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I Bond Calculator

Estimate your I Bond's current value and future return based on the current composite rate.

Updated July 2026 · Figures verified July 2026 (sources) · Editorial standards

Composite rate
4.26%
Value after 5 yrs
$12,343
Total interest
$2,343
Value after 1 year$10,430After-tax value$11,828Effective ann. yield4.30%

I Bond Details

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yrs
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Key figures

Composite rate
4.26%
Value after 5 yrs
$12,343
Total interest
$2,343
After-tax value
$11,828
Effective ann. yield
4.30%

$10,000 in I Bonds (composite rate 4.26%) grows to $12,343 after 5 years — $2,343 in interest, $11,828 after 22% federal tax.I Bond interest is exempt from state and local taxes, and federal tax is deferred until redemption. The composite rate = fixed + 2×semiannual-inflation + (fixed × semiannual-inflation), and adjusts every 6 months.

Composite rate
4.26%
By KalkWiseVerified against official sources Updated July 2026

What is the i bond calculator — savings bond value & rate?

In short

I Bonds issued May–October 2026 pay a 4.26% composite rate: 0.90% fixed + 2 × 1.67% semiannual inflation (TreasuryDirect, May 1, 2026). The inflation part resets every May and November, so long-term results are not guaranteed — if 4.26% held constant, $10,000 would grow to about $12,343 in 5 years with no penalty (redeeming before 5 years forfeits the last 3 months of interest).

Calculates your I Bond composite rate from fixed + inflation components, projects final value with the 3-month penalty for early redemption (before 5 years), and shows after-tax value.

How to use this calculator

  1. 1Enter purchase amount (max $10,000/yr per person).
  2. 2Enter current fixed rate and annualized inflation rate from TreasuryDirect.gov.
  3. 3Enter your hold period (1–30 years) and federal tax rate.
  4. 4Calculator applies the 3-month penalty automatically if you hold fewer than 5 years.

The formula

composite=fixed+2×inflation+(fixed×inflation)
Composite = fixed + 2×semiInflation + (fixed × semiInflation); Value = Principal × (1 + composite/2)^(years×2)
f
— Fixed rate
i
— Semi-annual inflation rate (annualized ÷ 2)
composite
— Composite = f + 2i + f×i

Worked example

The scenario

$10,000, 0.90% fixed, 3.34% annualized inflation (the May–October 2026 official rates), 5 years, 22% tax — assuming the rate holds constant.

gives

The result

Composite ≈ 4.26%. Value at 5 yrs ≈ $12,343. After-tax ≈ $11,828. Effective yield ≈ 4.30%.

Common use cases

  • Protect savings from inflation with a government-guaranteed bond.
  • Save for education (interest may be federal-tax-free if used for qualified expenses).
  • Compare to HYSA or CD when inflation is elevated.
  • Defer federal tax on interest until redemption.

Limitations & assumptions

  • Maximum $10,000/yr per SSN electronically; $5,000 more via tax refund in paper bonds.
  • Cannot redeem within 12 months of purchase.
  • Early redemption before 5 years forfeits 3 months of interest.
  • Rate resets every 6 months — future composite rates are unknown.

Frequently asked questions

Composite = fixed + 2×semiannual_inflation + (fixed × semiannual_inflation). The fixed rate stays constant for the life of the bond. The inflation adjustment uses the CPI-U change and resets every May 1 and November 1.

Disclaimer: KalkWise calculators are provided for general informational and educational purposes only and do not constitute financial, investment, tax, or legal advice. Results are estimates based on the figures you enter and the assumptions described above. Actual outcomes will vary. Consult a qualified professional before making financial decisions.