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Compound Interest Calculator
Watch Your Money Multiply
The most powerful force in personal finance β free to use, no sign-up required. Calculate compound interest with monthly contributions across any time horizon and see exactly how much of your wealth comes from investing vs. from the market doing the work for you.
5
Compounding frequencies
30yr
Milestone projections
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The fundamentals
What Is Compound Interest β and Why Does It Matter So Much?
Compound interest is the process by which the interest you earn on an investment itself earns interest in subsequent periods. Unlike simple interest β which only ever calculates interest on your original principal β compound interest creates a snowball effect where your returns accelerate over time. Albert Einstein reportedly called it the “eighth wonder of the world,” and while that attribution is disputed, the mathematical reality is not: compound interest is the single most important concept in personal finance.
The difference between simple and compound interest is dramatic over long time horizons. If you invest S$10,000 at 7% simple interest for 30 years, you earn S$21,000 in interest. But at 7% compound interest (compounded monthly), the same S$10,000 grows to over S$81,000 β almost four times more. That extra S$60,000 is pure compounding at work.
The core insight: In the early years, compound interest feels slow. Most of your portfolio is money you contributed. But past a tipping point β usually around year 15 to 20 β the interest you earn on your previous interest begins to outpace your own contributions. By year 30, for most investors, the market has contributed more wealth than they ever deposited themselves.
Our compound interest calculator handles this formula for you automatically β including the more complex version that accounts for regular monthly contributions (PMT), which is the real-world scenario most investors face. You don’t need to understand the maths. You just need to understand the outcome.
How to use it
How to Use This Compound Interest Calculator
This free compound interest calculator gives you a complete picture of your investment growth with five inputs. Here’s exactly what each one means and how to fill it in accurately:
1
Starting amount (principal)
Enter the lump sum you’re investing today. This could be existing savings, a bonus, an inheritance, or any amount you have ready to invest right now. If you’re starting from zero, enter 0 β the calculator will still project your growth from monthly contributions alone.
2
Annual interest rate
Enter your expected annual return as a percentage. For a globally diversified equity index fund, 7% is a commonly used historical average after inflation. For a savings account or fixed deposit, use the actual advertised rate. For bonds or mixed portfolios, 4β5% is a reasonable middle estimate. Be realistic β overestimating this number produces dangerously optimistic projections.
3
Investment period (years)
How many years will you leave this money invested? This is the most powerful input in the entire calculator. Increasing your time horizon by even 5 years can add more to your final balance than doubling your monthly contribution. Use your target retirement age minus your current age as a starting point.
4
Monthly contribution
How much will you add to your investment every month? This is where regular investing β sometimes called dollar-cost averaging β comes in. Even a modest monthly contribution, maintained consistently over decades, has an enormous impact on your final balance. Enter the amount you can realistically commit to every single month.
5
Compounding frequency
How often does your interest compound? Monthly is standard for most investment accounts and unit trusts. Daily compounding (used by some savings accounts) produces slightly higher returns. Annual compounding is used in some bond calculations. For most investors, the difference between monthly and daily is small β focus more on the rate and time horizon.
Compounding frequency explained
Does Compounding Frequency Really Matter?
Yes β but perhaps less than you think. The table below shows the final value of a S$10,000 investment at 7% annual interest over 20 years under each of the five compounding frequencies this calculator supports. The difference between annual and daily compounding is less than 2% β meaningful, but far less important than choosing a higher-return investment or investing for longer.
| Compounding frequency |
Periods/year |
Final value (20yr) |
Extra vs annual |
| Annually | 1Γ | S$38,697 | β |
| Bi-annually | 2Γ | S$39,296 | +S$599 |
| Monthly (most common) | 12Γ | S$40,064 | +S$1,367 |
| Weekly | 52Γ | S$40,160 | +S$1,463 |
| Daily | 365Γ | S$40,178 | +S$1,481 |
The takeaway: choose monthly compounding as your default, and spend your energy on increasing your contribution or extending your time horizon β both have a far bigger impact than chasing daily compounding.
The tipping point
When Does Interest Overtake Your Contributions?
The most eye-opening aspect of compound interest is the tipping point β the moment when the interest you’ve earned begins to earn more than you’re personally depositing. The chart below shows this for a S$500/month investor at 7% annual return. Notice how the green bar (interest earned) grows from almost nothing to dwarf the blue bar (your contributions) by year 30.
Year
Portfolio breakdown
Total value
Based on S$500/month at 7% annual return, monthly compounding. By year 30, the market has contributed over 75% of the total portfolio β you personally only deposited S$180,000 of the S$735,234 final balance.
Who benefits
Who Should Use a Compound Interest Calculator?
This free compound interest calculator is useful for anyone making decisions about saving, investing, or planning for the future. Here are the most common use cases:
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Young professionals starting out
Even S$200βS$300 a month at 25 can grow to a life-changing sum by 55. Use this calculator to see exactly how much your early start is worth in dollar terms.
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Parents investing for children
Planning a university fund or head-start investment? Enter your child’s age and calculate what a regular monthly contribution grows to by the time they turn 18 or 21.
