Tools · Live MAS, CPF and bank rates
Compound interest calculator with monthly top-ups
What your savings and monthly top-ups grow to in Singapore dollars, at today’s real rates, after inflation and fees, with the working shown.
In short
Compound interest is interest earned on earlier interest. $10,000 to start plus $500 a month at 4% for 20 years comes to $205,613, of which $75,613 is interest. The rate matters more than how often it compounds: today CPF’s Ordinary Account pays 2.5% and a 6-month T-bill about 1.88%, and you can test each above.
The same plan at today’s real rates
Most compound interest calculators ask you to guess a rate. These are the rates on offer in Singapore today, each run on the plan in the calculator above. The bars redraw as you change it.
You would put in $130,000 over 20 years. To buy as much then as that money buys now, you need about $161,980.
Each bar holds today’s rate flat for the whole period, which no real rate does. Tap any rate button in the calculator to load it. The list is sorted by result and is not advice on what suits you.
Will your money really compound?
The formula assumes interest stays in and earns more interest. In Singapore, much of it doesn’t unless you put it back yourself.
| Option | How interest arrives | Compounds by itself? | Monthly top-ups? |
|---|---|---|---|
| Fixed deposit2.3% for 12 months | Paid at the end of the term. | Only if you renew with the interest, at whatever rate applies then. Check your bank’s terms. | No: each placement has its own minimum. |
| T-billAbout 1.88% for 6 months | You pay less than face value and get the full amount at maturity. | No. The money comes back and you apply again. | Not really: $1,000 minimum, then multiples of $1,000. |
| Savings Bond2.39% 10-year average | A coupon every 6 months, paid to your bank account. | No. Coupons reach your bank. To compound, you buy more yourself. | In $500 lots, up to $200,000, with a $2 fee a time. |
| CPF OA and SA2.5% and 4% | Worked out monthly, credited yearly. | Yes, once a year. | By CPF’s rules and limits. See the CPF calculator. |
| STI ETF (ES3)8.59% a year since 2002, past | Distributions twice a year, at the manager’s discretion, plus the price moving. | No. The published return assumes you reinvest them. | One share at a time, at your broker’s fees. |
Rates read today from our trackers. Rules from MAS, CPF Board and State Street’s factsheet, re-read on 7 Nov 2026.
What moves your number most
One change at a time to the plan above, biggest effect first.
The cost of waiting
Starting 10 years later, with the same plan and the same end date, leaves you $117,080 short.
Your plan at every rate and length
Your starting amount and top-ups at each rate and length. Tap a figure to load it into the calculator.
| Rate | 5 yrs | 10 yrs | 20 yrs | 30 yrs | 40 yrs |
|---|---|---|---|---|---|
| 1% | |||||
| 2% | |||||
| 3% | |||||
| 4% | |||||
| 5% | |||||
| 6% | |||||
| 8% | |||||
| 10% |
Year by year
Your plan at the end of each year. “Today’s money” is the balance after inflation.
| End of | Put in | Interest | Balance | Today’s money |
|---|---|---|---|---|
| Year 1 | $16,000 | $519 | $16,519 | $16,195 |
| Year 2 | $22,000 | $1,303 | $23,303 | $22,398 |
| Year 3 | $28,000 | $2,363 | $30,363 | $28,612 |
| Year 4 | $34,000 | $3,712 | $37,712 | $34,840 |
| Year 5 | $40,000 | $5,359 | $45,359 | $41,083 |
| Year 6 | $46,000 | $7,319 | $53,319 | $47,345 |
| Year 7 | $52,000 | $9,602 | $61,602 | $53,628 |
| Year 8 | $58,000 | $12,223 | $70,223 | $59,935 |
| Year 9 | $64,000 | $15,195 | $79,195 | $66,267 |
| Year 10 | $70,000 | $18,533 | $88,533 | $72,628 |
| Year 11 | $76,000 | $22,251 | $98,251 | $79,020 |
| Year 12 | $82,000 | $26,366 | $108,366 | $85,446 |
| Year 13 | $88,000 | $30,892 | $118,892 | $91,907 |
| Year 14 | $94,000 | $35,847 | $129,847 | $98,408 |
| Year 15 | $100,000 | $41,248 | $141,248 | $104,950 |
| Year 16 | $106,000 | $47,114 | $153,114 | $111,535 |
| Year 17 | $112,000 | $53,464 | $165,464 | $118,168 |
| Year 18 | $118,000 | $60,316 | $178,316 | $124,850 |
| Year 19 | $124,000 | $67,692 | $191,692 | $131,583 |
| Year 20 | $130,000 | $75,613 | $205,613 | $138,372 |
What really happened with $500 a month
A calculator holds one rate for ever. Real rates don’t hold still: the 6-month T-bill’s cut-off ran from 0.2% to 4.4% over these 90 months. Today’s yield of about 1.88%, held flat, would have shown $48,349. Rolling real auctions gave $49,125.
