利息 Rate 計算機 - Simple & Compound 利息

An interest rate calculator answers a practical question: if money is set aside or borrowed at a stated annual rate, what interest accrues and what is the future value? The distinction between simple and compound interest is the whole method. Simple interest is charged only on the original principal. Compound interest is charged on principal plus interest already credited, so the balance grows faster as the compounding frequency rises. For simple interest the calculator multiplies principal by the annual rate and by time in years. A $10,000 balance at 5% for three years earns $1,500 and finishes at $11,500. For compound interest it uses future value = principal × (1 + rate ÷ periods per year)^(periods per year × years). The same $10,000 at 5% compounded monthly for three years grows to about $11,614.72. The effective annual rate converts a nominal rate and compounding schedule into a true yearly yield, which is why monthly or daily compounding beats annual compounding at the same advertised rate. Use the interest rate calculator when comparing a savings account, certificate of deposit, personal loan, or vendor quote that states a nominal annual rate. Keep the rate and the time period on the same annual basis as the field labels. Do not mix a monthly rate with a time period entered in years unless you convert first. The compounding control matters only for compound interest; simple interest ignores it except for displaying total periods. The model does not add origination fees, early-withdrawal penalties, tax on interest, or rate changes during the term. Banks may use actual/365 or average daily balance methods that differ by a few dollars from this closed-form estimate. Treat the result as a planning figure. Confirm the product’s compounding convention and any fees with the institution before you lock in a deposit or a loan.