The Promotional Impact:
Without the promotional boost, you would have earned $0.00.
The promotion earned you an extra $0.00.
Understanding Marcus CD Rate Promotions
Marcus by Goldman Sachs is widely recognized for its high-yield Certificates of Deposit (CDs). One of the unique features that savvy savers utilize is the promotional rate structure, often available through referral bonuses or limited-time offers. This calculator is specifically designed to handle the complexity of "split-rate" periods, where a promotional APY (Annual Percentage Yield) applies for a specific duration (e.g., 3 months) before reverting to the standard rate for the remainder of the CD term.
The "Referral Bonus" Mechanic
A common promotion with Marcus is the Referral Bonus. When you refer a friend (or are referred), you often receive an APY Boost (typically +1.00%) on your Online Savings Account or specific CD products for a set period, usually 3 months.
Calculating the earnings for this isn't as simple as just adding 1% to the annual rate, because the boost expires before the CD matures (assuming a term longer than 3 months). Our calculator splits the timeline into two phases:
Phase 1 (Promotional Period): Your principal earns interest at the Base Rate + Boost Rate.
Phase 2 (Standard Period): The new balance (Principal + Phase 1 Interest) earns interest at the Base Rate for the remaining months.
How to Use This Calculator
To accurately project your earnings with a Marcus CD promotion:
Deposit Amount: Enter the total cash you intend to invest.
CD Term: Enter the full length of the CD in months (e.g., 12 months, 18 months).
Standard APY: Input the current non-promotional rate listed on the Marcus website.
APY Boost: If you have a referral code or a special offer, enter the added percentage (e.g., 1.00). If not, enter 0.
Boost Duration: Enter how many months the higher rate lasts. For referral bonuses, this is typically 3 months.
Formula Used
Marcus CDs typically compound interest daily. We use the standard compound interest formula adapted for two time periods:
A = P * (1 + r/n)^(n*t)
Where n is 365 (daily compounding). We calculate the balance after the promotional months, then use that accumulated total as the principal for the remaining months at the standard rate.
Frequently Asked Questions
Do Marcus CDs compound daily or monthly?
Marcus CDs generally compound interest daily and credit it to your account monthly. This results in a slightly higher effective yield compared to monthly compounding.
What is the difference between APY and Interest Rate?
The Interest Rate is the annualized percentage based on the principal. The APY (Annual Percentage Yield) includes the effect of compound interest. This calculator uses APY as the input, converting it back to a nominal rate for precise daily calculations.
function calculateMarcusCD() {
// 1. Get Inputs
var deposit = parseFloat(document.getElementById('mcdDeposit').value);
var termMonths = parseFloat(document.getElementById('mcdTerm').value);
var baseApy = parseFloat(document.getElementById('mcdBaseAPY').value);
var compoundingFreq = parseFloat(document.getElementById('mcdCompounding').value);
// Optional Promo Inputs
var promoBoost = parseFloat(document.getElementById('mcdPromoBoost').value);
var promoDuration = parseFloat(document.getElementById('mcdPromoDuration').value);
// 2. Validation
if (isNaN(deposit) || isNaN(termMonths) || isNaN(baseApy)) {
alert("Please enter valid numbers for Deposit, Term, and Base APY.");
return;
}
// Defaults if empty
if (isNaN(promoBoost)) promoBoost = 0;
if (isNaN(promoDuration)) promoDuration = 0;
// 3. Logic Setup
// Convert APY to Nominal Rate for calculation if needed,
// but for daily compounding close approximation, using APY directly in standard formula is common consumer practice.
// However, strictly: APY = (1 + r/n)^n – 1. So r = n * ((APY + 1)^(1/n) – 1).
// Let's implement strict conversion for accuracy.
function getNominalRate(apyPercent, n) {
var decimalApy = apyPercent / 100;
return n * (Math.pow((1 + decimalApy), (1/n)) – 1);
}
// Logic for Split Calculation
// Period 1: Promo
// Period 2: Standard
var effectivePromoDuration = Math.min(promoDuration, termMonths);
var remainingDuration = termMonths – effectivePromoDuration;
// Rates
var totalPromoApy = baseApy + promoBoost;
var nominalPromoRate = getNominalRate(totalPromoApy, compoundingFreq);
var nominalBaseRate = getNominalRate(baseApy, compoundingFreq);
// Time in years for formula
var time1 = effectivePromoDuration / 12;
var time2 = remainingDuration / 12;
// — Calculate With Promotion —
// Balance after Period 1
var balance1 = deposit * Math.pow((1 + nominalPromoRate / compoundingFreq), (compoundingFreq * time1));
// Balance after Period 2 (using balance1 as principal)
var finalBalanceWithPromo = balance1 * Math.pow((1 + nominalBaseRate / compoundingFreq), (compoundingFreq * time2));
var totalInterestWithPromo = finalBalanceWithPromo – deposit;
// — Calculate Without Promotion (Baseline) —
// Entire term at base rate
var timeTotal = termMonths / 12;
var finalBalanceBase = deposit * Math.pow((1 + nominalBaseRate / compoundingFreq), (compoundingFreq * timeTotal));
var totalInterestBase = finalBalanceBase – deposit;
// Effective Blended APY Calculation
// (FinalBalance / Principal)^(1/Years) – 1
var yearsTotal = termMonths / 12;
var blendedApy = 0;
if (yearsTotal > 0) {
blendedApy = (Math.pow((finalBalanceWithPromo / deposit), (1 / yearsTotal)) – 1) * 100;
}
// 4. Update UI
// Format Currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
document.getElementById('resMaturity').innerText = formatter.format(finalBalanceWithPromo);
document.getElementById('resInterest').innerText = formatter.format(totalInterestWithPromo);
document.getElementById('resEffectiveAPY').innerText = blendedApy.toFixed(2) + "%";
document.getElementById('resBaseInterest').innerText = formatter.format(totalInterestBase);
var difference = totalInterestWithPromo – totalInterestBase;
// Ensure difference is not negative due to floating point rounding if 0 boost
if(difference < 0) difference = 0;
document.getElementById('resDifference').innerText = formatter.format(difference);
// Show Results
document.getElementById('mcdResult').style.display = "block";
}