10.5% (Income up to $14,000)
17.5% (Income $14,001 – $48,000)
30.0% (Income $48,001 – $70,000)
33.0% (Income $70,001 – $180,000)
39.0% (Income over $180,000)
0% (Exempt/Non-Resident)
At Maturity (Simple Interest)
Paid Out Monthly
Paid Out Quarterly
Compounded Quarterly (Re-invested)
Gross Interest Earned:$0.00
Estimated Tax (RWT):$0.00
Net Interest (After Tax):$0.00
Total Maturity Value:$0.00
Note: Calculations assume the rate remains fixed for the entire term. "Compounded" assumes interest is added to the principal quarterly.
function calculateEarnings() {
// 1. Get input values
var principal = parseFloat(document.getElementById('investAmount').value);
var months = parseFloat(document.getElementById('termMonths').value);
var ratePercent = parseFloat(document.getElementById('interestRate').value);
var taxRatePercent = parseFloat(document.getElementById('taxRate').value);
var type = document.getElementById('payoutType').value;
// 2. Validate inputs
if (isNaN(principal) || principal <= 0) {
alert("Please enter a valid investment amount.");
return;
}
if (isNaN(months) || months <= 0) {
alert("Please enter a valid term length in months.");
return;
}
if (isNaN(ratePercent) || ratePercent < 0) {
alert("Please enter a valid annual interest rate.");
return;
}
// 3. Calculation Variables
var rateDecimal = ratePercent / 100;
var taxDecimal = taxRatePercent / 100;
var years = months / 12;
var grossInterest = 0;
var maturityValue = 0;
// 4. Logic Switch based on Payout Type
if (type === 'maturity' || type === 'monthly' || type === 'quarterly') {
// Simple Interest Formula: I = P * R * T
// Note: Even if paid monthly, the total gross interest over the term is roughly the same (ignoring days in month nuances for this estimation)
grossInterest = principal * rateDecimal * years;
maturityValue = principal + grossInterest;
}
else if (type === 'compound') {
// Compound Interest (Quarterly): A = P(1 + r/n)^(nt)
// n = 4 (Quarterly)
var n = 4;
var amount = principal * Math.pow((1 + rateDecimal / n), (n * years));
grossInterest = amount – principal;
maturityValue = amount;
}
// 5. Calculate Tax
var taxAmount = grossInterest * taxDecimal;
var netInterest = grossInterest – taxAmount;
// If interest is paid out during term, the maturity value is just Principal (usually),
// but for a "Total Value" perspective, we sum Principal + Net Interest received.
var finalTotalValue = principal + netInterest;
// 6. Formatting Helper
var formatMoney = function(num) {
return "$" + num.toLocaleString('en-NZ', { minimumFractionDigits: 2, maximumFractionDigits: 2 });
};
// 7. Update DOM
document.getElementById('grossInterestDisplay').innerHTML = formatMoney(grossInterest);
document.getElementById('taxDisplay').innerHTML = formatMoney(taxAmount);
document.getElementById('netInterestDisplay').innerHTML = formatMoney(netInterest);
document.getElementById('maturityValueDisplay').innerHTML = formatMoney(finalTotalValue);
// 8. Show Results
document.getElementById('results').style.display = 'block';
}
Understanding ASB Term Deposit Rates
When looking to grow your savings in New Zealand, ASB Term Deposits offer a low-risk investment option with a fixed return rate. Unlike a standard savings account where rates can fluctuate, a term deposit locks in your interest rate for a specific period, ranging from a few months to several years.
This calculator helps you estimate your potential returns by factoring in the principal investment, the term length, and critically, the Resident Withholding Tax (RWT) which impacts your final "money in hand".
How Term Deposit Interest is Calculated
The calculation of your return depends heavily on how the interest is paid out:
At Maturity: The most common option for short terms (less than 6 months). Interest is calculated on the principal and paid in a lump sum when the term ends.
Paid Out Regularity (Monthly/Quarterly): You receive the interest as income into a separate account. While this provides cash flow, you lose the benefit of compounding.
Compounding: For longer terms (usually 6 months+), you can choose to have interest added back to your principal (usually quarterly). This means you earn interest on your interest, resulting in a higher effective yield over time.
Resident Withholding Tax (RWT)
In New Zealand, interest earned on bank deposits is considered income and is taxed before it reaches your account. This is known as Resident Withholding Tax. The rate you select in the calculator should match your income tax bracket:
10.5%: If your annual income is $14,000 or less.
17.5%: For income between $14,001 and $48,000.
30.0%: For income between $48,001 and $70,000.
33.0%: For income between $70,001 and $180,000.
39.0%: For income over $180,000.
Key Investment Terms
Principal: The initial amount of money you deposit.
Term: The duration you agree to keep your money in the bank. Breaking a term deposit early usually incurs a fee or a reduction in interest earned.
p.a. (Per Annum): This stands for "per year." Even if you invest for 6 months, the rate shown is usually the annual rate, not the rate for those 6 months. For example, a 6% p.a. rate on a 6-month term pays effectively 3% gross.
Why Use This Calculator?
Banks often advertise the "Gross" interest rate. However, the actual amount landing in your pocket is the "Net" interest after tax. By using this tool, you can compare different term lengths and rates (e.g., a 9-month special vs. a 1-year standard rate) to see which option yields the best actual dollar return for your specific tax situation.