Series I Savings Bond Calculator
body {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
background-color: #f8f9fa;
color: #333;
line-height: 1.6;
margin: 0;
padding: 20px;
}
.calculator-container {
max-width: 800px;
margin: 30px auto;
background-color: #ffffff;
padding: 30px;
border-radius: 8px;
box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
border: 1px solid #dee2e6;
}
h1, h2 {
color: #004a99;
text-align: center;
margin-bottom: 20px;
}
.input-group {
margin-bottom: 20px;
display: flex;
flex-wrap: wrap;
gap: 15px;
align-items: center;
}
.input-group label {
flex: 1 1 150px;
font-weight: bold;
color: #004a99;
margin-bottom: 5px;
display: block;
}
.input-group input[type="number"] {
flex: 2 1 200px;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 4px;
font-size: 1rem;
box-sizing: border-box;
}
.input-group input[type="number"]:focus {
border-color: #004a99;
outline: none;
box-shadow: 0 0 0 3px rgba(0, 74, 153, 0.2);
}
button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #004a99;
color: white;
border: none;
border-radius: 5px;
font-size: 1.1rem;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 10px;
}
button:hover {
background-color: #003366;
}
.results-section {
margin-top: 30px;
padding-top: 20px;
border-top: 1px solid #eee;
}
.result-item {
margin-bottom: 15px;
font-size: 1.1rem;
color: #555;
}
.result-label {
font-weight: bold;
color: #004a99;
}
.result-value {
font-weight: bold;
color: #28a745;
font-size: 1.3rem;
}
.result-highlight {
background-color: #e6f7ff;
padding: 15px;
border-radius: 5px;
border-left: 5px solid #004a99;
text-align: center;
}
.result-highlight .result-value {
font-size: 1.8rem;
color: #004a99;
}
.article-content {
margin-top: 40px;
line-height: 1.8;
color: #444;
}
.article-content h2 {
text-align: left;
margin-bottom: 15px;
color: #004a99;
}
.article-content p, .article-content ul, .article-content li {
margin-bottom: 15px;
}
.article-content ul {
padding-left: 25px;
}
.article-content li {
margin-bottom: 8px;
}
.article-content strong {
color: #004a99;
}
@media (max-width: 600px) {
.input-group {
flex-direction: column;
align-items: stretch;
}
.input-group label {
flex-basis: auto;
margin-bottom: 8px;
}
.input-group input[type="number"] {
flex-basis: auto;
width: 100%;
}
.calculator-container {
padding: 20px;
}
}
Series I Savings Bond Calculator
Your Projected Savings
Total Principal Invested:
—
Total Estimated Earnings:
—
Projected Total Value:
—
Understanding Series I Savings Bonds
Series I Savings Bonds, or "I Bonds," are a type of U.S. savings bond that earns interest based on a combination of a fixed rate and an inflation rate. They are designed to protect your investment from inflation, meaning their value increases over time as the cost of living rises. I Bonds are a popular choice for conservative investors looking for a safe way to grow their savings and preserve purchasing power.
How I Bonds Work
The interest rate on an I Bond has two components:
- Fixed Rate: This rate is set when the bond is issued and remains the same for the life of the bond (up to 30 years). It reflects the real rate of return investors are earning above inflation.
- Inflation Rate: This rate is adjusted twice a year (in May and November) based on changes in the Consumer Price Index for All Urban Consumers (CPI-U). It's designed to keep pace with inflation, protecting the purchasing power of your savings.
The combined rate is calculated using a specific formula: Composite Rate = [Fixed Rate + (2 * Semiannual Inflation Rate) + (Fixed Rate * Semiannual Inflation Rate)]. For simplicity in this calculator, we use an average annual inflation rate and apply it semiannually.
Calculator Logic Explained
This calculator estimates the future value of your I Bonds based on your initial investment, regular contributions, the duration you plan to hold them, the fixed rate of the bond, and an estimated average annual inflation rate.
- Initial Deposit: The principal amount you invest at the beginning.
- Monthly Contribution: The amount you add to your I Bond investment each month.
- Number of Years: The total period you intend to hold the bonds. I Bonds earn interest for up to 30 years.
- Average Annual Inflation Rate (%): Your projection for how much prices will increase on average each year. This directly impacts the variable part of the I Bond's interest rate.
- Fixed Rate (%): The fixed component of the I Bond's interest rate, determined at issuance and unchanging for the bond's life.
The calculator simulates the growth year by year, compounding the interest earned based on the combined rate. The total principal invested is the sum of all your contributions. Total earnings are the difference between the final projected value and the total principal.
Key Features and Considerations
- Tax Deferral: Interest earned on I Bonds is not taxed at the federal level until you redeem the bond, or until it reaches final maturity (30 years), whichever comes first. State and local income taxes are also not applicable.
- Maturity: I Bonds earn interest for 30 years.
- Redemption Rules: You must hold an I Bond for at least 12 months. If redeemed before 5 years, you forfeit the last 3 months of interest.
- Purchase Limits: Individuals can purchase up to $10,000 in electronic I Bonds per calendar year via TreasuryDirect. Additional amounts can be purchased with tax refunds.
- Risk: I Bonds are backed by the U.S. government and are considered among the safest investments available. The primary risk is not earning as much as other investments might, particularly during periods of low inflation or low fixed rates.
Use this calculator to project potential growth and understand the impact of different inflation and fixed rate scenarios on your I Bond investments over time. Remember that the inflation rate is variable and actual returns may differ from projections.
function calculateIbond() {
var initialDeposit = parseFloat(document.getElementById("initialDeposit").value);
var monthlyContribution = parseFloat(document.getElementById("monthlyContribution").value);
var years = parseInt(document.getElementById("years").value);
var annualInflationRate = parseFloat(document.getElementById("annualInflationRate").value) / 100; // Convert to decimal
var fixedRate = parseFloat(document.getElementById("fixedRate").value) / 100; // Convert to decimal
// Input validation
if (isNaN(initialDeposit) || initialDeposit < 0) initialDeposit = 0;
if (isNaN(monthlyContribution) || monthlyContribution < 0) monthlyContribution = 0;
if (isNaN(years) || years <= 0) years = 1;
if (isNaN(annualInflationRate) || annualInflationRate < -1) annualInflationRate = 0; // Inflation can't realistically be less than -100%
if (isNaN(fixedRate) || fixedRate < 0) fixedRate = 0; // Fixed rate cannot be negative
var totalPrincipalInvested = initialDeposit + (monthlyContribution * 12 * years);
var currentBalance = initialDeposit;
var totalEarnings = 0;
// Simulate year by year growth
for (var y = 0; y =0)
if (interestThisYear < 0) interestThisYear = 0;
annualInterestEarned = interestThisYear;
// Add monthly contributions for the year
currentBalance += (monthlyContribution * 12);
currentBalance += annualInterestEarned;
totalEarnings = currentBalance – totalPrincipalInvested;
if (totalEarnings {
calculateIbond();
});