Starlight Tools/Compound Interest Calculator

Compound Interest Calculator

See your money grow over 1 to 30+ years with live charts

Starting amount

$

Monthly contribution

$

Annual return

%

Time horizon

Compounds

In 10 years, you could have

you invest interest earns1.7× your money

Growth over time

what you put in interest earned
$0$20k$40k$60k$14k$18k$33k

hover the chart to inspect any year ✦

Year-by-year breakdown
YearPut inInterestBalance
1$13,000+$942$13,942
2$16,000+$2,212$18,212
3$19,000+$3,836$22,836
4$22,000+$5,844$27,844
5$25,000+$8,268$33,268
6$28,000+$11,141$39,141
7$31,000+$14,503$45,503
8$34,000+$18,392$52,392
9$37,000+$22,853$59,853
10$40,000+$27,933$67,933

“Compound interest is the eighth wonder of the world.”

— attributed to Albert Einstein ✦

For learning and planning only. Markets go up and down, this projection assumes a steady return and is not financial advice.

FAQ

How is compound interest calculated?

The classic formula is A = P(1 + r/n)^(nt), where P is your starting amount, r the yearly rate, n how often it compounds, and t the years. This calculator also adds your monthly contributions each step, which is how most people actually invest.

Did Einstein really call compound interest the eighth wonder of the world?

The quote is widely attributed to Einstein, though historians have never found a solid source. True or not, the math behind it is real: growth on top of growth snowballs dramatically over decades.

Why do monthly contributions matter so much?

Every contribution starts earning its own interest immediately. Over 20 or 30 years, steady monthly deposits often end up producing more of the final balance than the starting lump sum.

What return rate should I use?

That depends on what you are modeling. Long-run broad stock market averages are often quoted around 7 to 10% before inflation, while savings accounts are far lower. This tool is for education, not financial advice, so try a few scenarios.