Calculate the estimated value of your I Bonds based on purchase date and principal amount.
Estimated Value After 1 Year
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Understanding U.S. Savings I Bonds
U.S. Savings I Bonds are a type of savings bond issued by the U.S. Treasury. They offer a return composed of two parts: a fixed rate (which remains the same for the life of the bond) and an inflation rate, which is adjusted semi-annually based on the Consumer Price Index for all Urban Consumers (CPI-U). This dual-rate structure makes I Bonds an attractive option for protecting savings from inflation.
How I Bonds Accrue Interest
I Bonds earn interest for 30 years. The interest rate is a combination of a fixed rate and an inflation rate. The fixed rate is set when the bond is issued and never changes. The inflation rate is adjusted every six months (May and November) based on changes in the CPI. The composite rate is calculated using a formula that gives a weighted average of the fixed and inflation rates.
The formula for the composite annual interest rate is:
Composite Rate = Fixed Rate + (2 * Semiannual Inflation Rate) + (Fixed Rate * Semiannual Inflation Rate)
For simplicity in this calculator, we are estimating the value after one full year, assuming the interest earned in the first six months is compounded with the interest earned in the second six months. The calculator uses the most recent available semi-annual inflation rates and a placeholder fixed rate to provide an estimate.
Key Features and Considerations:
Inflation Protection: The primary benefit of I Bonds is their ability to keep pace with inflation, preserving purchasing power.
Tax Deferral: Interest earned is not taxed at the federal level until the bond is redeemed, reaches maturity, or is otherwise disposed of. State and local taxes do not apply.
Maturity: I Bonds earn interest for 30 years. They can be redeemed after 12 months, but if redeemed before 5 years, you forfeit the last 3 months of interest.
Purchase Limits: Individuals can purchase up to $10,000 electronically per Social Security number per calendar year. Paper I Bonds can be purchased with tax refunds, up to an additional $5,000.
Rates: The fixed rate is set at issuance. The inflation rate changes every six months. You can find the current rates on the TreasuryDirect website.
How This Calculator Works:
This calculator provides an *estimated* value of your I Bond after one year. It requires you to input the month and year of purchase, and the principal amount.
Important Notes:
The calculator uses recent fixed and inflation rates for illustrative purposes. Actual I Bond rates change and can be found on the official TreasuryDirect website.
The calculation assumes interest compounds semi-annually.
The calculator estimates the value after exactly 12 months from your purchase date. It does not account for the 3-month interest penalty if redeemed before 5 years.
This is a simplified model; actual bond value may vary slightly due to the exact timing of rate changes and the precise CPI calculations used by the Treasury.
function calculateI Bonds() {
var purchaseMonth = parseInt(document.getElementById("purchaseMonth").value);
var purchaseYear = parseInt(document.getElementById("purchaseYear").value);
var principalAmount = parseFloat(document.getElementById("principalAmount").value);
var resultDisplay = document.getElementById("result-value");
resultDisplay.innerText = "–";
resultDisplay.className = ""; // Reset class
// — Rate Data (Example: Rates as of recent periods. These are illustrative and change. For precise calculations, always refer to TreasuryDirect.) —
// Data structure: { year: { month: { fixed_rate, inflation_rate_q1, inflation_rate_q2 } } }
// Inflation rates are typically for Jan-Jun (Q1) and Jul-Dec (Q2) of a given year.
// For calculation purposes, we'll use the rate effective for the *period* the bond is held.
