Compound Interest Calculator
Use this free compound interest calculation tool to calculate interest and growth on your savings, or alternatively, the true cost of your debt.
Updated 9 July 2025
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Your Compound Interest Calculator is brought to you by Tiger Brokers (NZ) - helping New Zealanders turn compound interest theory into real investment returns.
You're here calculating compound interest - that's smart. However, our view is simple: while savings accounts and term deposits offer interest rates of 2% to 4%, the S&P 500 has averaged ~10% annually over the past 90 years. The difference? On $10,000 over 20 years (pre-tax):
That's three times more money from investing versus saving. We believe that too many New Zealanders prioritise dividends over growth, and this is holding them back. Our guide to the 10 Habits of Quiet Millionaires (and How You Can Follow Their Lead) provides further information on how to get ahead, as do many other resources on MoneyHub. Why We Like Tiger Brokers?
Exclusive MoneyHub Offer:
Ready to stop calculating and start compounding? Consider Investing with Tiger Brokers MoneyHub’s Editor Christopher Walsh says: "Tiger Brokers is aggressively priced for global investors. At a time when some platforms are raising fees or lacking innovation, Tiger Brokers is around half the cost of its nearest competitor for US stock trades. With an Auckland-based team, NZ regulation, and continued innovation (auto-invest, fractional shares, and its own TigerGPT chatbot), it’s a standout choice for cost-conscious investors and one that I use for US, China and Hong Kong share investments for the reasons outlined above". |
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Our Calculator:
Assumptions:
- The initial deposit is made today
- Interest is credited either monthly, quarterly, half yearly or annually, in line with standard New Zealand practice
- The results of this calculator are shown in future dollars
- No adjustment has been made for inflation
- Learn more with our 'interest rates explained' guide
Compound Interest Defined:
Compound interest is the addition of interest to the original amount of a loan or deposit, whereby interest calculated is re-invested into the original amount (or added to the loan) so that interest in the next period is then earned (or charged, if it is a loan) on the principal sum plus previously accumulated interest.
Compound Interest - A Win For Savers
Compound interest increases returns on savings and investments, but at the same time, increases the cost of debt. The calculator above shows the compounding returns of an investment or the true cost of compounding debt.
Compound interest works best as an investment tool - for example if you deposit $1,000 in the bank and earn 5% per year, with interest paid every month, the interest earned each month is re-invested with your original $1,000 and begins to earn its own interest. As a rule, the longer money is invested and interest added, the greater the compounding interest effect and the more money you will save.
Our calculator helps you to easily calculate compound interest in seconds, making financial decisions easier. To explain the concept of compound interest further, we have included some Frequently Asked Questions below.
Compound interest is the addition of interest to the original amount of a loan or deposit, whereby interest calculated is re-invested into the original amount (or added to the loan) so that interest in the next period is then earned (or charged, if it is a loan) on the principal sum plus previously accumulated interest.
Compound Interest - A Win For Savers
Compound interest increases returns on savings and investments, but at the same time, increases the cost of debt. The calculator above shows the compounding returns of an investment or the true cost of compounding debt.
Compound interest works best as an investment tool - for example if you deposit $1,000 in the bank and earn 5% per year, with interest paid every month, the interest earned each month is re-invested with your original $1,000 and begins to earn its own interest. As a rule, the longer money is invested and interest added, the greater the compounding interest effect and the more money you will save.
Our calculator helps you to easily calculate compound interest in seconds, making financial decisions easier. To explain the concept of compound interest further, we have included some Frequently Asked Questions below.
Frequently Asked Compound Interest Questions
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How do I earn Compound Interest?Both bank deposits and term investments earn interest, but the frequency with which they pay that interest affects the compound interest you can receive. For example, if you invest $1,000 with Bank ABC for 12 months and it pays 5.00% p.a. interest on a monthly basis, the interest you earn will compound every month. Alternatively, if the interest is only paid at the end of the 12 months, then there is no compounding interest.
Our guide to compound interest explains the concept in detail. |
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Which is better, 'Simple interest' or 'Compound interest'?When it comes to savings and investing, compound interest is better. This is because simple interest is calculated only on the original investment and paid at the end of the term, whereas compound interest is calculated on the original investment amount and the accumulated interest earned over previous periods. For this reason compound interest is known as "interest on interest.”
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What is the purpose of compound interest?Compound interest is attractive if you are earning it - bank deposits and term deposits usually pay compounded interest. However, if you are in debt, credit cards typically charge compound interest on the principal amount and the accumulated interest owed. This means that if you have an unpaid $1,000 credit card bill, you'll pay interest on the amount due. Whatever you don't pay will continue to be charged interest, so you will need to pay interest on the interest charged, as well as the original debt.
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What is an example of compound interest?In the example below, you can see a $10,000 investment earning 5.00% p.a. earns $500 of interest in year one, growing to $525 and $551.25 in years 2 and 3, respectively, because of the effect of compound interest. The interest earned from each period (I) is added to the opening balance (O) and increases each year as a result of the 5.00% interest rate being applied to a bigger balance.
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How often is interest compounded?The most common compound interest-earning investment is a bank account, and it is common for interest to be paid daily or at least monthly. For mortgages, personal loans and credit cards, interest is typically compounded monthly. Certain credit cards, like GEM Visa and the Q Card compound interest daily.
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