dennisthiessenandClaude Opus 4.8
1951531453
Risk-based sizing on each setup card: shares = floor((account × risk%) / |entry − stop|), with position value and dollars-at-risk. Account size and per-trade risk % are editable inline and persisted in localStorage. Flags when a position would exceed the account (needs margin). Frontend-only. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
38 lines
1.1 KiB
TypeScript
38 lines
1.1 KiB
TypeScript
export interface PositionSize {
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shares: number;
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riskPerShare: number;
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dollarRisk: number;
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positionValue: number;
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/** Position value exceeds the account → needs margin / not affordable in cash. */
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exceedsAccount: boolean;
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}
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/**
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* Risk-based position sizing. Risk a fixed % of the account per trade; the stop
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* distance sets how many shares that budget buys:
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* shares = floor((account × risk%) / |entry − stop|)
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* Returns null when inputs are unusable (no account, no risk, zero stop width).
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*/
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export function positionSize(
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accountSize: number,
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riskPct: number,
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entry: number,
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stop: number,
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): PositionSize | null {
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const riskPerShare = Math.abs(entry - stop);
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if (!(accountSize > 0) || !(riskPct > 0) || !(riskPerShare > 0) || !(entry > 0)) {
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return null;
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}
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const budget = accountSize * (riskPct / 100);
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const shares = Math.floor(budget / riskPerShare);
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const dollarRisk = shares * riskPerShare;
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const positionValue = shares * entry;
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return {
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shares,
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riskPerShare,
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dollarRisk,
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positionValue,
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exceedsAccount: positionValue > accountSize,
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};
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}
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