The problem is that there have been many changes to how savings bonds are purchased and interest is set. With no ability to predict the rate for the entire life of the bond the value at 30 years will be impossible to calculate.
For recent bonds:
What interest will I get if I buy an EE Bond now?
0.20% annual interest rate for EE Bonds issued between May 1, 2013 and October 31, 2013.
EE Bonds issued after May 2005 earn interest for up to 30 years. They
earn a fixed rate of interest. For the first 20 years, EE bonds earn
the same fixed rate that was set when the bond was issued. We may
change the rate or the way an EE Bond earns interest for the last 10
years of the bond's 30-year life. If we make a change, we have to do
it before that 10-year period starts. (This is different from the type
of interest that I Bonds earn. Comparing I Bonds to EE Bonds.)
When will my paper bond be worth its full value?
EE Bonds continue to earn interest for up to 30 years.
Electronic bonds are sold at face value (not half of face value). They
start to earn interest right away on the full face value. Treasury
guarantees that for an electronic EE Bond with a June 2003 or later
issue date, after 20 years, the redemption (cash-in) value will be at
least twice the purchase price of the bond. If the redemption
(cash-in) value is not at least twice the purchase price of the
electronic bond as a result of applying the fixed rate of interest for
those 20 years, Treasury will make a one-time adjustment at the 20
year anniversary of the bond's issue date to make up the difference.
for older bonds
EE Bonds issued May 1997 – April 2005: Interest rate
For the six-month rate periods that start in the months from May 1,
2013 through October 31, 2013, the annual interest rate that applies
to EE Bonds with issue dates from May 1997 through April 2005 is
EE Bonds issued from May 1997 through April 2005 earn a variable rate
of interest. Treasury determines the rate each May 1 and November 1
and applies that rate for six-month rate periods that start in the
next six months.
Again, with no ability to predict the rate for the entire life of the bond the value at 30 years will be impossible to calculate.