Finance Domain

Finance Domain Knowledge

Core Concepts

Transaction Types

• Income: Salary, freelance, investment returns, gifts
• Expense: Bills, shopping, food, transport, entertainment
• Transfer: Between own accounts (NOT income or expense)

Account Types

• Cash: Physical cash tracking
• Bank: Checking/savings accounts
• Credit Card: Credit accounts (negative = owed)
• Investment: Stocks, bonds, crypto
• Loan: Mortgages, personal loans (negative balance)

Financial Calculations

CRITICAL: Money Handling

// ALWAYS use Decimal for money — NEVER Double
let amount: Decimal = 1_000_000  // ✅
let amount: Double = 1_000_000   // ❌ floating point errors

// Rounding for display
let rounded = NSDecimalNumber(decimal: amount)
    .rounding(accordingToBehavior: NSDecimalNumberHandler(
        roundingMode: .bankers,
        scale: 0,  // VND has 0 decimal places
        raiseOnExactness: false,
        raiseOnOverflow: false,
        raiseOnUnderflow: false,
        raiseOnDivideByZero: true
    ))

Budget Tracking

Budget Remaining = Budget Amount - Sum(Expenses in Period)
Budget Usage % = Sum(Expenses) / Budget Amount * 100
Daily Average Spending = Sum(Expenses in Month) / Days Elapsed
Projected Month Spend = Daily Average * Days in Month

Net Worth Calculation

Net Worth = Sum(Asset Accounts) - Sum(Liability Accounts)
Assets = Cash + Bank + Investment (positive balances)
Liabilities = Credit Card debt + Loans (negative balances)

Vietnamese Currency (VND)

• ISO code: VND
• Symbol: ₫
• Decimal places: 0 (no cents)
• Number format: 1.000.000 ₫ (dot as thousands separator)
• Use Locale(identifier: "vi_VN") for formatting