered after working with thousands of traders: the system you trade matters far less than how you size your positions within that system.

Two traders can use the exact same strategy. Same entries. Same exits. Same expectancy. One makes money. The other goes broke.

The difference? Position sizing.

Think about it this way. Your strategy determines your edge. But position sizing determines whether you survive long enough for that edge to play out.

A positive expectancy means nothing if you blow up before the law of large numbers kicks in. And the law of large numbers requires one thing above all else: staying in the game.

That's what position sizing protects. Your ability to keep playing.

The Math of Survival

Let's say you have a strategy with 50% win rate and a 2:1 reward to risk ratio. Solid edge. Positive expectancy.

But you decide to risk 25% of your account on each trade. What happens?

Four consecutive losses (which will happen eventually with a 50% win rate) and you've lost 100% of your capital. Game over.

Now imagine the same strategy, but you risk 2% per trade. Those same four consecutive losses cost you roughly 8% of your account. Painful, but survivable. You're still in the game. Your edge has time to work.

This is the math of survival. And it's not optional.

The traders who last decades in this business understand something the rest miss: the goal isn't to maximize returns on any single trade. The goal is to stay solvent through inevitable drawdowns so your edge can compound over time.

Position sizing is how you do that.

The 1% and 2% Rules

The most common position sizing approach is the fixed percentage risk model. Simple to understand, easy to implement.

Here's how it works:

The 1% Rule: Never risk more than 1% of your total account on any single trade.

The 2% Rule: Never risk more than 2% of your total account on any single trade.

If you have a $50,000 account and follow the 2% rule, your maximum risk per trade is $1,000. Period. Regardless of how confident you feel. Regardless of how "obvious" the setup looks.

For options traders, this means calculating your maximum loss before you enter. On a credit spread, it's the width of the strikes minus the premium received. On a cash-secured put, it's the strike price minus the premium (times 100). On a LEAPS position, it's typically the entire premium paid.

Once you know your maximum loss, you size the position so that loss equals 1% or 2% of your account.

Why Most Traders Ignore This

If position sizing is so important, why do most traders get it wrong?

Because it feels boring. Because it limits upside. Because when you're confident in a trade, risking "only" 2% feels like leaving money on the table.

And because the human brain is terrible at understanding low-probability, high-impact events.

We think, "What are the odds I'll hit five losers in a row?" And then we size up. And then variance does what variance always does.

Tharp called this the "anti-martingale" principle. In gambling, a martingale strategy means doubling down after losses. It feels intuitive but leads to ruin. The anti-martingale approach means sizing based on a fixed percentage of your current capital, which naturally reduces position size after losses and increases it after wins.

This is how you stay in the game.

Position Sizing for Options Sellers

If you sell premium, position sizing takes on extra importance. Here's why.

Credit spreads, iron condors, and cash-secured puts have defined maximum losses. That's the good news. You know exactly how much you can lose before you enter the trade.

The bad news? Those maximum losses can be multiples of your expected gain. A put spread that collects $100 in premium might have $400 at risk. That's a 4:1 risk to reward ratio.

If you're following the 2% rule on a $50,000 account, that $400 maximum loss means you can trade one contract. Not five. Not ten. One.

This feels limiting. But it's exactly what keeps you in the game when that spread goes against you.

The math works like this:

• Account size: $50,000

• Maximum risk per trade (2%): $1,000

• Maximum loss on trade: $400 per contract

• Position size: 2 contracts maximum

Most traders look at a high-probability spread and think, "I should load up. This is practically free money." And then they put on ten contracts. And then the market gaps through their short strike. And then they're down 20% in a single trade.

Position sizing prevents this. Not because it guarantees wins, but because it guarantees survival.

The Psychological Benefit

Here's something Tharp emphasized that most traders miss: proper position sizing does more than protect your capital. It protects your psychology.

When you know a single loss can only cost you 1% or 2%, you stop sweating every tick. You stop revenge trading. You stop making emotional decisions.

You trade your system instead of trading your fear.

This is the hidden benefit of conservative position sizing. It creates the mental space for good decision-making. When a trade goes against you, you can evaluate it rationally because the outcome isn't catastrophic.

Compare that to the trader who put 10% of their account on a "sure thing." Every price movement feels like life or death. And when the trade starts going wrong, panic sets in. They exit too early or too late. They double down out of desperation. They make every mistake in the book.

All because they sized wrong from the beginning.

Adjusting for Correlation

One more nuance that experienced traders understand: position sizing isn't just about individual trades. It's about portfolio risk.

If you have five positions all in tech stocks, you don't really have five independent 2% risks. You have one correlated 10% risk. When tech sells off, everything moves together.

The same applies to options strategies. Five put spreads on five different stocks might look diversified. But if they're all bullish positions and the market tanks, they all lose together.

Tharp's solution: think in terms of portfolio heat. How much of your total capital is at risk across all open positions?

A conservative rule of thumb: never have more than 6% to 10% of your capital at risk at any one time, across all positions combined. This forces you to be selective. You can't put on every trade that looks good. You have to choose the best setups and size them appropriately.

Implementation: Your Position Sizing Framework

Here's a simple framework you can implement today:

Step 1: Define your risk percentage. Start with 1% if you're newer or trading a smaller account. Move to 2% once you have confidence in your system and your discipline.

Step 2: Calculate your dollar risk. Multiply your account size by your risk percentage. That's your maximum loss per trade.

Step 3: Know your trade's maximum loss. For defined-risk options strategies, this is straightforward. For undefined-risk strategies, define a stop loss level and calculate the loss at that point.

Step 4: Size accordingly. Divide your dollar risk by your maximum loss per contract. Round down. That's your position size.

Step 5: Track your portfolio heat. Add up the maximum loss across all open positions. Stay below 6% to 10% of total capital.

Write this down. Put it next to your trading screen. Follow it every single time.

The Bottom Line

Van Tharp said it best: position sizing is the part of your trading system that determines how much you trade.

It's not glamorous. It won't help you find better entries or pick winning stocks. But it will keep you in the game long enough for your edge to matter.

Most traders who fail don't fail because they picked the wrong strategy. They fail because they sized wrong and blew up before their edge could work.

Don't be that trader.

Risk 1% to 2% per trade. Keep your portfolio heat under control. Trade like you plan to be doing this for the next twenty years.

Because if you size correctly, you will be.

Andy Crowder

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This newsletter is for educational purposes only and should not be considered investment advice. Options trading involves significant risk and is not suitable for all investors. Past performance does not guarantee future results. Always consult with a qualified financial professional before making investment decisions.