Money & Finance Calculators
Tip calculator, sales tax, discount/markup, hourly↔salary, loan payments, rent affordability, cost comparison.
📘 When to use these
Splitting a dinner bill, budgeting rent, comparing grocery prices, or understanding loan payments. Money math you use every day.
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Option A
Option B
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📚 Understanding Money Math
💡 The 50/30/20 Budget Rule
50% of income → needs (rent, food, utilities). 30% → wants (entertainment, dining out). 20% → savings and debt payoff. This simple framework works for most people and prevents overspending.
💡 The Real Cost of Debt
A $10,000 credit card balance at 20% APR with minimum payments takes 31 years to pay off and costs $24,753 total. Always check the total cost of a loan, not just the monthly payment.
💡 Rent: The 30% Rule
Financial experts recommend spending no more than 30% of gross income on rent. Earning $60K/year? Max rent = $1,500/month. Going above 30% squeezes savings and creates financial stress.
💡 Unit Price: The Hidden Savings
Always compare unit prices (price per oz, per count) rather than total price. The bigger package isn't always cheaper per unit. Most grocery stores show unit prices on shelf labels — look for them!
🧮 Common Formulas Used Above
Tip = Bill × (Tip% ÷ 100)
Sales Tax = Price × (Tax Rate ÷ 100)
Discount Price = Original × (1 - Discount% ÷ 100)
Annual Salary = Hourly × Hours/Week × 52
Monthly Payment = P × [r(1+r)ⁿ] ÷ [(1+r)ⁿ - 1] (amortization formula)
Cost Per Unit = Total Price ÷ Quantity