function calculateCD() {
var principal = parseFloat(document.getElementById('initialDeposit').value);
var apy = parseFloat(document.getElementById('apyRate').value) / 100;
var term = parseFloat(document.getElementById('termLength').value);
var unit = document.getElementById('termUnit').value;
var compoundFreq = parseFloat(document.getElementById('compounding').value);
if (isNaN(principal) || isNaN(apy) || isNaN(term) || principal <= 0 || apy < 0 || term <= 0) {
alert("Please enter valid positive numeric values.");
return;
}
// Convert term to years for the formula
var timeInYears = (unit === 'months') ? (term / 12) : term;
// Compound Interest Formula: A = P(1 + r/n)^(nt)
// Note: Since we are using APY, which already accounts for compounding,
// the most accurate simple calculation for APY is: Final = Principal * (1 + APY)^Years
// However, to reflect how banks calculate specific compounding periods:
var finalAmount = principal * Math.pow((1 + (apy / compoundFreq)), (compoundFreq * timeInYears));
var totalInterest = finalAmount – principal;
document.getElementById('finalBalance').innerText = '$' + finalAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('totalInterest').innerText = '$' + totalInterest.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
var unitLabel = (unit === 'months') ? (term === 1 ? 'month' : 'months') : (term === 1 ? 'year' : 'years');
document.getElementById('summaryText').innerText = "In " + term + " " + unitLabel + ", your initial deposit of $" + principal.toLocaleString() + " will grow to $" + finalAmount.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + " at an APY of " + (apy * 100).toFixed(2) + "%.";
document.getElementById('resultsArea').style.display = 'block';
}
Understanding Your CD APY and Returns
A Certificate of Deposit (CD) is one of the safest ways to grow your savings while enjoying a guaranteed rate of return. Unlike standard savings accounts, a CD requires you to leave your money untouched for a specific period, known as the "term." In exchange for this commitment, banks typically offer a higher Annual Percentage Yield (APY) than they do for flexible savings.
What is APY?
Annual Percentage Yield (APY) is the real rate of return earned on your deposit, taking into account the effect of compound interest. Unlike "simple interest," APY reflects how often interest is added to your balance. The more frequently interest compounds (daily vs. annually), the faster your money grows. Our calculator uses the compound interest formula to show exactly how much your initial deposit will be worth at the end of your term.
Key Factors Influencing Your CD Growth
Initial Deposit: The starting amount you lock into the CD. Generally, the more you deposit, the more interest you earn.
The Term: This is the duration of the investment. Common terms range from 6 months to 5 years. Long-term CDs usually offer higher APYs.
Compounding Frequency: Most modern high-yield CDs compound daily or monthly. Our calculator allows you to adjust this to match your bank's specific policy.
Example Calculations
Deposit Amount
APY
Term
Total Interest
$1,000
4.00%
12 Months
$40.74
$10,000
5.00%
24 Months
$1,051.63
$50,000
4.50%
5 Years
$12,615.42
Why Use a CD APY Calculator?
Using a dedicated CD calculator helps you compare different offers from various financial institutions. Even a 0.25% difference in APY can result in significant earnings over a multi-year term, especially on larger deposits. Additionally, it helps you visualize the cost of inflation; if your APY is lower than the inflation rate, your "real" purchasing power might decrease even though your balance is rising.
Pro Tip: Always check for "Early Withdrawal Penalties." Most CDs charge a fee—often 3 to 6 months of interest—if you take your money out before the term ends. Only deposit funds you are certain you won't need until the maturity date.