How much will your money grow? Points Frog's compound interest calculator takes a starting amount, what you add each month or year, a rate and how often it compounds. It then splits the result into what you put in and what interest earned.
Its opening example shows how lopsided that split gets. Put in $10,000, add $500 at the end of each month and earn 7% a year, compounded monthly. After 30 years you would have $691,150. Of that, $190,000 is your own money and $501,150, or 73%, is interest.
Compound interest is interest earned on interest. $10,000 at 5% a year earns $500 in the first year and $525 in the second, because the second year's interest is paid on $10,500. After 10 years it reaches $16,289 compounded yearly, against $15,000 with simple interest.
Time does most of the work
The page's tables show how strongly time drives the result. At 8%, 40 years of $500 a month puts in twice as much as 20 years, but it ends with more than 5 times the balance: $1,745,504 against $294,510. The early deposits have decades longer to earn interest on their interest.
Doubling time tells the same story. The rule of 72 says money doubles in about 72 divided by the yearly rate, in years. At 8%, that is about 9 years, and at 4%, about 18. The rule is closest near 8% and runs a little long at low rates.
What moves the answer most
The rate matters far more than how often interest compounds. $10,000 at 5% for 10 years grows to $16,289 compounded yearly, $16,470 monthly and $16,487 daily. Daily compounding adds just $198 over the decade. At 6% compounded yearly, the same $10,000 reaches $17,908.
The rate you can earn varies widely. In the FDIC's national rates published September 21, 2026, the average savings account paid 0.37%. A money market account paid 0.63% and a 12-month CD 1.73%. At 0.37%, $10,000 grows to just $10,376 in 10 years, and money takes about 188 years to double.
| Account | Rate | $10,000 after 10 years |
|---|---|---|
| Savings account | 0.37% | $10,376 |
| 12-month CD | 1.73% | $11,871 |
| S&P 500, 1957 to 2026 average | 10.7% | $27,636 |
The S&P 500 returned about 10.7% a year from 1957 to 2026 with dividends reinvested, from Robert Shiller's data. But stock returns swing from year to year and are never guaranteed. The calculator treats any rate as steady, so for investments it shows what an average return over the whole period would produce.
The calculator can also raise what you add each year. At 3%, $500 a month becomes $515 a month in year two. Applied to the opening example, that lifts the 30-year balance to about $914,745, from $295,452 put in.
APY and APR
Compare accounts by APY, the annual percentage yield, which already counts compounding. A 5% rate compounded monthly is a 5.12% APY, and compounded daily it is 5.13%. Banks must advertise savings rates as an APY under Regulation DD. To use an APY in the calculator, enter it as the rate and pick yearly compounding.
Card debt compounds the same way. The page cites the Federal Reserve's average credit card APR of 21.19% for August 2026. Charged daily, that adds up to about 23.6% over a year on a balance left unpaid.
What the calculator leaves out
The page calls itself an educational estimate, not financial advice. Balances are in the dollars of the year you reach them, before taxes and fees. A balance 30 years from now will buy less than the same sum today. Banks can change savings rates, and investments can lose money. For savings measured in today's dollars, the retirement and FIRE calculators work after inflation.
Use it on your own site
The compound interest calculator is free to embed on a blog or site with copy-and-paste code, with no ads or tracking. See how to embed it.
Source: FDIC, National rates and rate caps, published September 21, 2026; SEC, Investor.gov: What is compound interest?; S&P 500 returns since 1957, from Robert Shiller's data; Federal Reserve, G.19 consumer credit, August 2026, released October 7, 2026. Checked October 2026. Figures are educational estimates, not financial advice.