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Position Sizing: How Much Should You Risk per Trade?

Position sizing sets how much to buy so a stopped-out trade loses only a fixed slice of your account: units = (account × risk %) ÷ (entry − stop).

By TradingDots Editorial 9 min read

US 100 dollar bills in front of a screen showing a rising price chart on a trading app
In this guide
  1. What Is Position Sizing?
  2. Position Size vs Risk: Two Different Numbers
  3. The Position Sizing Formula (Fixed Fractional Method)
  4. Position Sizing for Crypto
  5. Volatility-Based Position Sizing With ATR
  6. The Kelly Criterion and Why Traders Use a Fraction of It
  7. Position Size vs Leverage
  8. Common Position Sizing Mistakes
  9. Bottom Line
  10. Sources

Position sizing is the process of deciding how many shares, coins or contracts to buy so that, if your stop-loss is hit, you lose only a set amount, typically 0.5% to 2% of your account. Most traders use one formula: position size = (account × risk %) ÷ (entry price − stop price). With a $10,000 account, 1% risk and a $2 stop distance, that is $100 ÷ $2 = 50 shares.

Position sizing matters more than most beginners expect. Two traders can take the exact same trades and get very different outcomes simply because one bets 1% per trade and the other bets 15%. The first survives a losing streak; the second may not.

This guide explains the difference between position size and risk, walks through the formula for stocks and crypto with real numbers, shows volatility-based sizing with ATR, explains the Kelly criterion and why traders only use a fraction of it, and covers the mistakes that turn small losses into big ones. All examples are hypothetical and are not recommendations to trade any asset.

What Is Position Sizing?

Position sizing answers the question “how much should I buy?” for a specific trade. It is one part of a wider risk management plan, and it connects three numbers you should know before you enter any trade:

  • Account size: the equity in your trading account (your own money, not including margin you could borrow).
  • Risk per trade: the maximum you are willing to lose if the trade fails, usually stated as a percentage of the account. The common 1% rule caps it at 1%.
  • Stop distance: the gap between your entry price and your stop-loss, the price at which you will exit because the trade idea is wrong.

Fix any two of these and the third, the position size, is no longer a choice. It is a calculation. That is the whole idea: you decide the risk, the chart decides the stop, and arithmetic decides the size.

Position Size vs Risk: Two Different Numbers

Beginners often confuse the size of a position with the risk of the position. They are not the same.

  • Position size is how much money is in the trade: 100 shares at $50 is a $5,000 position.
  • Risk is how much you lose if the stop is hit: with a stop at $48, you lose $2 × 100 = $200.

A $5,000 position with a stop $1 away risks $100. A $1,000 position with no stop at all risks the full $1,000. Position size tells you exposure; the stop tells you risk. Good sizing keeps risk constant from trade to trade, which means position size will change every time. A trade with a tight stop gets a bigger position; a trade with a wide stop gets a smaller one.

Account Risk (1%) Entry Stop Stop distance Shares Position value
$10,000 $100 $50 $49 $1 100 $5,000
$10,000 $100 $50 $48 $2 50 $2,500
$10,000 $100 $50 $45 $5 20 $1,000
$10,000 $100 $50 $40 $10 10 $500

In every row, the loss at the stop is $100. That is what consistent risk looks like.

The Position Sizing Formula (Fixed Fractional Method)

The most widely used method is fixed fractional sizing: you risk the same fraction of your current account on every trade. The position sizing formula is:

Units = (Account size × Risk %) ÷ |Entry price − Stop price|

For a long trade, the stop is below entry; for a short trade, it is above, so the distance is stop minus entry. Always round the result down so you never exceed your risk.

Example (stock): Suppose your account is $25,000 and you risk 1% per trade.

  1. Dollar risk: $25,000 × 0.01 = $250.
  2. You plan to buy at $80 with a stop at $76, below a support level. Stop distance = $80 − $76 = $4.
  3. Shares = $250 ÷ $4 = 62.5, rounded down to 62 shares.
  4. Position value = 62 × $80 = $4,960, about 19.8% of the account.
  5. Actual risk = 62 × $4 = $248, just under the $250 limit.

Now suppose a different setup on the same stock lets you use a $1 stop ($80 entry, $79 stop). Shares = $250 ÷ $1 = 250, a $20,000 position, 80% of your account. Risk is still $250, but you are now heavily concentrated in one stock, and an overnight gap through your stop would hurt far more.

That second case shows why many traders add a second limit: a maximum position size, such as 20% or 25% of the account per position. Calculate size from the stop, then cap it at your maximum. Use whichever number is smaller.

Position sizing and stop loss placement

The stop should come from the chart, not from the size you want. Place it where the trade idea is invalid, such as below support, below a recent swing low or beyond a moving average, then calculate size. Moving a stop closer just to buy more shares puts it inside normal price noise and gets you stopped out more often. Our guide to stop loss, stop limit and trailing stop orders explains which order type to use, and the risk-reward ratio guide shows how to judge whether the target justifies the stop.

