Stock Position Size Calculator
How many shares to buy so one bad trade cannot hurt you
Enter your trade and see how many shares to buy
Free · No sign-up · Updates as you typePosition sizing decides whether one losing trade costs you 1% of your money or 20%. You pick how much you are willing to lose if you are wrong; the tool works backward to the number of shares that keeps the loss to exactly that.
$
All the money you trade with, e.g. 50,000.
How much of your portfolio you will lose if the stop hits. Most use 1%.
$
The price you plan to buy at, e.g. 100.
$
Where you sell if you are wrong. Must be below the entry, e.g. 95.
Buy at most
100 shares
= $10,000 position (20.0% of your portfolio)
Standard · 1.0% risk
In plain terms: you set a 1% risk budget on your $50,000. Each share can lose $5.00 (entry $100.00 minus stop $95.00), so 100 shares put $500 at risk if the stop is hit. That buys a $10,000 position, 20.0% of your portfolio.
Most you can lose
$500
Risk per share
$5.00
Position value
$10,000
Share of portfolio
20.0%
How the size changes with the risk you take
Same trade, different risk per trade. Notice how fast the position grows as you risk more.
| Risk per trade | Shares | Position | Style |
|---|---|---|---|
| 0.5% | 50 | $5,000 | Conservative |
| 1% (yours) | 100 | $10,000 | Standard |
| 2% | 200 | $20,000 | Standard |
| 3% | 300 | $30,000 | Aggressive |
What this means: 1 to 2% per trade is the standard professional rule. It funds a meaningful position while keeping a string of losses survivable.
Sizing tells you how much to buy, not whether to buy. Check the idea first with our Margin of Safety calculator.
This calculator uses the standard risk-based position sizing rule the pros use. Give it your portfolio, the percentage you will risk per trade, an entry price, and a stop loss, and it returns the exact number of shares to buy so the loss at your stop equals, and never exceeds, your target risk.
Max shares = (Portfolio × Risk %) ÷ (Entry − Stop loss)
Step 1: Enter your total trading portfolio.
Step 2: Set your risk per trade. 1% is the default. Beginners should not go higher; pros rarely pass 2%.
Step 3: Enter the price you plan to buy at and the stop-loss where you would exit if wrong.
Step 4: Read the number of shares and the share of your portfolio it represents, updated as you type.
What Is Position Sizing?
Position sizing is the most underrated edge in trading. Entry timing, stock picking, and stop placement get all the attention, but the single choice that decides how long you last is how much you put on each trade. A trader who wins 60% of the time can still go broke with poor sizing; a trader who wins 40% of the time can compound steadily with disciplined sizing.
A position size calculator answers one question: given a portfolio, a risk you will accept per trade, an entry, and a stop, how many shares should you buy? The arithmetic is easy. The discipline of actually running it before every trade, rather than sizing by gut, is what separates real risk management from guessing.
The Formula, Explained
Max shares = (Portfolio × Risk %) ÷ (Entry − Stop loss)
The top of the fraction (portfolio × risk %) is the most money you are willing to lose on the trade. The bottom (entry − stop) is what you lose per share if the stop hits. Divide them and you get the most shares that, at the stop, deliver exactly your target loss. With a $50,000 portfolio, 1% risk, a $100 entry and a $95 stop: max loss is $500, risk per share is $5, so you buy 100 shares, a $10,000 position, 20% of the portfolio.
Notice the position in dollars (20% of the portfolio) is far bigger than the risk (1%). That is the leverage of a tight stop: most of the trade survives the stop, so a small risk can fund a meaningful position. It also explains why a wider stop forces a smaller position, the maths makes you size down when the idea carries more uncertainty.
How Much Should You Risk per Trade?
The most common rule is the 1% rule: never risk more than 1% of your capital on a single trade. The maths is unforgiving. Ten losses in a row at 1% still leave you with about 90% of your money. The same streak at 5% leaves you with 60%, and the despair of a 40% drawdown is what ends most trading careers.
Long-term investors often risk just 0.25 to 0.5% per stock inside a diversified portfolio. Aggressive short-term traders sometimes reach 2%, but rarely more. Whatever you pick, keep it consistent. Changing your risk per trade based on how sure you feel is exactly how disciplined sizing turns into reckless betting.
Position Sizing for Forex and Other Markets
The same idea works in forex: swap shares for lots, and risk per share for risk per pip times the pip distance. On a $25,000 account, 1% risk is $250. If your stop is 50 pips away and a standard lot is $10 per pip, your size is half a standard lot ($250 ÷ (50 × $10)). The framework extends to options (size by the premium at risk), futures (tick value × stop distance), and crypto (a volatility-based stop). In every market the backbone is the same: decide the most you can lose, then size so the stop honours it.
Frequently Asked Questions About Position Sizing
Position sizing is deciding how many shares to buy so that your worst-case loss on the trade stays within a fixed slice of your portfolio. The common rule is to risk no more than 1 to 2% of capital on any one trade. The formula is: max shares = (portfolio × risk%) ÷ (entry price − stop loss).
Most professionals use 1% per trade. Beginners are wise to start at 0.5 to 1% while they learn. Above 2% is aggressive: a run of five or six losses can wipe 10 to 15% off your capital before a single winner. Long-term investors often risk just 0.25 to 0.5% per stock inside a diversified portfolio.
A wider stop (further from your entry) means each share can lose more, so you can buy fewer shares for the same risk. A tighter stop lets you hold more shares for the same dollar risk, but it is easier to get knocked out by normal price noise. Set the stop from the chart and the volatility, not from how many shares you wish you could own.
Yes. The same formula applies: swap entry and stop prices for the entry and stop rates, and "shares" becomes units or lots. For pip-based stops, divide your max risk in money by (pip distance × pip value per lot) to get the size in lots. The 1 to 2% rule is the same across asset classes.
For small trades, yes. Take your round-trip costs off the max risk before you size. If you risk $100 and expect $4 in commission plus $2 of slippage, size the trade on $94, not $100. With commission-free brokers and liquid large-caps, this rarely moves the answer much.
For a deeper dive, read our companion article: Position Sizing for Stocks: How Much to Buy and Why
Track Position Sizes Across Your Whole Portfolio
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