How to use the I bond calculator
- 1 Enter the amount you invest (up to $10,000 a year online).
- 2 Check the fixed rate and six-month inflation rate; they default to the current rates.
- 3 Enter how many years you plan to hold.
- 4 Read the value, interest and any early cash-in penalty.
Worked example
$10,000 in I bonds bought in November 2026, held for 5 years at a steady 5.51%. Interest compounds every six months, so the bond grows to about $13,122, earning $3,122. Cashing in after one year would give about $10,416, after losing three months of interest.
Buying I bonds wisely
- Buy before April 30, 2027 to lock in the 1.40% fixed rate.
- Hold at least five years to avoid the 3-month interest penalty.
- Use TreasuryDirect: up to $10,000 a person each year.
- Spread purchases across family members for more.
Compare with price rises in the Inflation Calculator, bank rates in the CD Calculator, and your safety net in the Emergency Fund Calculator.
Features
Treasury formula
Composite = fixed + 2 × inflation + fixed × inflation.
Six-month compounding
Interest added every six months, as TreasuryDirect does.
Penalty shown
Three months of interest lost if cashed before five years.
When to use it
Saving for a goal
Compare with a CD in the CD Calculator.
Emergency fund
I bonds can be cashed after 12 months. Size your fund with the Emergency Fund Calculator.
Beating inflation
Compare with price rises in the Inflation Calculator.
Long-term saving
The 1.40% fixed rate is the highest since 2006. Compare growth with the Compound Interest Calculator.
Related Savings and Investing tasks
Frequently asked questions
What is the I bond rate for November 2026?
5.51% for bonds bought from November 1, 2026 to April 30, 2027. It combines a 1.40% fixed rate with a 2.04% six-month inflation rate.
How is the composite rate worked out?
Fixed rate + (2 × six-month inflation rate) + (fixed rate × six-month inflation rate): 1.40% + 4.08% + 0.03% = 5.51%.
Does the rate change?
The fixed rate never changes. The inflation part resets every six months from your purchase month, based on CPI-U, so your composite rate changes too.
How much can I buy?
$10,000 a year per person in electronic bonds through TreasuryDirect. Paper I bonds through tax refunds are no longer available.
When can I cash in?
After 12 months. If you cash in before 5 years, you lose the last 3 months of interest.
Are I bonds taxed?
Interest is subject to federal income tax but not state or local tax. You can defer it until you cash in, and it may be tax-free if used for qualified education costs.
Can an I bond lose value?
No. The composite rate cannot fall below zero, so the value never goes down.
How long do I bonds earn interest?
For 30 years.
Should I buy now or wait?
The 1.40% fixed rate is locked in for life, so bonds bought by April 2027 keep it. The inflation part changes every six months whenever you buy.
How do I buy I bonds?
Open an account at TreasuryDirect.gov and buy electronic I bonds in any amount from $25, to the penny, up to $10,000 per person per calendar year. Trusts and businesses can buy their own $10,000 too.
Are I bonds better than a CD or savings account?
They protect against inflation and are free of state tax, but you cannot cash them in for the first 12 months and lose three months of interest before five years. A CD or high-yield savings account is more flexible for short-term money.
Results are estimates based on the official rates linked above. Confirm important figures with the issuing authority or a qualified adviser before you act on them.
Built and reviewed by Hamza Farooq, founder and lead developer
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