Compound Interest Explained
Your money has a rule it follows — whether you know about it or not.
When you put money to work and let the earnings stay invested, those earnings start earning too. Every period, the base gets bigger. And a bigger base means a bigger gain next time.
A = P(1 + r/n)^(nt) The formula that separates people who build wealth from people who wonder where their money went.
under the hood:
Year one, you earn on your original deposit. Year two, you earn on the deposit plus what last year added. The base keeps growing — so the gain keeps growing with it.
Simple interest draws a straight line. Compound interest curves upward. The gap between the two widens every year — quietly at first, then dramatically. The later years do the heavy lifting.
Rate matters. Frequency matters. But time is the biggest factor. Starting 10 years earlier can mean more to your final balance than doubling your rate. Starting now beats waiting for the "right" moment.
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AFinal amount — what your money grows into -
PPrincipal — your starting deposit -
rAnnual interest rate as a decimal (7% = 0.07) -
nNumber of compounding periods per year -
tTime in years
Definitions
Money grows on itself. Each period, the interest you have already earned gets added to your balance. The next round of interest is then calculated on that larger amount — not just your original deposit.
A = P(1 + r/n)^(nt) — where A is your final amount, P is your starting principal, r is the annual rate as a decimal, n is how many times per year it compounds, and t is years invested.
Simple interest is always calculated on the original principal only — growth is a straight line. Compound interest is calculated on a growing base — growth curves upward. Same rate, same time, very different outcome.
Compound interest is the reinvestment of earnings so that returns generate their own returns over time. Warren Buffett called it "the eighth wonder of the world." The mechanism is simple. Most people just start too late to feel it.
The periodic addition of interest to the principal, after which the combined total becomes the new principal for the next compounding period. Common schedules: daily, monthly, quarterly, annually. More frequent compounding means faster growth.
The longer money compounds and the higher the rate, the more dramatic the result. But time matters more than rate. A family that starts at 25 with $5,000 and adds nothing will likely outperform someone who starts at 40 with $50,000 — at the same rate. Start early. Stay consistent.
25+ years of financial planning experience
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Calculator Estimates. The Compound Interest Calculator on this page is a planning tool designed to illustrate how compound interest works over time. All results are hypothetical estimates based on the inputs you provide. They assume a fixed interest rate, consistent compounding, and no withdrawals or additional contributions unless otherwise specified. Actual investment returns vary and are not guaranteed. Past performance does not predict future results. Taxes, fees, and inflation are not reflected in these calculations.
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