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 type
Position 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.
The share of your portfolio you accept to lose if the stop is hit, e.g. 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
That costs $10,000, which is 20.0% of your portfolio. If the price falls to $95.00 and you sell, you lose $500, which is 1% of your portfolio. On this calculator's own scale, 1% on one trade is in the middle (1% to 2%).
The numbers behind that
Your loss limit for this trade
1% of your $50,000: the most you said you would lose if this trade goes wrong.
$500
What you can lose on one share
You buy at $100.00 and sell at $95.00 if it goes wrong.
$5.00
Shares that fit your loss limit
$500 divided by $5.00, rounded down to whole shares.
100
What the shares cost
100 times $100.00. That is 20.0% of your portfolio in this one company.
$10,000
Loss if your stop is hit
100 times $5.00. That is 1% of your portfolio.
$500
1%
2%
4%
Ten losing trades in a row at this size would take about $4,781 off your $50,000 (9.6%).
The 1% and 2% lines are this calculator's own guidance. They are not a law and not advice.
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 | What the shares cost | Loss if stop is hit |
|---|---|---|---|
| 0.5% | 50 | $5,000 | $250 (0.5%) |
| 1% (yours) | 100 | $10,000 | $500 (1%) |
| 2% | 200 | $20,000 | $1,000 (2%) |
| 3% | 300 | $30,000 | $1,500 (3%) |
Whole shares only, and never with borrowed money. The loss figures assume you sell exactly at your stop price: if the price jumps past it, or you pay fees, the real loss is bigger.
Sizing tells you how much to buy, not whether to buy. Check the idea first with our Margin of Safety calculator.
This calculator sizes a trade from the loss you accept. Give it your portfolio, the percentage you will risk per trade, an entry price and a stop loss, and it returns the largest whole number of shares whose loss at your stop stays within that limit, and that your portfolio can pay for without borrowing.
Max shares = (Portfolio × Risk %) ÷ (Entry − Stop loss)
Step 1: Enter your total trading portfolio.
Step 2: Set your risk per trade: the share of your portfolio you accept to lose if the stop is hit. The example uses 1%.
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?
This calculator's example starts at 1%: a loss of 1% of your portfolio on a single trade. The arithmetic shows why a small figure matters. Ten losses in a row at 1% still leave you with about 90% of your money. The same streak at 5% leaves you with about 60%, and a 40% hole needs a 67% gain just to get back to where you started.
There is no official figure for the right risk per trade. The 1% and 2% lines on this page are this calculator's own guidance, not a law and not advice. Whatever you pick, keep it consistent. Changing your risk per trade based on how sure you feel is how disciplined sizing turns into 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 loss on the trade, if you sell at your stop, stays within a fixed slice of your portfolio. The formula is: max shares = (portfolio × risk%) ÷ (entry price − stop loss).
There is no official figure. This calculator's own scale calls a loss under 1% of your portfolio on one trade cautious, 1% to 2% in the middle, and above 2% aggressive. The arithmetic shows why the size matters: ten losing trades in a row at 1% each take about 9.6% off your portfolio, at 2% about 18.3%, and at 5% about 40.1%. These lines are this calculator's own guidance, not a law and not advice.
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: in place of the share price you buy at and the share price of your stop, use the exchange rate you buy at and the exchange rate of your stop, 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. This calculator itself works in whole shares only.
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
Record Every Position in One Place
Sizing one trade is the start. With a free Worthmap account, you can record every position, each in its own currency, see your net worth in one base currency over time, and use the stock screener and AI analysis. The free plan is in beta.
Create free accountBuilt & maintained by Worthmap · Last updated October 4, 2026
Educational use only. This tool provides estimates for informational purposes and does not constitute financial, investment, tax, or legal advice. Results are based on inputs you provide and mathematical models, they do not guarantee future performance. Always consult a qualified financial adviser before making investment decisions.