6-month T-bills, rolled CPF OA CPF SA Keeping up with prices
Tap or hover on the chart to read a value.
| Money went into | Ended at | Gain on $45,000 put in |
|---|---|---|
| 6-month T-bills, rolled every time | $49,125 | +$4,125 |
| CPF Special Account | $52,277 | +$7,277 |
| CPF Ordinary Account | $49,389 | +$4,389 |
| Keeping up with prices | $49,483 | +$4,483 |
Our sums from MAS’s auction prices, CPF Board’s rate for each quarter and SingStat’s CPI. T-bills: six rungs, one bought each month at that month’s first auction price and rolled every 6 months; a rung part-way through counts its gain pro rata; the $1,000 minimum is ignored. CPF: each month’s money earns from the next month and interest joins the balance every December. No fees. “Keeping up with prices” is each $500 grown by the CPI to Nov 2026. The record starts when 6-month auctions have run without a gap in our data.
Does daily or monthly compounding matter?
Less than most people think. A bank that compounds more often pays a little more at the same headline rate, and the gap is small next to the rate itself, the time and fees. Here is your plan at each frequency.
| Interest joins the balance | Effective a year | Your plan ends at | Against monthly |
|---|---|---|---|
| Daily | 4.081% | $205,775 | +$162 |
| Monthly | 4.074% | $205,613 | – |
| Quarterly | 4.060% | $205,283 | −$330 |
| Half-yearly | 4.040% | $204,796 | −$817 |
| YearlyHow CPF does it | 4.000% | $203,855 | −$1,758 |
“Effective a year” is the rate once compounding is counted, so it compares offers with different frequencies.
How a month works here
- Start of the month: a top-up set to “start” joins the balance, so it earns this month.
- During the month: interest is worked out on the balance, at the yearly rate ÷ 12.
- On the crediting date: that interest joins the balance and starts to earn too. Every month, every quarter, every half-year or every year, as you choose.
- End of the month: a top-up set to “end” joins, and earns from next month. CPF works the same way: money received in a month starts to earn the month after.
The compound interest formula
For a lump sum, A = P(1 + r/n)nt. A is what you end up with, P is the starting amount, r is the yearly rate as a decimal, n is how many times a year interest is added, and t is the years.
Say $5,000 at 3% compounded half-yearly for 4 years. r/n is 0.03 ÷ 2 = 0.015, and nt is 2 × 4 = 8. So A = 5,000 × 1.0158 = $5,632.46, and the interest is $632.46. The Homework button above loads this example with every step shown.
Monthly top-ups add a second part: M × ((1 + r/n)nt − 1) ÷ (r/n), where M is the top-up and n is 12. In Excel or Google Sheets, =FV(rate/12, months, -topup, -start) gives the same answer. Open “Show the working” under your result for both, with your own numbers.
