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font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 25px;
border: 1px solid #ddd;
border-radius: 8px;
background-color: #f9f9f9;
color: #333;
}
.bond-calc-container h2 {
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margin-bottom: 25px;
}
.bond-input-group {
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flex-direction: column;
}
.bond-input-group label {
margin-bottom: 8px;
font-weight: 600;
font-size: 14px;
}
.bond-input-group input, .bond-input-group select {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
}
.bond-calc-btn {
grid-column: span 2;
padding: 12px;
background-color: #27ae60;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
}
.bond-calc-btn:hover {
background-color: #219150;
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.bond-result-area {
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padding: 20px;
border-radius: 4px;
border-left: 5px solid #27ae60;
margin-top: 20px;
}
.bond-result-area h3 {
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.bond-article {
margin-top: 40px;
line-height: 1.6;
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text-align: left;
border-bottom: 2px solid #eee;
padding-bottom: 10px;
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.bond-article h3 {
color: #2c3e50;
margin-top: 25px;
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@media (max-width: 600px) {
.bond-calc-form {
grid-template-columns: 1fr;
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grid-column: span 1;
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Savings Bonds Growth Calculator
How to Calculate Your Savings Bonds Value
United States Savings Bonds are a secure investment backed by the full faith and credit of the U.S. government. Whether you hold Series I or Series EE bonds, understanding how they accrue interest is vital for long-term financial planning. This calculator helps you estimate the future value of your bonds based on current rates and compounding periods.
Series I Savings Bonds
Series I bonds are designed to protect your purchasing power from inflation. Their earnings rate is a combination of a fixed rate and a semiannual inflation rate. Interest is added to the bond every month and compounded semiannually. This means every six months, the interest earned in the previous period is added to the principal, and new interest is calculated on that larger amount.
Series EE Savings Bonds
Series EE bonds issued since May 2005 earn a fixed rate of interest. A unique feature of the Series EE bond is the Treasury's guarantee that the bond will double in value if held for 20 years. If the accumulated interest doesn't result in the bond doubling, the Treasury makes a one-time adjustment at the 20-year mark to fulfill this promise.
Calculation Example
If you purchase a Series I bond for $1,000 at an annual composite rate of 4.00% and hold it for 10 years:
- Principal: $1,000
- Compounding: Semiannual (2 times per year)
- Formula: $1,000 * (1 + 0.04/2)^(2 * 10)
- Projected Value: Approximately $1,485.95
Key Considerations
Interest on savings bonds is subject to federal income tax but exempt from state and local income taxes. If you use the bond proceeds for qualified higher education expenses, you may be able to exclude the interest from your federal income tax. Also, remember that bonds must be held for at least one year, and cashing them in before five years results in a penalty of the last three months of interest.
function calculateBondValue() {
var series = document.getElementById('bondSeries').value;
var principal = parseFloat(document.getElementById('bondPrincipal').value);
var rate = parseFloat(document.getElementById('bondRate').value) / 100;
var years = parseFloat(document.getElementById('bondYears').value);
var resultDiv = document.getElementById('bondResult');
if (isNaN(principal) || isNaN(rate) || isNaN(years) || principal <= 0 || years < 0) {
resultDiv.style.display = 'block';
resultDiv.innerHTML = "
Error
Please enter valid positive numbers for all fields.";
return;
}
// Savings bonds compound semiannually
var periodsPerYear = 2;
var totalPeriods = years * periodsPerYear;
var ratePerPeriod = rate / periodsPerYear;
// Compound interest formula: A = P(1 + r/n)^(nt)
var futureValue = principal * Math.pow((1 + ratePerPeriod), totalPeriods);
// Special logic for Series EE 20-year doubling guarantee
var isDoubled = false;
if (series === 'EE' && years >= 20) {
var doubledPrincipal = principal * 2;
if (futureValue < doubledPrincipal) {
futureValue = doubledPrincipal;
isDoubled = true;
}
}
var totalInterest = futureValue – principal;
resultDiv.style.display = 'block';
var output = "
Estimated Results
";
output += "
Final Bond Value: $" + futureValue.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + "";
output += "
Total Interest Earned: $" + totalInterest.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + "";
if (isDoubled) {
output += "
* Includes the Treasury's 20-year doubling guarantee for Series EE.";
}
if (years < 5) {
output += "
Note: Bonds cashed before 5 years incur a 3-month interest penalty (not deducted in this estimate).";
}
resultDiv.innerHTML = output;
}