A simple position sizing calculator

You do not need special software. A spreadsheet with four inputs works as a position sizing calculator:

  • Cell B1: account size (for example 25000)
  • Cell B2: risk % as a decimal (0.01)
  • Cell B3: entry price (80)
  • Cell B4: stop price (76)
  • Shares: =ROUNDDOWN(B1*B2/ABS(B3-B4),0)
  • Position value: shares × entry; actual risk: shares × ABS(B3−B4)

For crypto, change the rounding to the decimal places your exchange allows, such as 4 or 5 for bitcoin.

Position Sizing for Crypto

The formula is the same for crypto, but two things change. You can usually buy fractions of a coin, and price swings are much larger, so stops tend to be wider and positions smaller.

Example (crypto): Suppose you have a $10,000 account, risk 1%, and want to buy bitcoin at a hypothetical $60,000 with a stop at $57,000.

  1. Dollar risk: $10,000 × 0.01 = $100.
  2. Stop distance: $60,000 − $57,000 = $3,000 (5%).
  3. Position = $100 ÷ $3,000 = 0.0333 BTC.
  4. Position value: 0.0333 × $60,000 ≈ $2,000, or 20% of the account.

Fees and slippage add to the loss. If you pay 0.1% to enter and 0.1% to exit on a $2,000 position, that is about $4. On a fast move, the fill at your stop could be worse still. Some traders reduce their dollar risk by a small buffer, say to $90, to absorb those costs.

Altcoins with lower trading volume can move 10% to 20% in a day, so a sensible stop may be 15% away. At 1% risk, that means a position of roughly 6.7% of your account ($100 ÷ 0.15 ≈ $667 on $10,000). Small positions in volatile coins are the formula working as intended, not a sign you are being too cautious.

Volatility-Based Position Sizing With ATR

Instead of setting stops by chart levels alone, many traders size positions by volatility. The usual tool is the Average True Range (ATR), an indicator developed by J. Welles Wilder. True range is the largest of three values: today’s high minus today’s low, the gap from yesterday’s close to today’s high, or the gap from yesterday’s close to today’s low. ATR averages that over a period, usually 14 bars.

A common rule places the stop a multiple of ATR from entry, such as 2 × ATR, and then sizes the position from that distance:

Units = (Account × Risk %) ÷ (ATR × multiple)

Example (ATR sizing): Suppose you have $25,000 and risk 1% ($250). You compare two stocks, both priced at $120.

  • Stock A has a 14-day ATR of $3. Stop distance = 2 × $3 = $6. Shares = $250 ÷ $6 = 41.7, rounded down to 41 shares ($4,920 position).
  • Stock B has a 14-day ATR of $6. Stop distance = 2 × $6 = $12. Shares = $250 ÷ $12 = 20.8, rounded down to 20 shares ($2,400 position).

The more volatile stock gets about half the position, so a typical bad day costs you roughly the same amount in each trade.

ATR sizing keeps your stops outside normal daily noise and makes risk comparable across a calm utility stock, a fast-moving tech stock and a cryptocurrency. Its weakness is that volatility changes. After a quiet stretch, ATR shrinks and positions grow, just before volatility may return.

The Kelly Criterion and Why Traders Use a Fraction of It

The Kelly criterion, published by Bell Labs researcher John L. Kelly Jr. in 1956, calculates the fraction of capital to bet that maximizes long-term growth, given your odds. For a trade where you either win R times your risk or lose your risk, the formula is:

Kelly % = W − (1 − W) ÷ R

where W is your win rate and R is your average win divided by your average loss. The result is the fraction of your account to risk on each trade.

Example (Kelly): Suppose your journal shows a 55% win rate (W = 0.55) and your average win is 1.5 times your average loss (R = 1.5).

  • Kelly % = 0.55 − (0.45 ÷ 1.5) = 0.55 − 0.30 = 0.25, or 25% of the account at risk per trade.
  • Half Kelly = 12.5%. Quarter Kelly = 6.25%.

Now see how sensitive that number is. If your true win rate is 50%, Kelly falls to 0.50 − 0.50 ÷ 1.5 ≈ 16.7%. At 45%, it is about 8.3%. At 40%, it is 0%: there is no edge and you should not trade the strategy at all.

That sensitivity is why almost nobody trades full Kelly:

  • Your inputs are estimates. A win rate measured over 50 or 100 trades can easily be off by five or ten percentage points, and markets change. Overestimate your edge and Kelly tells you to over-bet.
  • Over-betting is punished harder than under-betting. In the example above, betting twice the Kelly fraction (50%) gives a negative expected growth rate even though the strategy has an edge.
  • Full Kelly is a rough ride. Drawdowns of 50% or more are normal at full Kelly, which few people can tolerate.
  • Fractions keep most of the benefit. In theory, half Kelly earns about 75% of the full-Kelly growth rate with far smaller swings. In the example above, half Kelly produces about 75% of the growth and quarter Kelly about 44%.