Simple against compound interest
Simple interest is paid on the starting amount only. Compound interest is paid on the starting amount and on earlier interest. The gap starts small, then grows.
| After | Simple | Compound | Compounding adds |
|---|---|---|---|
| 1 year | $10,400 | $10,400 | $0 |
| 2 years | $10,800 | $10,816 | $16 |
| 5 years | $12,000 | $12,167 | $167 |
| 10 years | $14,000 | $14,802 | $802 |
| 20 years | $18,000 | $21,911 | $3,911 |
| 30 years | $22,000 | $32,434 | $10,434 |
The Rule of 72
A quick way to see how long money takes to double: divide 72 by the rate. MoneySense gives the example of 4%, about 18 years. The rule is close for ordinary rates and drifts at very low ones.
| Rate a year | Rule of 72 | Exact |
|---|---|---|
| 1% | 72.0 years | 69.7 years |
| 2% | 36.0 years | 35.0 years |
| 2.5% | 28.8 years | 28.1 years |
| 3% | 24.0 years | 23.4 years |
| 4% | 18.0 years | 17.7 years |
| 5% | 14.4 years | 14.2 years |
| 6% | 12.0 years | 11.9 years |
| 8% | 9.0 years | 9.0 years |
| 10% | 7.2 years | 7.3 years |
| 12% | 6.0 years | 6.1 years |
Exact years = log 2 ÷ log (1 + rate), with interest added yearly.
Which rate should you use?
For money you won’t risk, use a rate you can get today, from the buttons in the calculator. Then try a lower one, because today’s fixed deposit and T-bill rates are not locked in for 20 years.
For shares, no one can give you a rate, so use a past return only as a rough guide and try several. The STI ETF below shows why: the yearly return depends heavily on which years you measure. A fund’s price can fall, and in a bad year your balance will drop, which a smooth calculator never shows.
| Over the last | A year, after fees |
|---|---|
| 1 year | 36.48% |
| 3 years | 25.83% |
| 5 years | 17.6% |
| 10 years | 11.03% |
| Since April 2002 | 8.59% |
State Street SPDR Straits Times Index ETF (ES3), to 30 Sep 2026, from its factsheet, checked 7 Nov 2026: net of fees, in S$, with distributions reinvested. State Street says past performance is not necessarily indicative of future performance. Before 22 June 2026 the fund tracked the index on a price basis, and since then on a total return basis.
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Questions people ask
How do I work out compound interest with monthly deposits?
Add two parts: what the starting amount grows to, and what the top-ups grow to. The formula is under The compound interest formula, and the calculator does both and shows the steps with your numbers. Any top-up made later has less time to grow, so the last deposits earn almost nothing.
How much will $500 a month be worth?
At 4% compounded monthly, with nothing to start, $500 a month comes to $73,625 after 10 years, $183,387 after 20 years and $347,025 after 30 years. You would have put in $60,000, $120,000 and $180,000. At 2.5%, the 20-year figure is $155,487.
How long does it take to reach $1 million?
From nothing, $1,000 a month takes 36 years 9 months at 4%, 30 years at 6% and 25 years 7 months at 8%. $2,000 a month takes 24 years 7 months at 4% and 21 years at 6%. Those are amounts on paper: in today’s money $1 million will buy much less by then.
Is monthly compounding better than yearly?
Yes, at the same headline rate, but only slightly. The table above shows the gap on your plan. A higher rate almost always beats a better frequency.
Does CPF interest compound?
CPF Board works interest out monthly and credits it once a year, so it compounds yearly. On $100,000 left for 30 years at 4%, that gives $324,340. A calculator set to monthly compounding shows $331,350, which is $7,010 too much. Set “Interest joins the balance” to Yearly, or tap a CPF rate, which does it for you. Extra interest on the first $60,000 is on top, and the CPF calculator includes it.
What is the effective interest rate?
The rate you really get in a year once compounding is counted. 4% compounded monthly is 4.07% a year. It lets you compare offers that compound differently. The frequency table gives it for your rate.
Do I pay tax on the interest?
Interest that individuals earn on deposits with banks and licensed finance companies in Singapore is not taxed. IRAS’s page covers other kinds of interest. The calculator takes no tax off.
Does this include inflation?
Yes. Every answer also gives the balance in today’s money, starting at Singapore’s average inflation over the last 10 years. You can change it under the extra settings, and set it to 0 to switch it off.
Why does my bank’s figure differ?
