I Bond Calculator
This I bond calculator estimates what a Series I savings bond will be worth when you cash it, including the early withdrawal penalty and federal tax. It starts with the current 4.26% rate for bonds bought through October 31, 2026, then lets you choose how much inflation to expect after that.
Estimate only. Interest compounds every six months, as the Treasury does, with monthly accrual in between. Real values depend on future inflation and are calculated by the Treasury in $25 units, so they may differ by a few dollars. State and local tax do not apply.
Your I bond, year by year
This table updates with your inputs. “If cashed” subtracts three months of interest for years 1 through 4.
| Year | Bond value | If cashed | Interest you keep |
|---|---|---|---|
| 1 | $10,430.54 | $10,321.20 | $321.20 |
| 2 | $10,879.61 | $10,765.56 | $765.56 |
| 3 | $11,348.02 | $11,229.06 | $1,229.06 |
| 4 | $11,836.59 | $11,712.51 | $1,712.51 |
| 5 | $12,346.20 | $12,346.20 | $2,346.20 |
| 10 | $15,242.87 | $15,242.87 | $5,242.87 |
Current I bond rate: 4.26% through October 31, 2026
| Bonds bought | Fixed rate | Composite rate (first 6 months) |
|---|---|---|
| May 1 to Oct. 31, 2026 | 0.90% | 4.26% |
| Nov. 1, 2025 to Apr. 30, 2026 | 0.90% | 4.03% |
| From Nov. 1, 2026 | Announced by the Treasury on November 1, 2026 | |
The 4.26% rate combines the 0.90% fixed rate with a six-month inflation rate of 1.67%, based on the change in the Consumer Price Index from October 2025 to March 2026. We will update this page when the November rates are announced.
How I bond interest works
An I bond has two parts to its rate. The fixed rate is set when you buy and never changes. The inflation rate changes every six months, based on the Consumer Price Index. The Treasury combines them into a composite rate:
- Interest is added to the bond every six months, so it compounds.
- Your bond’s rate changes every six months from its issue month, not on a calendar date. A bond bought in October gets a new rate each April and October.
- If inflation turns negative, the composite rate can drop, but never below zero. Your bond’s value never goes down.
- Bonds are dated the first day of the month you buy, so a bond bought on October 30 earns interest for all of October.
What changes on November 1, 2026
On November 1, the Treasury sets a new fixed rate for bonds bought over the next six months and a new inflation rate based on prices from March to September 2026. The September inflation report, due in mid-October, gives the last piece of the inflation rate. The fixed rate is set by the Treasury and is harder to predict; it has tended to move with real yields on Treasury inflation-protected securities.
If you buy by October 31, you lock in 0.90% fixed for 30 years and earn 4.26% for six months, then switch to the new inflation rate. If you wait, you get whatever the new rates are. With long-term Treasury yields at their highest levels since 2002, many investors watch the November fixed rate closely. Our guide to rising bond yields explains what higher yields mean for savers.
I bond rules to know before you buy
| Rule | Details |
|---|---|
| Purchase limit | $10,000 per person per calendar year in electronic bonds |
| Minimum | $25, then any amount to the penny |
| Where to buy | Only at TreasuryDirect.gov, not through banks or brokers |
| Lock-up | Cannot be cashed in the first 12 months |
| Early penalty | Lose the last 3 months of interest if cashed before 5 years |
| Earns interest for | 30 years |
| Taxes | Federal tax only; state and local tax exempt; can be deferred until you cash it |
Because of the 12-month lock-up, do not put your emergency fund into I bonds until you have enough cash set aside elsewhere.
I bonds vs. T-bills vs. CDs
| I bond | Treasury bill | CD | |
|---|---|---|---|
| Current rate | 4.26% (6 months) | About 4.21% (13 weeks) | Up to about 4.40% (1 year) |
| Inflation protection | Yes | No | No |
| Access | Locked 12 months | Sell any day at market price | Penalty to withdraw early |
| State income tax | Exempt | Exempt | Taxed |
| Yearly limit | $10,000 | None | None |
I bonds shine when you worry about inflation and can leave the money alone for at least a year, ideally five. T-bills and CDs pay a known rate and are easier to reach. Compare exact numbers with our Treasury bill calculator and CD calculator.
Worked example: $10,000 in October 2026
- First 6 months at 4.26%$10,213.00
- Value after 1 year (inflation stays at 3.34%)$10,430.54
- Cash out at 1 year, minus 3 months’ interest$10,321.20
- Value after 5 years, no penalty$12,346.20
- Federal tax at 22% on $2,346.20 of interest−$516.16
If inflation is higher, the bond earns more; if it falls, the bond earns less. The 0.90% fixed rate means you always earn a little more than inflation.
Frequently asked questions
What is the I bond rate right now?
I bonds bought from May 1 through October 31, 2026 earn a composite rate of 4.26% for their first six months. That is a 0.90% fixed rate, which lasts for the life of the bond, plus an inflation rate of 1.67% for six months. The Treasury announces new rates on November 1, 2026.
How much will a $10,000 I bond be worth in 5 years?
If inflation stayed at today's pace, about $12,346.20, earning about $2,346.20 in interest. The real amount depends on inflation over the next five years, because the inflation part of the rate resets every six months.
Can I cash out an I bond early?
You cannot cash an I bond in the first 12 months. After that you can redeem it any time, but if you cash it before five years you lose the last three months of interest. After five years there is no penalty.
How much can I invest in I bonds each year?
Each person can buy up to $10,000 in electronic I bonds per calendar year through TreasuryDirect, starting at $25. Spouses each have their own limit, and you can buy for a child or as a gift for another person.
Are I bonds taxed?
I bond interest is subject to federal income tax but exempt from state and local income tax. You can report the interest each year or wait until you cash the bond or it matures after 30 years. Interest may be tax-free if you use it for qualified higher education costs and meet the income limits.
Should I buy I bonds before November 1, 2026?
Buying by October 31 locks in the current 0.90% fixed rate for 30 years and 4.26% for the first six months. Bonds bought from November 1 get the new rates, which could be higher or lower depending on inflation from March to September 2026 and the new fixed rate. Nobody knows the new rate in advance.
Sources and how we calculated
Current and previous rates are from the Treasury’s Series I savings bond rates page and its May 1, 2026 announcement, as reported by CNBC, with the fixed and inflation components from Tipswatch. The calculator uses the Treasury’s composite rate formula, rounds the composite rate to two decimals, compounds every six months and accrues interest monthly within each period.
This calculator is for educational purposes only and is not investment or tax advice. Future I bond rates depend on inflation and on fixed rates the Treasury has not yet announced. We do not recommend buying or selling any security.