I Bond Calculator
Project your Series I Savings Bond earnings. Enter the current composite rate from TreasuryDirect.gov to calculate projected returns.
Last updated: · Enter current rate from TreasuryDirect.gov
A $10,000.00 I Bond at 4.00% composite rate held for 5.0 years would be worth approximately $12,189.94, earning $2,189.94 in interest.
Results
Important Note About This Projection
This projection assumes the current composite rate of 4.00% stays constant. In reality, the inflation component resets every 6 months based on CPI changes. The fixed rate componentnever changes for your bond, but the inflation rate will fluctuate. Actual returns may be higher or lower than shown.
How This Is Calculated
I Bond interest compounds semi-annually. The composite rate is applied to the bond's value every 6 months.
Composite Rate = Fixed Rate + (2 × Inflation Rate) + (Fixed Rate × Inflation Rate)The value after n semi-annual periods:
Value = Principal × (1 + Composite Rate / 2)nData source
I Bond rates are fetched live from the Treasury Fiscal Data API (no authentication required). Also published at TreasuryDirect.gov. Rates change semi-annually (May 1 and November 1).
Important caveat
This projection assumes the current composite rate remains constant. In reality, the inflation component resets every 6 months. The fixed rate never changes for your specific bond, but the inflation rate will vary with CPI.
Frequently Asked Questions
- How do I Bond interest rates work?
- I Bonds earn a composite rate made up of two parts: (1) a fixed rate, set when you buy the bond and locked for its 30-year life, and (2) an inflation rate, which adjusts every 6 months based on changes in the Consumer Price Index (CPI-U). The composite rate formula is: [Fixed rate + (2 × inflation rate) + (fixed rate × inflation rate)]. Rates are announced by the Treasury on May 1 and November 1 each year.
- What is the early redemption penalty for I Bonds?
- I Bonds must be held for at least 12 months. If you redeem before 5 years, you lose the last 3 months of interest as a penalty. After 5 years, there is no penalty.
- What is the I Bond purchase limit?
- You can buy up to $10,000 per person per calendar year in electronic I Bonds through TreasuryDirect.gov. You can also buy up to $5,000 in paper I Bonds using your federal tax refund (Form 8888), for a total of $15,000 per year.
- Are I Bonds taxable?
- I Bond interest is exempt from state and local income tax. Federal tax can be deferred until you redeem the bond or it matures (up to 30 years). If used for qualified higher education expenses, the interest may be completely tax-free at the federal level as well (income limits apply).