This calculator projects what an electronic I bond could be worth after a chosen number of whole months, and what you would receive if you cashed it then. It follows Treasury's savings bond regulation, 31 CFR part 359: a composite rate that never goes below zero, a value grown on a $25 unit and rounded to the cent each month, and, before five years, the loss of the last three months' interest, never taking the bond below what you paid.
It is a projection, not a quote. A real I bond takes a new inflation rate every six months from its own issue month, and nobody knows those future figures; the calculator applies the one six-month inflation rate you enter to every period, for up to 30 years.
No current I bond rate is printed here. The defaults ($10,000, a 1.00% fixed rate, a 1.20% six-month inflation rate, 30 months) are illustrative; the two rates are those of the worked example on the I bond interest rate page. TreasuryDirect publishes the real rates each 1 May and 1 November.
I bond value projector
Enter your bond’s fixed rate and an assumed six-month inflation rate. The defaults are illustrative, not current rates — TreasuryDirect publishes the real ones each May and November.
Uses Treasury’s own method from 31 CFR part 359: the composite-rate formula with its zero floor, values built on a $25 unit and rounded to the cent, each six-month value carrying into the next, and the loss of three months’ interest when a bond is cashed before five years, never below the purchase price. It applies one assumed inflation rate to every six-month period, so it is a projection. For a bond you already own, the value shown in your TreasuryDirect account is the authoritative figure. Educational estimate, not financial or tax advice.
What to enter, and where to find it
Four numbers, then Project value.
Purchase amount. From $25 to $10,000, to the cent, matching TreasuryDirect's "$25 minimum or any amount above that to the penny" and its limit of $10,000 of electronic I bonds a calendar year per Social Security or employer identification number. Outside that range the calculator asks you to change the figure.
Fixed rate. Your bond's own, set when it was bought and kept for life. For a bond you hold, look up its issue date in TreasuryDirect's I bond rate chart, which lists the fixed, inflation and combined rates for every issue period. For a new purchase, it is the fixed rate on TreasuryDirect's I bond interest rates page. The calculator refuses a negative fixed rate; the regulation says it is always 0.00% or more.
Six-month inflation rate. Your assumption. Enter the semiannual figure the formula takes, not the annualised one in Treasury's press releases, which is double and would count inflation twice. Negative figures are allowed: six-month deflation has happened.
Whole months held. From 0 to 360, counted from the issue date, the first day of the month in which Treasury received your money. A part month is rounded to the nearest whole month.
Why each bond's rate resets every six months from its own issue month, not on the announcement dates, is explained on the rate page.
How Treasury values an I bond
The calculator follows the regulation in four steps.
- The composite rate. TreasuryDirect's formula is "[Fixed rate + (2 x semiannual inflation rate) + (fixed rate x semiannual inflation rate)]", rounded to the nearest hundredth of a percentage point as in TreasuryDirect's own worked example. A negative result becomes zero ("zero will be the assumed composite rate"), and the result line says so.
- A $25 unit. "We base all calculations of interest on a $25 unit," says 31 CFR 359.19. Interest is added on the first of each month and compounds twice a year. Within each six-month period the unit is worth its starting value times one plus half the composite rate, raised to the months elapsed over six: the formula in 31 CFR 359.39, FV = PV × (1 + CR/2)^(m/6), rounded to the cent. Before that rounding, a full six months adds exactly half the composite rate.
- Scaling up. Under 31 CFR 359.55, an electronic bond is worth its purchase amount divided by 100, times the value of a $100 bond (four $25 units), rounded to the cent.
- The penalty. Cashed less than five years after issue, the bond is valued "as if the redemption date were three months earlier", but never below what you paid (31 CFR 359.7).
On a $10,000 bond each cent on the unit is $4, an effect the regulation says "can work to your slight advantage or disadvantage". Its own example uses a 2002 composite of 2.57%, history rather than an illustrative or current rate: a $25 unit reaches $25.32 in six months, so a $5,000 bond is worth $5,064, against $5,064.25 with the rate applied straight to $5,000. The calculator's $25-unit arithmetic reproduces that to the cent, though the tool itself shows no value before month 12.
Reading the result
The result opens with the composite rate your assumptions produce, then gives one of three answers.
- Under 12 months: "Not cashable yet". I bonds cannot be cashed in their first 12 months. TreasuryDirect waives this in declared disaster areas and, its FAQ says, "in some cases" of financial hardship; the calculator models neither, and it applies the 12-month rule to every bond, though I bonds issued before February 2003 could be cashed after six months. The lock is why the emergency-fund page calls I bonds a bad emergency fund.