Banks may work interest out daily, credit it on set dates, and pay tiers or bonuses this calculator doesn’t know about. Promotional rates also end. Use this for planning, and your bank’s statement for the exact sum.
Is this financial advice?
No. It is arithmetic on the numbers you enter, plus published rates. Numbers.sg sells no financial product.
The checks
These run each time the page is built: our month-by-month engine against the closed formulas, against two worked examples published by others, and against itself when solving backwards.
| Check | Expected | Ours | OK |
|---|---|---|---|
| Excel’s FV sum: $10,000 + $500 a month, 4% monthly, 20 years | $205,613.13 | $205,613.13 | ✓ |
| The same, top-ups at the start of each month | $206,224.42 | $206,224.42 | ✓ |
| Lump sum, yearly: $10,000 × 1.05^10 | $16,288.95 | $16,288.95 | ✓ |
| Lump sum, half-yearly: $5,000 × 1.015^8 | $5,632.46 | $5,632.46 | ✓ |
| Lump sum, quarterly: $1,000 × 1.0125^120 | $4,440.21 | $4,440.21 | ✓ |
| Lump sum, daily: $1,000 × (1 + 5%/365)^3650 | $1,648.66 | $1,648.66 | ✓ |
| SmartCalculator’s published example: $205,613 | $205,613.00 | $205,613.00 | ✓ |
| Saxo’s published example: $200 a month, 8%, 30 years, $298,072 | $298,072.00 | $298,072.00 | ✓ |
| How much a month: solving for $300,000 reaches it | At least $300,000.00 | $300,053.00 | ✓ |
| How long: solving for $300,000 reaches it | At least $300,000.00 | $301,682.00 | ✓ |
| What rate: solving for $300,000 reaches it | At least $300,000.00 | $300,059.00 | ✓ |
How it works
- The sum runs month by month. Each month’s interest is the balance × the rate ÷ 12. It joins the balance on each crediting date: every month, quarter, half-year or year. Daily compounding uses the monthly equivalent of 365 compoundings a year. A top-up joins at the start or the end of its month, and a yearly lump sum at the end of each year.
- A fee comes off the rate, as a percentage of your balance each year. Inflation divides the balance by (1 + inflation)^years. It starts at Singapore’s average over the last 10 years, from SingStat’s CPI, and you can change it.
- Solving: the monthly amount is exact, because the result grows in a straight line with it, and it is rounded up to the dollar. The time is the first month the total reaches your goal. The rate is found by halving the gap 50 times, then rounded up to 0.01%.
- The rate buttons use today’s reading from our fixed deposit, T-bill, Savings Bond, CPF and cash account pages, and hold it flat. Each also sets the compounding that fits it. Real rates move, so the back-test shows what moving rates did. ES3’s figures are copied by hand from its factsheet each month.
- Tests: the checks above run each time the page is built. Before going live, browser and server sums matched on 600 cases, and the engine matched the closed formulas on 864 cases.
- The calculator runs in your browser and nothing you type is sent anywhere. This is arithmetic, not advice, and a rate held flat for decades is a simplification.
Disclosure: the editor, Jeremiah Say, holds Singapore Savings Bonds and T-bills, bought on the same terms as anyone else, and has no fixed deposits. Numbers.sg is not paid by MAS, CPF Board, any bank or anyone selling these products, and there are no affiliate links on this page.
Contains information from SGS auction results and issuance calendar accessed on 7 Nov 2026 from the Monetary Authority of Singapore website, which is made available under the terms of the MAS Terms of Use of Datasets. Numbers.sg is independent and is not endorsed by MAS.
Changes to this page
New: a compound interest calculator for Singapore dollars. Enter a start, a monthly top-up, a rate and a length, or tap today’s fixed deposit, T-bill, Savings Bond or CPF rate, and see the balance in dollars and in today’s money, with the working. It can also solve for the monthly amount, the time or the rate, and it compares your plan at every rate on offer. A back-test shows what $500 a month really did in rolled T-bills and CPF since June 2019, and that table is a new download, compound-backtest.csv. Work out your savings