If I am figuring this correctly, unless the fixed rate of an I Bond is at least 3% (the percent that is added to the inflation rate), then one's investment loses purchasing power, after taxes are factored in.
Consider:
$1000 I Bond
Inflation: 5%
I Bond Fixed Rate 1.2%
Value after one year: $1062 (1000 X 6.2%)
Value after one year after taxes subtracted (33% tax bracket) =
$1062 - $20.6 = $1041
Thus your investment is worth $1041 after taxes, but to keep even with inflation, your investment would have to be $1050.
Consider:
$1000 I Bond
Inflation: 5%
I Bond Fixed Rate 1.2%
Value after one year: $1062 (1000 X 6.2%)
Value after one year after taxes subtracted (33% tax bracket) =
$1062 - $20.6 = $1041
Thus your investment is worth $1041 after taxes, but to keep even with inflation, your investment would have to be $1050.