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Financial Calculations Guide

Always use minor units (cents/paisa) for money calculations.

Money Type​

interface Money {
  amount: number; // In minor units
  currency: string;
}

Constants​

Use constants from shared/financial-constants.ts:

import { DAYS_PER_YEAR, BASIS_POINTS_SCALE } from "@shared/financial-constants";

Utilities​

Use utilities from shared/financial-calculations.ts:

import { applyBpsToMinor } from "@shared/financial-calculations";

const fee = applyBpsToMinor(1000000, 250); // 2.5% of amount

Why Minor Units?​

Avoids floating-point precision errors:

// ❌ BAD
const total = 10.1 + 0.2; // 10.299999999999999

// ✅ GOOD
const total = 1010 + 20; // 1030