Series EE and Series I Savings Bonds are issued by the U.S. Treasury. These bonds have tax advantages—you do not pay state or local income tax on the interest earned, and federal income tax can be deferred until you redeem the bonds or they reach maturity. 

Series EE U.S. Savings Bonds
EE U.S. Savings Bonds interest rates are fixed for 20 years at the time it is issued. The government may adjust the rate after the 20th year. Rates paid on series EE bonds are set twice a year, in May and November, and remain the same for all bonds issued during the following six-month period.

EE bonds come with a guarantee from the U.S. government to at least double in value over the term of the bond, which is commonly 20 years. At maturity, the owner of the bond can redeem the principal or opt to let it collect additional interest for another 10 years beyond the maturity date.

Interest income from EE bonds is exempt from state and local taxes but not from federal taxes. The owner may receive tax relief if the funds go to funding qualified higher education.

Series I U.S. Savings Bonds
Series I savings bonds are a relative newcomer, having been introduced in 1998. Unlike EE bonds, Series I bonds don't come with a guarantee to double in value over 20 years. Instead, Series I bonds are issued for a period of 30 years and have a rate of return that is fixed for the life of the bond plus an inflation-adjusted interest rate.

The adjustable-rate is revised semi-annually, in May and November, and is based on the Consumer Price Index for All Urban Consumers (CPI-U).

Differences
One potential bonus is that Series I bonds if used to pay the costs of higher education, may be exempt from federal taxes as well as state and local taxes—the bond must be redeemed and the proceeds used in the same calendar year to qualify.

The key difference between the two types of savings bonds is that adjustable rate. Series I bonds do not carry the same guarantee of doubling in value over 20 years, but they do have a built-in inflation adjustment.

What's the worst that could happen? The owner of a Series I bond could be hit with years of low inflation or even deflation, and fail to get the doubling in value over time.

Education Savings Bond Program
The Education Savings Bond Program permits qualified taxpayers to exclude from their gross income all or a portion of the interest earned on the redemption of eligible Series EE and Series I Bonds issued after 1989. You must be at least 24 years old before the bond's issue date. To qualify for this exclusion, the taxpayer, the taxpayer's spouse, or the taxpayer's dependent at certain post-secondary educational institutions must incur tuition and other educational expenses

For redemptions in 2020:

• The interest is completely tax-free for joint filers with modified AGI less than $119,300 and $79,550 for all other taxpayers (sames as in 2019).
• The interest is only partially taxable for joint filers whose modified AGI is over the above threshold and less than $151,600 and $96,100 for all other taxpayers (same as in 2019).
• The interest is completely taxable for joint filers whose modified AGI is $151,600 and above $96,100 for all other taxpayers (sames as in 2019).

This exclusion is not available to married individuals who file separate returns.

In order to get this federal tax break, the bonds generally must be purchased by a parent, the parent must be at least 24 years old, and the bonds can never be in the child's name. Form 8815 (Exclusion of Interest from Series EE and I U.S. Savings Bonds Issued after 1989) is used to figure out how much of the interest can be excluded from income.