A savings bank is selling long-term savings certificates that pay interest at the rate of 7\frac{1}{2}% per year, compounded continuously. The bank claims that the actual annual yield of these certificates is 7.79%. What does this mean?
The nominal interest rate is 7\frac{1}{2}%. Since the interest is compounded continuously, the effective annual interest rate is given by (5.1) as
i = \underset{m→∞}{\lim}\left[\left(1 + \frac{r}{m}\right)^m – 1\right] = e^r – 1 (5.1)
i = e^{0.075} – 1 = 0.077884 ≈ 7.79%
Formula (5.1) is very convenient, provided a calculator is available to carry out the exponentiation. Tabulated values of the effective annual interest rate may be used instead; see Appendix B.