// Let's use simplified semi-annual rates for demonstration.
var rateData = {
2023: {
jan_jun: { fixed_rate: 0.20, inflation_rate_semiannual: 2.11 }, // ~4.22% composite annual (example)
jul_dec: { fixed_rate: 0.20, inflation_rate_semiannual: 1.67 } // ~3.37% composite annual (example)
},
2024: {
jan_jun: { fixed_rate: 0.40, inflation_rate_semiannual: 1.83 }, // ~3.71% composite annual (example)
jul_dec: { fixed_rate: 0.40, inflation_rate_semiannual: 1.37 } // ~2.76% composite annual (example)
},
// Add more years as needed for realistic examples
2025: {
jan_jun: { fixed_rate: 0.45, inflation_rate_semiannual: 1.50 },
jul_dec: { fixed_rate: 0.45, inflation_rate_semiannual: 1.60 }
}
};
// — End Rate Data —
// Input Validation
if (isNaN(purchaseMonth) || purchaseMonth 12) {
alert("Please enter a valid purchase month (1-12).");
return;
}
if (isNaN(purchaseYear) || purchaseYear new Date().getFullYear() + 1) { // I Bonds started in 1998
alert("Please enter a valid purchase year (e.g., 1998 or later).");
return;
}
if (isNaN(principalAmount) || principalAmount 12) {
effectivePeriod1EndMonth -= 12;
effectivePeriod1EndYear += 1;
}
var rateSet1 = getRatesForPeriod(effectivePeriod1StartYear, effectivePeriod1StartMonth, rateData);
if (!rateSet1) {
resultDisplay.innerText = "Rate data unavailable for this period.";
return;
}
// Calculate interest for the first 6 months (simple interest for the period)
var annualRate1 = calculateCompositeRate(rateSet1.fixed_rate, rateSet1.inflation_rate_semiannual);
var interestFirst6Months = principalAmount * (annualRate1 / 200); // Divide by 2 because annual rate is given, and we need interest for half a year.
// The principal for the next 6 months includes the interest earned.
var principalForSecondHalf = principalAmount + interestFirst6Months;
// Determine the rate for the second 6 months (12 months from purchase)
var effectivePeriod2StartMonth = effectivePeriod1EndMonth;
var effectivePeriod2StartYear = effectivePeriod1EndYear;
var effectivePeriod2EndMonth = effectivePeriod2StartMonth + 6;
var effectivePeriod2EndYear = effectivePeriod2StartYear;
if (effectivePeriod2EndMonth > 12) {
effectivePeriod2EndMonth -= 12;
effectivePeriod2EndYear += 1;
}
var rateSet2 = getRatesForPeriod(effectivePeriod2StartYear, effectivePeriod2StartMonth, rateData);
if (!rateSet2) {
resultDisplay.innerText = "Rate data unavailable for this period.";
return;
}
// Calculate interest for the second 6 months (simple interest for the period)
var annualRate2 = calculateCompositeRate(rateSet2.fixed_rate, rateSet2.inflation_rate_semiannual);
var interestSecond6Months = principalForSecondHalf * (annualRate2 / 200);
calculatedValue = principalForSecondHalf + interestSecond6Months;
resultDisplay.innerText = "$" + calculatedValue.toFixed(2);
resultDisplay.className = "positive"; // Style for positive values
}
function getRatesForPeriod(year, month, rateData) {
var ratesForYear = rateData[year];
if (!ratesForYear) return null;
// Determine which semi-annual period the month falls into.
// Month 1-6 is the first period, Month 7-12 is the second.
if (month >= 1 && month = 7 && month <= 12) {
return ratesForYear.jul_dec;
}
return null; // Should not happen with valid month input
}
function calculateCompositeRate(fixedRatePercent, semiannualInflationRatePercent) {
// Formula: Composite Rate = Fixed Rate + (2 * Semiannual Inflation Rate) + (Fixed Rate * Semiannual Inflation Rate)
// Rates are given in percentages, so divide by 100 for calculation.
var fixed = fixedRatePercent / 100;
var inflation = semiannualInflationRatePercent / 100;
var compositeAnnualRate = fixed + (2 * inflation) + (fixed * inflation);
// Convert back to percentage for display/use in interest calculation
return compositeAnnualRate * 100;
}
// Optional: Add a listener for Enter key press for convenience
document.addEventListener("keypress", function(event) {
if (event.key === "Enter" && document.activeElement.id !== "principalAmount") { // Prevent trigger if last input is focused
calculateI Bonds();
} else if (event.key === "Enter" && document.activeElement.id === "principalAmount") {
calculateI Bonds();
}
});