Many pundits recommend buying life insurance equal to a multiple of your salary. For example, one financial advice columnist recommends buying insurance equal to 20 times your salary before taxes. She chose 20 because, if the benefit is invested in bonds that pay 5 percent interest, it would produce an amount equal to your salary at death, so the survivors could live off the interest and wouldn’t have to “invade” the principal.
However, this simplistic formula implicitly assumes no inflation and assumes that one could assemble a bond portfolio that, after expenses, would provide a 5 percent interest stream every year. But assuming inflation is 3 percent per year, the purchasing power of a gross income of $50,000 would drop to about $38,300 in the 10th year. To avoid this income drop-off, the survivors would have to “invade” the principal each year. And if they did, they would run out of money in the 16th year.
The “multiple of salary” approach also ignores other sources of income, such as those mentioned previously.