Frequently Asked Questions

The compound interest calculator uses the standard formula: A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate as a decimal, n is the number of compounding periods per year (e.g., 12 for monthly), and t is the time in years. For continuous compounding, the formula is A = Pe^(rt). Our calculator supports daily, monthly, quarterly, and annual compounding.

Each monthly payment is split between interest and principal using the amortization formula: Monthly Payment = P × [r(1+r)^n] ÷ [(1+r)^n − 1], where P is the loan balance, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of payments. For each period, the interest portion = remaining balance × monthly rate, and the principal portion = monthly payment − interest. The balance decreases with each payment.

The daily periodic rate (DPR) is your Annual Percentage Rate (APR) divided by 365. For example, an 18% APR has a DPR of 18% ÷ 365 = 0.04932% per day. Credit card interest is typically calculated as: Average Daily Balance × DPR × Number of Days in Billing Cycle. Our Credit Card Payoff Calculator accounts for the DPR when projecting your payoff timeline and total interest paid.

Break-even analysis finds the point where total revenue equals total costs. The formula is: Break-Even Units = Fixed Costs ÷ (Selling Price − Variable Cost Per Unit). For example, with $10,000 fixed costs, a $50 selling price, and $30 variable cost, break-even is $10,000 ÷ ($50 − $30) = 500 units. Our calculator also shows a sensitivity table with break-even at ±20% price and cost variations.

ROI = ((Net Profit ÷ Cost of Investment) × 100). Net Profit = Final Value − Initial Investment. For example, investing $10,000 that grows to $13,500 gives ROI = ((13,500 − 10,000) ÷ 10,000) × 100 = 35%. Our ROI Calculator also computes Annualized ROI using the CAGR formula: Annualized ROI = (Final Value / Initial Investment)^(1/years) − 1.

The standard conversion assumes a 40-hour work week and 52 weeks per year (2,080 working hours). Hourly rate = Annual Salary ÷ 2,080. For example, a $62,400 annual salary equals $30/hour. Our Salary Converter also accounts for vacation weeks and shows monthly, biweekly, weekly, and daily equivalents. You can adjust the hours per week for non-standard schedules.

Simple interest is calculated only on the principal: Interest = P × r × t. Compound interest is calculated on the principal plus previously accumulated interest, so interest grows exponentially over time. For example, $10,000 at 5% for 10 years: simple interest = $5,000 (total $15,000); compound interest monthly = $6,470 (total $16,470). The difference grows significantly over longer periods.

Yes. All 7 calculators — Compound Interest, Loan Amortization, Savings Goal, ROI Calculator, Salary Converter, Credit Card Payoff, and Break-Even Calculator — are completely free with no account required. For major financial decisions such as mortgages or investments, always consult a licensed financial professional.