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Series I Bond Calculator

US Series I savings bond value. The composite rate is not the fixed rate plus inflation: the official formula includes a cross term, and the fixed rate is locked for the life of the bond.

Also called: series i bond calculator, treasury i bond value.

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Current value
$10,870.66

$10,870.66 after 24 months, from 10,000. The composite rate is 4.22%, combining a fixed 1.2% with the inflation component. Redeeming before five years forfeits the last three months of interest.

Composite rate
4.22%
Interest earned
$870.66
Penalty if redeemed now
$114.63
Net if redeemed now
$10,756.03
On early redemption
Redeeming before five years forfeits the last three months of interest.
On the lock-in
No redemption in the first twelve months, and a three month interest penalty until five years.
How this is calculated
Method and background

This is what the calculation gives for the numbers you entered. It is an estimate, not advice, and it knows nothing about your situation beyond those numbers. Rules for United States change on a published schedule; the effective date is shown on every rule-based tool.

How this is calculated

An I bond combines a fixed rate set at purchase and held for the life of the bond with an inflation rate reset every six months. The composite rate is the fixed rate plus twice the semiannual inflation rate plus the product of the two, which is slightly above simple addition. Bonds cannot be redeemed at all in the first twelve months, and redeeming before five years forfeits the last three months of interest.

the composite rate is not the sum: it includes a cross term between the fixed and inflation components
f
Fixed rate
pi
Semiannual inflation

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

two years held

Amount purchased
$10,000.00
Fixed rate
1.2%
Semiannual inflation rate
1.5%
Months held
24

Current value$10,870.66

1.2 + 3.0 + 0.018, the official formula

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past five years there is no penalty

Amount purchased
$10,000.00
Fixed rate
1.2%
Semiannual inflation rate
1.5%
Months held
72

Current value$12,846.01

boundary

Open this example

Method and limits

What it assumes

  • A constant inflation component, which resets every six months in reality.

What it deliberately does not model

  • Annual purchase limits apply per person.
  • The inflation component changes twice a year and cannot be projected.
  • Interest is federally taxable and exempt from state and local tax.

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

Can I cash an I bond whenever I want?
Not in the first twelve months. Between one and five years you forfeit the last three months of interest, which is why the five year mark matters.
Is the composite rate just fixed plus inflation?
Nearly. The official formula adds a cross term, so it comes out slightly above simple addition.