Bond Equivalent Yield. If a Treasury Bill (a discount bond with par value of $10,000) can be bought for $9,950.00, and has 30 days left to maturity, the BEY is calculated by first dividing the par value by the price and subtracting 1 – $10,000/$9,950.00 - 1 – to arrive at a 0.005025, or 0.5025 percent, growth in value over 30 days. Effective Annual Interest Rate: The effective annual interest rate is the interest rate that is actually earned or paid on an investment, loan or other financial product due to the result of The annual interest that is calculated, is calculated for the information only. For example, if you were to buy a T-Bill of $10,000 for $9,900 over a period of 13 weeks then you would have a profit of $100 and a rate of return of 1.01%.