~/tools/position-size
ToolsPosition size calculator
Risk management runs backwards from the loss: choose what fraction of your account one losing trade is allowed to cost, set where you would exit, and those two numbers decide how big the position can be. This does that arithmetic.
Shares to buy
25
Keeps the loss at your stop to 100.
Position value
1,250
What the position costs to open at your entry price.
Assumes your stop executes at its price. In fast markets fills can be worse than the stop — the loss can exceed the plan.
How this calculator works
The question is not 'how much should I buy?' but 'what am I willing to lose if this goes wrong?'. You set that number as a percentage of your account, then enter your planned entry price and stop-loss. The distance between entry and stop is the risk per share; your allowed loss divided by that distance is the position size. The trade's size becomes a consequence of your risk limit — not of your confidence.
A worked example
A $10,000 account risking 1% may lose $100 on this trade. Entry at $50, stop at $48 — $2 of risk per share. $100 ÷ $2 = 50 shares, a $2,500 position. If the stop is hit, you lose $100: exactly what you decided beforehand, a quarter of the account exposed but one percent risked.
Common questions
- What percentage of my account should I risk per trade?
- Common practice among disciplined traders is 1–2% per trade, and less while learning. The arithmetic is the argument: at 1% risk, ten straight losses — which happen — cost about 10% of the account. At 10% risk, the same streak costs nearly two-thirds. Survival is the strategy.
- Where should the stop-loss go?
- At the price where your reason for the trade is wrong — below a support level, beyond a pattern's failure point — not at a round number chosen to make the position bigger. Set the stop first, from the chart; let this calculator set the size. Doing it in the other order defeats the tool.
- Does a stop-loss guarantee I only lose the planned amount?
- Not always. A gap over a weekend or through news can fill your stop far below its level — slippage the calculator cannot price. Position sizing still caps the damage far better than sizing by feel; it just isn't a hard guarantee in fast markets.
What this tool can't tell you
The tool sizes one trade against one stop. It doesn't know your total exposure across positions, correlation between them, or whether the trade has any edge — sizing controls how much a bad idea costs, not whether the idea is good. The risk-management article carries that half.
These tools are for education. They work from the numbers you type and cannot see your accounts, verify who owns an address, or account for your circumstances. Nothing here is financial advice.