I Bond Calculator 2026 – Value, Interest and Early-Cash-In Penalty

This I bond calculator projects the value of a US Series I savings bond. It uses the current composite rate for the first six months, then your inflation estimate on top of the fixed rate, and shows interest, the early-cash-in penalty and the after-tax value.

Amount invested ($, up to $10,000 a year)

Fixed rate (%) – 0.90% for May–Oct 2026

Current composite rate (%) – 4.26% for May–Oct 2026

Inflation you expect after the first 6 months (% a year)

Years you will hold it

Federal tax rate on the interest (%)

Current I bond rate

Bought	Fixed rate	Semiannual inflation rate	Composite rate
May 1 – October 31, 2026	0.90%	1.67%	4.26%

The Treasury sets new rates every 1 May and 1 November. The fixed rate stays with the bond for its whole 30-year life; the inflation part changes every six months.

How the composite rate is calculated

Composite = fixed + 2 × semiannual inflation + fixed × semiannual inflation

For May 2026: 0.0090 + 2 × 0.0167 + 0.0090 × 0.0167 ≈ 4.26%.

Key rules

Buy up to $10,000 per person per calendar year online through TreasuryDirect.
You cannot cash in for the first 12 months.
Cash in before 5 years and you lose the last 3 months of interest.
Interest is exempt from state and local tax, and federal tax can be deferred until you cash in.

Worked example

$10,000 bought at 4.26%, then earning about 3.4% with 2.5% inflation, is worth about $11,892 after 5 years, with no penalty.

Frequently asked questions

What is the I bond rate right now?

4.26% for bonds bought from May 1 to October 31, 2026, made up of a 0.90% fixed rate and inflation. A new rate is announced on November 1.

Can I bond rates go below zero?

No. The composite rate has a floor of zero, so your bond’s value can never fall.

How much can I invest in I bonds?

$10,000 per person per calendar year in electronic bonds. Paper I bonds bought with tax refunds are no longer offered.

Are I bonds better than a CD or high-yield savings account?

It depends on rates and how long you can lock money away. I bonds protect against inflation, but you cannot cash them in for a year and lose 3 months of interest before 5 years.

Related calculators

Sources

Last reviewed: October 2026. For information only; not financial, tax or legal advice. Results are estimates.