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§ Finance·High school

Compound Interest Worksheets

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Easy

10 problems

Medium

20 problems

Hard

20 problems

Mixed

30 problems

Free printable compound interest worksheets with step-by-step answer keys. Every worksheet is uniquely generated so students never see the same problems twice. Topics covered range from single-year interest on a savings account at the easy level through to future value with monthly contributions (annuity) at the advanced level.

LK20.10.financeCCSS.HSF.IF.C.8bNC.KS4.RP

What is compound interest?

Compound interest occurs when interest earned on an initial investment or deposit begins earning interest itself, creating exponential growth rather than linear growth. The formula A = P(1 + r)n calculates the final amount, where P represents principal, r the annual interest rate as a decimal, and n the number of years. This mathematical concept forms the foundation of long-term wealth building and appears in savings accounts, investment funds, and retirement planning.

Why it matters

Compound interest drives the mathematics behind retirement savings, college funds, and long-term investments. A person who invests $5,000 annually starting at age 25 will accumulate approximately $1,142,000 by age 65 at a 7% return, while someone starting at age 35 with the same contributions reaches only $540,000. This $602,000 difference illustrates why financial advisors emphasize early investing. The concept appears in mortgage calculations, where borrowers pay compound interest to lenders, and in credit card debt, where unpaid balances compound monthly. Index funds rely on compound growth to build wealth over decades, turning modest monthly contributions into substantial retirement accounts through the mathematical power of exponential growth.

Common mistakes to watch for

  • ✗Confusing simple and compound interest calculations — computing $1,000 at 5% for 3 years as $1,150 (simple interest) instead of $1,157.63 (compound interest).
  • ✗Forgetting to convert percentage rates to decimals — using 0.05^3 instead of (1.05)^3 when calculating compound growth.
  • ✗Mixing up principal and final amount in the formula — writing P = A(1 + r)^n instead of A = P(1 + r)^n.

Questions teachers ask

What is the difference between simple and compound interest?+
Simple interest calculates earnings only on the original principal, while compound interest calculates earnings on both principal and previously earned interest. For $1,000 at 5% over 10 years, simple interest yields $1,500 while compound interest yields $1,628.89.
How often does compound interest typically compound?+
Savings accounts usually compound daily or monthly, while investment accounts compound annually when dividends reinvest. Monthly compounding uses the formula A = P(1 + r/12)^(12n), where the rate divides by 12 and time multiplies by 12.
Why does compound interest create exponential growth?+
Each period's interest becomes part of the principal for the next period, creating a multiplicative effect rather than additive. The mathematical function (1 + r)^n represents exponential growth, where small rates over long periods produce dramatic increases.
How do you calculate compound interest with monthly contributions?+
Use the future value of annuity formula: FV = PMT × [((1 + i)^n - 1) / i], where PMT is the monthly payment, i equals the annual rate divided by 12, and n represents total months.
What interest rate should you use for long-term calculations?+
Historical stock market returns average 7-10% annually, while savings accounts offer 1-5%. Conservative estimates use 6-7% for diversified investments, though actual returns vary significantly year to year and past performance doesn't guarantee future results.
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Beginner

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Concepts
Single-year interest on a savings account
Range
principal: 1000–10000, rate: 2–6%
Steps
2 steps
Example
5000 at 4% for 1 year

Easy

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Concepts
Compound interest over 2–3 years (annual)
Range
principal: 5000–20000, rate: 3–6%, years: 2–3
Steps
3–4 steps
Example
10000 at 5% compounded annually for 3 years

Medium

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Concepts
Index fund / mutual fund growth over 5–15 years
Range
principal: 10000–50000, rate: 5–8%, years: 5–15
Steps
3 steps
Example
20000 invested in an index fund at 7% for 10 years

Hard

Generate →
Concepts
Future value with monthly contributions (annuity)
Range
PMT: 500–2000, rate: 4–8%, years: 10–30
Steps
4 steps
Example
Save 1000/month at 6% for 20 years

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