Compound Interest Word Search
Find 10 essential compound interest and time-value-of-money terms. Click any word to learn how the most powerful force in investing actually works.
Investing Term
Find 10 essential compound interest and time-value-of-money terms. Click any word to learn how the most powerful force in investing actually works.
Study these terms before or after solving the puzzle. Each definition includes a real-world US example.
The principal is the original sum of money invested or borrowed, before any interest is added. In compound interest, the principal grows over time as earned interest is added back to it, creating a new, larger base for future interest calculations. This self-reinforcing growth is what makes compound interest so powerful over long periods.
If you invest $10,000 in an S&P 500 index fund, your principal is $10,000. After 10 years at 10% annual return, that principal has grown to over $25,937 — more than 2.5× your original investment, with no additional contributions.
Interest is the cost of borrowing money or the reward for lending it. In investing, it is the return earned on deposited or invested funds. Simple interest is calculated only on the original principal, while compound interest is calculated on the principal plus all previously earned interest — making compound interest grow exponentially over time.
A savings account paying 5% annual interest on $1,000 earns $50 in year one. With compound interest, year two earns interest on $1,050 — not just $1,000 — accelerating growth with every passing year.
The interest rate is the percentage at which interest is charged or earned on a principal amount, usually expressed annually (APR or APY). In compound interest, the rate determines how fast your money grows. Even small differences in rate — say 6% vs 8% — produce dramatically different outcomes over decades due to compounding\
$10,000 invested at 6% for 40 years grows to $102,857. At 8%, it grows to $217,245 — more than double — showing how a 2% rate difference compounds dramatically over long time horizons.
In the context of compound interest, growth refers to the exponential increase in the value of an investment over time. Unlike linear growth (adding a fixed amount each period), compounding produces growth that accelerates — the larger the balance, the more interest earned, which makes the balance grow even faster. Albert Einstein reportedly called it the eighth wonder of the world.
$1,000 invested at 10% annual return doubles to $2,000 in about 7.2 years (the Rule of 72). It doubles again to $4,000 in another 7.2 years — the same time period producing twice the dollar gain, illustrating accelerating growth.
Annual refers to something occurring once per year. In compound interest, the compounding frequency matters enormously. Annual compounding adds interest once a year. Monthly compounding adds it 12 times, quarterly 4 times, daily 365 times. More frequent compounding means slightly faster growth — the difference between nominal and effective annual rate.
$10,000 at 10% compounded annually grows to $11,000 after one year. Compounded monthly, it grows to $11,047 — a small difference in year one that becomes significant over decades.
Return is the gain or loss on an investment over a specified period, expressed as a percentage of the initial cost. In compound interest calculations, the return each period is added to the principal, which then earns returns itself in future periods. Total return includes both price appreciation and any income (dividends or interest) generated by the investment.
The S&P 500 has delivered an average annual total return of approximately 10% over the last 50 years, including dividends. A $10,000 investment made in 1974 would be worth over $1.1 million today, compounded annually at that rate.
Savings are funds set aside from current income rather than consumed. In the context of compound interest, savings are the fuel that starts the compounding engine. The earlier you save, the longer compounding has to work. Even small regular savings contributions, when started early, can grow to substantial sums over decades through the power of compounding.
Saving $200 per month starting at age 25 in an index fund averaging 8% annually results in over $702,000 by age 65. Starting at 35 instead and saving the same amount results in only $298,000 — showing the enormous cost of delayed savings.
Future value is the value of a current asset or investment at a specified date in the future, based on an assumed rate of growth. The compound interest formula calculates future value: FV = PV × (1 + r)^n, where PV is present value, r is the periodic interest rate, and n is the number of periods. Future value is the core concept behind retirement planning.
$5,000 invested today (present value) at 7% annually for 30 years has a future value of $38,061. This single calculation shows why starting a Roth IRA young can lead to tax-free wealth accumulation worth hundreds of thousands.
Doubling time is how long it takes for an investment to double in value at a given compound interest rate. The Rule of 72 provides a quick estimate: divide 72 by the annual interest rate to get the approximate years to double. At 6%, money doubles in 12 years. At 12%, it doubles in 6 years. This rule helps investors intuitively understand the power of different return rates.
Warren Buffett\
Reinvesting means using the returns generated by an investment — dividends, interest, or capital gains — to purchase more of the same investment rather than withdrawing the cash. Reinvestment is the mechanism that makes compound interest work in practice. Without reinvestment, you only earn simple interest on the original principal.
An investor who reinvested all S&P 500 dividends from 2000 to 2020 earned roughly 8.2% annually. An investor who took dividends as cash earned only 5.9% annually. The 2.3% annual difference from reinvestment compounded into a 40% larger portfolio over 20 years.