About Simple Interest Calculator

Computes simple interest using the formula I = (P × R × T) / 100 for both investment and loan scenarios. Accepts principal, annual rate, and time period in years, months, or days. For loans, also calculates the equal monthly payment by dividing total amount by total months. Results update live, with preset scenarios (personal loan, savings account, short-term investment, car loan) for quick demonstration. Exportable as JSON.

• Time unit conversion: months ÷ 12, days ÷ 365 to normalize to years
• Loan mode displays monthly payment: (Principal + Interest) ÷ (years × 12)
• Investment mode uses green accent; loan mode uses blue accent for visual differentiation
• Four preset examples with pre-filled values for common financial scenarios
• Formula reference card shown below results for transparency

Frequently Asked Questions

How does simple interest differ from compound interest?

Simple interest is calculated only on the original principal: $10,000 at 5% for 3 years always earns $1,500. Compound interest recalculates on the growing balance each period, so you earn interest on interest. For short terms and low rates the difference is small; for long terms it is dramatic.

Is the monthly payment calculation accurate for real loans?

It divides total repayment evenly across all months, which is how simple-interest loans work. Most real-world loans use compound interest with amortization schedules, where early payments are interest-heavy. This calculator is accurate for simple-interest instruments like some auto loans and short-term personal loans.