.g-fund-calculator-container {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 0 auto;
background: #ffffff;
border: 1px solid #e0e0e0;
border-radius: 8px;
padding: 25px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.g-fund-header {
text-align: center;
margin-bottom: 25px;
border-bottom: 2px solid #005ea2;
padding-bottom: 15px;
}
.g-fund-header h2 {
color: #005ea2;
margin: 0;
font-size: 24px;
}
.calc-row {
display: flex;
flex-wrap: wrap;
gap: 20px;
margin-bottom: 20px;
}
.calc-group {
flex: 1;
min-width: 200px;
background: #f8f9fa;
padding: 15px;
border-radius: 6px;
border: 1px solid #eee;
}
.calc-group h3 {
font-size: 16px;
color: #333;
margin-top: 0;
margin-bottom: 15px;
border-bottom: 1px solid #ddd;
padding-bottom: 5px;
}
.input-wrapper {
margin-bottom: 15px;
}
.input-wrapper label {
display: block;
font-size: 14px;
font-weight: 600;
color: #444;
margin-bottom: 5px;
}
.input-wrapper input {
width: 100%;
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box; /* Important for padding */
}
.input-wrapper input:focus {
border-color: #005ea2;
outline: none;
}
.calc-btn {
display: block;
width: 100%;
padding: 15px;
background-color: #005ea2;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background 0.3s;
margin-top: 10px;
}
.calc-btn:hover {
background-color: #00447a;
}
.result-box {
margin-top: 25px;
background: #eef5fc;
border: 1px solid #bbd4ea;
border-radius: 6px;
padding: 20px;
text-align: center;
display: none;
}
.result-value {
font-size: 32px;
font-weight: bold;
color: #005ea2;
margin: 10px 0;
}
.result-label {
font-size: 14px;
color: #555;
text-transform: uppercase;
letter-spacing: 1px;
}
.g-fund-article {
margin-top: 40px;
line-height: 1.6;
color: #333;
}
.g-fund-article h3 {
color: #005ea2;
margin-top: 30px;
}
.g-fund-article ul {
padding-left: 20px;
}
.g-fund-article li {
margin-bottom: 10px;
}
@media (max-width: 600px) {
.calc-row {
flex-direction: column;
}
}
function calculateGFundRate() {
// Get inputs using var
var v1 = parseFloat(document.getElementById('vol1').value) || 0;
var y1 = parseFloat(document.getElementById('yield1').value) || 0;
var v2 = parseFloat(document.getElementById('vol2').value) || 0;
var y2 = parseFloat(document.getElementById('yield2').value) || 0;
var v3 = parseFloat(document.getElementById('vol3').value) || 0;
var y3 = parseFloat(document.getElementById('yield3').value) || 0;
// Validation: Ensure we have at least some volume
var totalVolume = v1 + v2 + v3;
if (totalVolume <= 0) {
document.getElementById('resultBox').style.display = 'block';
document.getElementById('finalRate').innerHTML = "Invalid Volume";
document.getElementById('mathBreakdown').innerHTML = "Please enter positive outstanding volume numbers to calculate the weight.";
return;
}
// Calculate Weighted Sums
// Formula: Sum(Volume * Yield) / Total Volume
var weightedSum1 = v1 * y1;
var weightedSum2 = v2 * y2;
var weightedSum3 = v3 * y3;
var totalWeightedSum = weightedSum1 + weightedSum2 + weightedSum3;
var calculatedRate = totalWeightedSum / totalVolume;
// Monthly breakdown (G fund interest is accrued daily but often viewed monthly)
var monthlyRate = calculatedRate / 12;
// Display Results
document.getElementById('resultBox').style.display = 'block';
document.getElementById('finalRate').innerHTML = calculatedRate.toFixed(4) + "%";
document.getElementById('mathBreakdown').innerHTML =
"Based on a total outstanding volume of
." +
"The weighted average calculation mirrors the statutory requirement used by the U.S. Treasury.";
}
How Is the G Fund Rate Calculated?
The G Fund (Government Securities Investment Fund) is a unique investment option available exclusively to participants of the Thrift Savings Plan (TSP). Unlike other government bond funds that fluctuate in price based on interest rate changes, the G Fund is guaranteed to preserve capital while providing a rate of return based on a specific statutory formula. Understanding this calculation is key to predicting its performance.
The Statutory Formula
The G Fund's interest rate is set once a month by the U.S. Treasury. By law (5 U.S.C. ยง 8438(e)(2)), the rate is calculated as the weighted average yield of all outstanding Treasury notes and bonds with 4 or more years remaining to maturity.
This specific calculation method provides two distinct advantages:
- Long-term Rates: Because it includes bonds with long maturities (up to 30 years), the G Fund typically yields higher returns than short-term savings accounts or money market funds.
- Short-term Liquidity: Despite being based on long-term bonds, participants can trade in and out of the G Fund daily without penalty and without the risk of principal loss.
Step-by-Step Calculation Logic
To calculate the rate, the Treasury does not simply take an average of interest rates. They must weight the average based on the volume of debt outstanding. Here is how the math works, as simulated by the calculator above:
- Identify Securities: The Treasury lists all outstanding notes and bonds that will not mature for at least 4 years.
- Determine Volume: They record the dollar amount (par value) outstanding for each of these securities.
- Determine Yield: They record the yield-to-maturity for each security.
- Weighting: They multiply the volume of each security by its yield to determine its contribution to the total.
- Final Division: The sum of these weighted yields is divided by the total outstanding volume of all eligible securities.
Why Does the G Fund Rate Change?
The G Fund rate changes monthly based on the current market yields of U.S. Treasuries. Several economic factors influence these yields:
- Federal Reserve Policy: When the Fed raises the Federal Funds Rate, yields on newer Treasury notes generally rise, eventually pulling the G Fund rate up.
- Inflation Expectations: Higher inflation usually leads to higher bond yields as investors demand more return to offset purchasing power loss.
- Economic Growth: Strong economic data can push yields higher, while recession fears often push yields lower as investors flock to the safety of bonds.
G Fund vs. F Fund
It is important to distinguish the G Fund calculation from the F Fund. The F Fund tracks the Bloomberg U.S. Aggregate Bond Index. The F Fund's share price can drop if interest rates rise because existing bond prices fall. The G Fund, however, uses a special non-marketable security issued specifically to the TSP. Its principal is preserved mathematically, so the "calculation" only determines the interest earned, not the share price (which is always $1.00).