Yearly interest is the total interest earned or paid on an investment or loan over one year, typically expressed as a percentage. There are two main types: simple interest, calculated on the original amount, and compound interest, which includes interest on both the principal and previously earned interest. Remember, yearly interest influences various financial products, from savings accounts to mortgages. For borrowers, it decides loan repayment costs. On the other hand, for investors, it reveals potential returns and assists in comparing different investment options.