Future values depend critically on the assumed interest rate, particularly for long$-$lived investments. Figure $4\mathrm{.}2$ illustrates this relationship by plotting the growth of $1$ for different rates and lengths of time. Notice that the future value of $1$ after $10$ years is about $6\mathrm{.}20$ at a $20$ per cent rate, but it is only about $2\mathrm{.}60$ at $10$ per cent. In this case, doubling the interest rate more than doubles the future value.