In practice, Kelly is most useful as a ceiling and a sanity check. If your fixed-fractional risk of 1% is far below even quarter Kelly, you are being conservative, which is fine while your edge is unproven. If Kelly comes out at zero or below, the strategy needs work before any position size is right.

Method How size is set Pros Cons
Fixed dollar amount Same dollars invested in every trade Very simple Risk varies wildly with stop distance
Fixed fractional (1% rule) Same % of account risked to the stop Consistent risk; scales with account Needs a defined stop on every trade
ATR / volatility-based Stop and size based on recent volatility Comparable risk across assets Sizes grow when markets are unusually calm
Fractional Kelly Fraction of edge-based optimal bet Ties size to measured edge Very sensitive to estimation errors

Position Size vs Leverage

Leverage is the ratio of your total position value to your account equity. If you hold $20,000 of positions with a $10,000 account, you are using 2:1 leverage. Margin accounts, futures, CFDs and crypto perpetual contracts all let you take positions larger than your cash.

Here is the key point: if you size from your stop, leverage changes how much margin you post, not how much you risk. In the crypto example above, a $2,000 bitcoin position risks $100 at the stop whether you pay for it in full or post $200 of margin at 10x. The loss at the stop is still $100.

Leverage becomes dangerous when it is used to make the position bigger than your sizing allows. With the same $10,000 account at 10x, a trader could open a $100,000 position. A 5% drop then costs $5,000, half the account, in one trade. And on leveraged crypto contracts, the exchange liquidates your position when your margin runs out. At 20x, that can happen after a move of less than 5%, so you may be closed out before your planned stop is reached.

Rule of thumb: calculate position size from your stop first, then use only as much leverage as that size requires. Check that your liquidation price sits well beyond your stop, not in front of it.

Common Position Sizing Mistakes

  • Sizing by conviction. Doubling size because a trade “looks perfect” makes your biggest losses come from your most confident ideas.
  • Using buying power instead of equity. Base risk on your own money, not on the margin your broker would lend you.
  • Rounding up. 62.5 shares becomes 62, not 63. Small overruns add up across many trades.
  • Ignoring gaps, fees and slippage. A stop is not a guaranteed exit price. Earnings, news and weekend crypto moves can fill you well past it.
  • Forgetting correlation. Five positions in related stocks at 1% each can behave like one 5% bet.
  • Never recalculating. Fixed fractional sizing should use your current balance. After a 20% drawdown, 1% of the smaller account is a smaller dollar risk, which slows losses automatically.
  • Tightening stops to buy more. A stop placed inside normal volatility gets hit more often, so the bigger size does not help.

Your trading style also affects sizing. Day traders often risk less per trade because they take more trades, while swing traders hold through overnight gaps. See day trading vs swing trading vs scalping for how the styles differ.

Bottom Line

Position sizing turns a vague sense of “not too much” into a number. Pick a risk per trade, usually 1% or less while you are learning, let the chart set the stop, and divide one by the other. Cap any single position at a sensible share of the account, adjust for volatility with ATR if you trade different kinds of assets, and treat the Kelly criterion as a ceiling rather than a target. Keep leverage at the level your size requires and no more. For related guides, visit our trading hub.

Sources

Frequently asked questions

What is the position sizing formula?

Position size = (account size × risk per trade %) ÷ (entry price − stop price). For a $10,000 account risking 1% with a $2 stop distance, that is $100 ÷ $2 = 50 shares. For short trades, use stop minus entry, and always round down.

How do I use a position sizing calculator?

Enter your account equity, the percentage you want to risk, your entry price and your stop price. The calculator divides the dollar risk by the stop distance to give the number of shares or coins. You can build one in a spreadsheet with =ROUNDDOWN(account*risk/ABS(entry-stop),0).

What is the difference between position size and risk?

Position size is how much money you put into a trade; risk is how much you lose if your stop is hit. A $5,000 position with a stop $1 below a $50 entry risks only $100, while a $1,000 position with no stop can lose $1,000.

How are position sizing and stop loss related?

You set the stop first, based on where the trade idea is wrong, then calculate size from the distance to it. A wider stop means fewer shares and a tighter stop means more, so the dollar loss at the stop stays the same.

How much should I risk per trade as a beginner?

Most educators suggest 0.5% to 1% of your account, with 2% as an upper limit. At 1%, ten straight losses cost about 9.6% of your account, which is recoverable. Keep risk small until your journal shows a positive track record over many trades.

Should I use the Kelly criterion for trading?

Use it as a ceiling, not a target. Full Kelly assumes you know your exact win rate and payoff, which you never do, and over-betting reduces long-term growth. Traders who use it typically risk a quarter to a half of the Kelly fraction, or less.

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