Step 1:
Effective annual rate measures the actual annual return when compounding occurs multiple times in a year.
Step 2:
If nominal annual rate is $r$ compounded $m$ times yearly, then:
\[
r_e=\left(1+\frac{r}{m}\right)^m-1
\]
Step 3:
• $\frac{r}{m}$ gives periodic rate
• Raising to power $m$ accounts for compounding
• Subtracting 1 converts amount factor into effective rate
Step 4:
Therefore, the effective rate formula is:
\[
\boxed{\left(1+\frac{r}{m}\right)^m-1}
\]
Hence, the correct answer is:
\[
\boxed{\text{(4)}}
\]