Position size

What Is Position Sizing?

Position sizing is the deliberate calculation of how many shares, contracts, or lots you purchase on a single trade. It can be determined in different ways, all acceptable depending on strategy. It is NOT based on how "confident" you feel about a chart pattern. It is NOT based on a tip you heard on TV. Proper position sizing can involve different independent factors depending on your chosen plan, strategy and style.

1. Account based: ($ or %): Share size based on the maximum amount of

   capital you are willing to lose if the trade fails.

   
   

2. Trade based: (Technical Stop-Loss): Share size based on the distance

   between your entry price and the price level that invalidates your trade idea.

   
   

3. Volatility-based: Sizing off a stock's ATR (average true range) rather than a flat share count, so a $200 volatile name and a $40 quiet one carry

   comparable dollar risk.

Here is an example. This is a ‘radar screen’ from my trading platform. The column ‘@Share size’ is the suggested opening share size based on share price. The ‘Probability of Profit’ column is calculated based on Average True Range combined with share price.

Scaling In: Starting Small and Building Into Strength

One approach worth taking seriously is entering a trade with a fraction of your intended size and adding to it only as price action confirms your thesis, rather than putting on a full position all at once. This is the system famously used by Jesse Livermore.

Why it works

No entry signal is certain — it's a probability, not a fact. Scaling in treats it that way. You pay a small "tuition" to test the idea with a starter position. If the trade confirms — a breakout holds, a pullback finds support, momentum continues in your direction — you add size into strength, effectively letting the market pay for the privilege of a bigger position. If it doesn't confirm, your loss on the starter size is a fraction of what a full-size entry would have cost, and you're often stopped out or scratch the trade before ever reaching full exposure.

This also does something for trading psychology that's easy to underrate: a small starter position keeps you calm enough to read price action objectively. Traders who go full size immediately tend to make decisions from fear rather than analysis, because the dollar swings are large enough to hijack judgment. A smaller initial stake lets you act like an analyst on the first leg of the trade instead of a gambler.

What NOT to do

Scaling in is not the same as averaging down. It is the opposite. Adding to a starter position because price is confirming your thesis is disciplined. Adding to a starter position because it's now underwater and you want a better average price is a different behavior wearing the same clothes — and it's how small losses become account-threatening ones. The distinction has to be mechanical, not a feeling in the moment:

· Add only above/below a level that would have triggered a fresh entry on its own— not simply because price is closer to your stop.

· Predefine your add levels and your total position cap before you enter, not while you're in the trade and emotionally invested in being right.

· Never let an add increase your risk beyond what you'd accept as a single, full-size trade. The point of scaling in is to reduce the risk of being wrong early — not to let you eventually take a larger position than your risk plan allows.

· Tighten the stop on the whole position as you add, so your risk on the initial shares/contracts is protected by the fact that the trade has moved in your favor.

NOTE: I prefer not to use physical stops. If you use them, that's fine. But if you trade using this system, you will be moving your stop constantly. Thing is, If you trade on a chart and the chart shows your current average price of entry, then the adjustment happens automatically. The average entry price will move closer to the current instrument price on the chart. This gives you a constant reference and a clear level to exit to either take profit or avoid a loss.

Where it costs you

Scaling in isn't free. If you nail the initial entry and the move happens fast, you'll make less on that trade than if you'd been full size from the start — you're deliberately trading some upside for a lower probability of a full-size loss. That's a legitimate trade-off, not a flaw, but it should be a conscious one. It also adds complexity: more decisions mid-trade means more opportunities for the plan to erode under pressure. It tends to suit traders with a clear, rules-based add trigger far better than traders who are still developing a feel for their setups — for the latter, it can just become a slower way to overtrade.

A workable version of this in practice

There are a multitude of ways to practice scaling in. Set a profit level based on share price where you will scale in. If the price moves to this level, enter the trade with opening (or small) size. If it reverses right away, simply exit at or close to break even. If it continues to the next dollar level, scale up to your next round of shares. Continue this until you reach your max size. It is of course a good idea to validate the trade with another signal, such as the Moving Averages, VWAP, Pivots or other solid levels according to your overall strategy. I have also learned that instead of scaling in with the same size each time it is better to start slightly larger and scale smaller size as you go. This keeps the average price from jumping up to the instrument price too soon and stopping you out.

(It is always a plus to have a platform that gives you quick executions.)

Why Position Size Matters More Than Your Entry

Most new day traders obsess over entries. They hunt for the perfect setup, the cleanest breakout, the exact candle that confirms their thesis. Meanwhile, the single variable that determines whether they're still trading in a year — position size — gets an afterthought's worth of attention. That's backwards. A mediocre entry with disciplined sizing is survivable. A great entry with reckless sizing is a coin flip with your account. Position size isn't a detail you bolt onto a strategy after the fact; it's the mechanism that decides whether a string of losses is a bad week or the end of your trading career.

The Real Job of Position Sizing

Position sizing has one job: keep any single trade, or any realistic losing streak, from doing damage you can't recover from. That's it. It's not about maximizing the size of your winners — it's about controlling the downside so you're mathematically able to stay in the game long enough for your edge to show up.

This matters because even a genuinely profitable strategy loses money regularly. A system with a 60% win rate will still produce five, six, sometimes eight losers in a row over a long enough sample — that's not bad luck, that's basic probability. If a losing streak like that can take out 30–50% of your account, the strategy's long-run edge is irrelevant. You won't be around to collect it.

None of this requires predicting the market better. It requires being more honest about what you don't know at the moment you click the buy or sell button — and building a process that lets the trade prove itself before you're fully committed to it. That discipline, applied consistently, tends to matter more over a year of trading than any single entry signal ever will.

The Math of Survival

Trading math is unforgiving. When you lose capital, the percentage gain required just to get back to even scales exponentially:

Account Drawdown Gain Needed to Break Even

10% 11.1%

20% 25.0%

30% 42.8%

50% 100.0%

75% 300.0%

Finally:

The goal of a day trader on any single day is not to make a fortune; it is to protect capital so they can execute tomorrow. A defined edge gives you an advantage over hundreds of iterations, but proper position sizing and strategic scaling are what keep you in the game long enough to actually realize those gains.