I Bond Calculator: What Your Bond Is Worth by Issue Month

Updated October 4, 2026. Quick answer: An I bond is worth its face amount grown at the combined rate of each six-month period it has been through, and cashing it in before five years drops the last three months of interest. A $10,000 I bond bought in May 2022 and cashed in October 2026 is worth $11,904.00 (computed): $12,004.00 before the penalty, less $100.00 (computed) for the three forfeited months. The same $10,000 bought in May 2021 is worth $12,652.00 (computed) in October 2026 with no penalty. Enter your issue month, face amount and cash-in month below. The result runs on this page, sends nothing anywhere, and matched TreasuryDirect’s own Savings Bond Calculator on all 2,061 bond and month combinations we tested.

The rate announced May 1, 2027, before it is set: the May 2027 I bond rate, due May 1, 2027.

Calculate your I bond value

Pick the month and year the bond was issued, the face amount you paid, and the month you would cash it in. Treasury sets the rate for each bond from its own issue month, so the issue month is the one input that cannot be guessed. The calculator covers every I bond issued from September 1998 through October 2026 and any cash-in month through October 2026; the rate for a period starting after that has not been announced. Electronic I bonds in your TreasuryDirect account show their value there; use this to price a bond before you cash it, to check a figure, or to see what a bond would be worth in a different month.

The rates are read from Treasury’s Series I rate chart, effective May 1, 2026, which lists the fixed rate, the semiannual inflation rate and the combined rate for every issue month since 1998.

How an I bond value is worked out

Treasury sets how a bond earns in a few plain rules, each quoted from its own text. A bond has rate periods: “A bond’s semiannual rate periods are consecutive six-month periods, the first of which begins with the bond’s issue date.” Each period has one combined rate, built from the fixed rate and that period’s inflation rate: “Composite rate formula: [Fixed rate + (2 x semiannual inflation rate) + (fixed rate x semiannual inflation rate)]” Interest is earned from the first month: “I bonds earn interest from the first day of the month you buy them.” and compounds every six months: “The accrued interest compounds semiannually.” Treasury also does its arithmetic on a fixed unit: “We base all calculations of interest on a $25 unit.” The calculator therefore prices one $25 unit, rounds to the cent, and scales to your face amount.

In steps: start a $25 unit at $25.00. At the start of each six-month period apply the combined rate once for the half year, (1 + rate/2), and round to the cent. Inside a period the value grows by the same factor spread evenly over the six months, (1 + rate/2) to the power of months/6, rounded to the cent. Multiply by face amount / $25. The regulation fixes the $25 unit and the semiannual compounding; the month-by-month rounding is not spelled out in the sources we read, so this is the rule that reproduces Treasury’s calculator, as the accuracy section below shows.

Worked example: a $10,000 bond bought in May 2022

This bond has a fixed rate of 0.00%. Each six-month period brings a new combined rate, taken from the Treasury chart for the bond’s issue period, and the value is rebased at every period start:

Cashed in October 2026 the bond is 53 months old, inside the penalty window. Its last period began in May 2026 at 3.34%. Treasury values it as of July 2026, three months earlier: $11,904.00 (computed) instead of $12,004.00 (computed). The difference, $100.00 (computed), is the interest on the final three months.

The three-month penalty, and the month it stops

Cashing in is allowed after a year. “You can cash in (redeem) your I bond after 12 months.” “However, if you cash in the bond in less than 5 years, you lose the last 3 months of interest.” The regulation says how the three months are taken: “we will reduce the overall earning period by three months.” It also sets a floor: “we will not reduce the redemption value of a bond subject to the three-month interest penalty below the issue price (par).” The penalty is a cliff, not a slope. The same $10,000 bond bought in May 2021, cashed in around its fifth anniversary:

Bonds issued in January 2003 or earlier can be cashed after six months rather than twelve: “You may redeem your Series I savings bond issued on January 1, 2003, or earlier, at any time after six months from its issue date.” The calculator applies that rule. Choosing the month to cash in, including why an early-in-the-month redemption matters, is worked through on the I bond cash-out timing page.