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Savers comparing accounts
Run the calculator twice with different interest rates to quantify the actual dollar difference between a 1.5% savings account and a 4% fixed deposit over 5 years.
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Retirement planners
Input your current retirement savings and monthly contribution to project your balance at 55, 60, or 65. Then use our FI Number Calculator to check if it’s enough.
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Freelancers & self-employed
Without employer pension contributions, building wealth is entirely up to you. See how much discipline around a monthly investment habit can produce over 20β30 years.
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Singapore investors (CPF + SRS)
Model the growth of your SRS account, voluntary CPF top-ups, or unit trust investments. Enter the actual projected return and see your long-term wealth picture.
Investment tips
6 Ways to Maximise the Power of Compound Interest
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Start as early as possible
Time is the most powerful variable in the compound interest formula. Starting at 25 vs 35 doesn’t just give you 10 more years β it can double your final balance. Every year you wait is expensive.
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Automate monthly contributions
Set up a standing order on payday so the money leaves before you can spend it. Consistency of contribution is more important than size. S$300 every month beats S$3,600 once a year (compounding is more frequent).
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Minimise fees relentlessly
A 2% annual fund fee vs a 0.2% index ETF fee doesn’t sound like much β but over 30 years it can cost you 40% of your final portfolio. Use this calculator with different rates to see the staggering impact.
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Never interrupt compounding
Withdrawing from an investment account β even temporarily β breaks the compounding chain. The years immediately before withdrawal are the most valuable, not the least. Let it compound uninterrupted.
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Increase contributions when income rises
Every time you get a pay rise, commit to increasing your monthly investment before lifestyle inflation absorbs it. Redirecting just 50% of a raise into investments dramatically accelerates your compounding curve.
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Use tax-advantaged accounts first
For Singapore residents, voluntary CPF top-ups and SRS contributions compound in tax-advantaged wrappers β your effective return is higher because you keep more. Max these out before taxable investment accounts.
FAQ
Frequently Asked Questions About Compound Interest
What is the difference between compound interest and simple interest?
Simple interest is calculated only on your original principal β so S$10,000 at 7% simple interest always earns S$700/year, forever. Compound interest is calculated on your principal plus all the interest you’ve already earned. So in year two, you earn interest on S$10,700, not S$10,000. This self-reinforcing mechanism is what creates exponential growth over time. The longer the time horizon, the wider the gap between the two.
What annual return rate should I use in the calculator?
It depends entirely on what you’re investing in. For a globally diversified equity index fund (like MSCI World or S&P 500), 7% is a commonly cited long-run historical average after inflation. For a Singapore fixed deposit or savings account, use the actual advertised rate (typically 2β4%). For a balanced portfolio of 60% equities and 40% bonds, 5β6% is a reasonable estimate. The key is to be honest rather than optimistic β using 10% to feel good about your projections and then investing in 3% savings bonds will leave you with a significant shortfall.
Does the calculator account for inflation?
The calculator shows nominal (not inflation-adjusted) returns by default. To get inflation-adjusted (real) projections, simply subtract the inflation rate from your expected return before entering it. For example, if you expect 7% returns and 2.5% inflation, enter 4.5% as your rate. This gives you the growth in purchasing power rather than just in dollar terms β a more honest picture of your real-world wealth.
How does the growth multiplier work?
The growth multiplier shown in the calculator results is simply the future value divided by everything you personally contributed (principal + all monthly deposits). A multiplier of 4.2Γ means that for every S$1 you put in over the investment period, you end up with S$4.20. The higher this number, the more the market has done the work for you versus your own savings effort. Multipliers above 3Γ typically require 20+ years of consistent investing.
What’s the best compounding frequency for investments?
For most real-world investment accounts, monthly compounding is the standard and the most practically relevant. Daily compounding is used by some high-yield savings accounts and produces slightly more growth, but the difference is usually less than 0.1% per year. What matters far more is the annual return rate and how long you stay invested. Choose “Monthly” as your default and don’t spend time optimising compounding frequency.
How much should I invest each month to reach my goal?
This calculator works in reverse too β enter your target future value and work backward. Try different monthly contribution amounts until the milestone table shows your goal year. As a rough guide: to accumulate S$500,000 over 25 years at 7% annual return, you need to invest approximately S$750/month. For S$1,000,000 over the same period, approximately S$1,500/month. The key is starting as early as possible to let compounding do the heavy lifting.
Is compound interest used in savings accounts in Singapore?
Yes β most Singapore savings accounts, fixed deposits, and investment products use compound interest. DBS Multiplier, OCBC 360, UOB One, and most unit trusts all compound your returns. CPF balances also compound β your Ordinary Account earns a minimum 2.5% compounded annually, while the Special Account earns 4%. This makes CPF one of the best low-risk compounding vehicles available to Singaporeans, particularly for the long-term retirement savings component.
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β οΈ Disclaimer: This compound interest calculator is provided for general educational and informational purposes only and does not constitute financial, investment, or tax advice. Projections assume a constant rate of return and regular contributions β real investments fluctuate, and returns are never guaranteed. Past performance does not guarantee future results. Figures do not account for fees, taxes, or inflation unless you adjust the inputs yourself. Always consult a licensed financial adviser before making investment decisions.
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