- 12 to 59 months: the value after the penalty. The headline is what you would receive, never less than you paid; below it are the interest in that figure, the value with all its interest and what cashing then costs. TreasuryDirect's own figures work the same way: for bonds under five years old, "values shown in TreasuryDirect and the Calculator don’t include the last 3 months of interest". How to cash I bonds covers the redemption itself, partial cashing included.
- 60 months or more: the full value. The penalty "does not apply to bonds redeemed five years or more after the issue date".
A table follows for 12, 24, 36, 48, 60, 120, 240 and 360 months, with an asterisk on the four rows inside the penalty years. The 360-month row is marked final maturity: I bonds earn for 30 years, then stop. When I bonds mature covers where an electronic bond's money goes then, and why a paper bond stays cashable however old it is.
The defaults, worked through (illustrative)
Everything here is illustrative: $10,000, a 1.00% fixed rate, a 1.20% six-month inflation rate for the bond's whole life, cashed at 30 months. The formula gives 0.03412, which rounds to 3.41%. The $25 unit grows like this, and the bond follows it:
| Months | $25 unit | $100 bond | $10,000 bond, before any penalty |
|---|---|---|---|
| 0 | $25.00 | $100.00 | $10,000.00 |
| 6 | $25.43 | $101.72 | $10,172.00 |
| 12 | $25.86 | $103.44 | $10,344.00 |
| 18 | $26.30 | $105.20 | $10,520.00 |
| 24 | $26.75 | $107.00 | $10,700.00 |
| 27 | $26.98 | $107.92 | $10,792.00 |
| 30 | $27.21 | $108.84 | $10,884.00 |
Cashed at 30 months, the bond is valued as at month 27: you receive $10,792.00, or $792.00 of interest. With all 30 months it would be worth $10,884.00, so cashing then costs $92.00, about a tenth of the $884.00 earned. On its defaults the calculator shows $10,792.00, $792.00, $10,884.00 and $92.00.
The rounding is visible too. Applying 3.41% straight to $10,000 gives $10,882.07 at 30 months, $1.93 less than Treasury's method here, and months 28, 29 and 30 add $28.00, $32.00 and $32.00, because a $10,000 bond moves in $4 steps.
The calculator's table on the same inputs:
| Cashed at | Value shown | Three-month penalty applied |
|---|---|---|
| 12 months | $10,260.00 | Yes |
| 24 months | $10,608.00 | Yes |
| 36 months | $10,976.00 | Yes |
| 48 months | $11,352.00 | Yes |
| 60 months | $11,844.00 | No |
| 120 months | $14,024.00 | No |
| 240 months | $19,664.00 | No |
| 360 months, final maturity | $27,580.00 | No |
Waiting from month 59 ($11,708.00) to month 60 ($11,844.00) is worth $136.00 on these numbers: the penalty falls away and another month's interest arrives. Every figure in both tables rests on one assumed inflation rate applied to every six-month period; a real bond's inflation rate is reset every six months.
What the calculator does not do
It does not value a bond you own. It knows no real bond's rate history; a bond bought years ago has been through many inflation rates, and the calculator applies one. TreasuryDirect: "If you have a Series I electronic bond, you can see what it is worth in your TreasuryDirect account." That figure, which the regulation says already reflects the three-month penalty for a bond under five years old, is the authoritative one.
It does not price paper bonds. TreasuryDirect's own Savings Bond Calculator does, for paper Series EE, E and I bonds and savings notes, from the series, denomination and issue date. It gives the value today, past values, and future values only "through the current six-month interest period", with current and past rates, the next accrual date and the maturity date. It is "for paper savings bonds only" and will not "provide accurate results for the value of electronic bonds".
It does not compute tax. The interest it shows, what you receive less what you paid, is subject to federal income tax but not state or local income tax, under 31 U.S.C. 3124; federal estate, gift and excise taxes and state estate or inheritance taxes still apply. Under the cash method of accounting, which the IRS says most individual taxpayers use, you can report the interest yearly or defer it until the earlier of the year you cash or dispose of the bond and the year it matures; under an accrual method it is reported yearly. The rate page sets out both methods, and how to cash I bonds covers the tax form that follows and the education exclusion.
It does not forecast, model a partial redemption, or apply the disaster and hardship waivers of the 12-month lock.
EE bonds are a different calculation
A Series EE bond bought today earns a fixed rate and carries a promise an I bond does not: "in 20 years it will be worth at least twice what you paid for it", through "a one-time adjustment, if necessary". That top-up changes the arithmetic, so this calculator does not value EE bonds; EE bonds vs I bonds works out the doubling as an annual rate and what an I bond would need to match it. Treasury bills differ again: sold at a discount or at par and paid face value at maturity, as what Treasury bills are explains.
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