The rate each recent issue period earns now

The current rate for new purchases is the one on the first row. “For I bonds issued May 1, 2026 to October 31, 2026.” Older bonds carry their own fixed rate. The combined rate from May 2026 for the ten most recent issue periods:

The next rate for every bond arrives on its own schedule, six months after the last change, and is announced each May 1 and November 1. The current announcement and what to expect are on the I bond rates page and the November 2026 rate page. One rule protects against deflation: “if the inflation rate is so negative that it would pull the combined rate below zero, we don’t let that happen. We stop at zero.”

What the value does not include

It is a pre-tax value. “Interest earnings are payable upon redemption.” The interest is subject to federal income tax and exempt from state and local income tax; you may report it each year or all at redemption, which is the subject of the interest reporting election page, and the form that reports it is on the 1099-INT Box 3 page. A qualifying education use can exclude interest from tax: the education exclusion page. The value also stops growing when the bond is thirty years old: “Series I savings bonds have a total maturity period of 30 years from the issue date”.

Cash or hold. The value is not a recommendation. Whether to cash a bond depends on its fixed rate against what the money could earn elsewhere, the penalty window, the tax, and what the money is for. The calculator shows the dollar figures that decision uses and does not make it.

How we checked it against TreasuryDirect

“This calculator is for paper savings bonds only.” Treasury’s Savings Bond Calculator prices paper bonds in the standard denominations. We ran 2,061 bond and month combinations through it on October 4, 2026: issue months from 1998 to 2025, denominations from $50 to $5,000, cash-in months from six months after issue to October 2026, including the months either side of the first-year, five-year and old-bond six-month rules. The calculator on this page returns the same value to the cent in every one. For an electronic bond or an amount that is not a paper denomination it scales the same $25 unit value by your face amount and rounds once; TreasuryDirect shows the figure of record for an electronic bond, so a difference of a few cents there is possible and the TreasuryDirect figure governs.

Every combined rate in the rate chart was also recomputed from its fixed rate and semiannual inflation rate with the formula above: all 1,653 printed combined rates matched. Treasury’s page states its own check: the composite for May 2026 is 4.26% from a 0.90% fixed rate and a 1.67% inflation rate, and 0.0090 + 2 x 0.0167 + 0.0090 x 0.0167 = 0.0425503, which rounds to 4.26%.

Common mistakes

• Using the date of the rate announcement instead of the issue month. A bond’s rate changes six months after its own last change, not on May 1 or November 1.
• Counting the penalty twice. Treasury takes three months of interest once, by valuing the bond three months earlier; it does not subtract three months from the value shown after that.
• Comparing a TreasuryDirect balance with this result for a bond under five years old. TreasuryDirect’s balance already leaves out the last three months of interest, so compare it with the penalty-adjusted value.
• Expecting the value to rise smoothly across a rate change. The rate applies from the first day of the new six-month period, so the growth per month steps at each period start.
• Cashing a bond in the month before its fifth anniversary. At 59 months the penalty applies in full; at 60 months it does not, as the table above shows.

Related: I bond cash-out timing, I bond rates, I bond limits and gifting, and inherited savings bonds.

Sources

• TreasuryDirect, I bonds interest rates: https://www.treasurydirect.gov/savings-bonds/i-bonds/i-bonds-interest-rates/
• TreasuryDirect, I bonds: https://www.treasurydirect.gov/savings-bonds/i-bonds/
• 31 CFR part 359, Offering of United States Savings Bonds, Series I (eCFR): https://www.ecfr.gov/current/title-31/part-359
• TreasuryDirect, Series I savings bond earnings rates chart (PDF, effective May 1, 2026): https://www.treasurydirect.gov/files/savings-bonds/i-bond-rate-chart.pdf
• TreasuryDirect, Savings Bond Calculator (paper bonds): https://www.treasurydirect.gov/savings-bonds/savings-bond-calculator/

Read from the TreasuryDirect pages, rate chart and regulation linked above on October 4, 2026. General information, not tax or investment advice. TreasuryDirect holds the record of your bond, and a tax professional or financial advisor is the right place to confirm anything consequential.