Compound Interest — Growth Over Time
Calculate your investment's future value with compound interest. Earnings on earnings—the eighth wonder of the world.
Why This Matters for Your Finances
Why: Compound interest accelerates wealth over time. Start early and contribute regularly.
How: FV = P(1+r/n)^(nt) + PMT × [((1+r/n)^(nt)−1)/(r/n)]. Principal + contributions grow with compounding.
- ●Rule of 72: years to double ≈ 72 ÷ rate
- ●Start early—time is the key factor
- ●Monthly compounding yields more than annual
- ●Reinvest dividends for maximum growth
Sample Scenarios
Investment Details
⚠️For educational purposes only — not financial advice. Consult a qualified advisor before making decisions.
💡 Money Facts
Rule of 72
— Doubling
~10yr double
— Typical
Future value
— Formula
Compound freq
— Formula
📋 Key Takeaways
- • Rule of 72: Years to double ≈ 72 ÷ rate (at 7%, double in ~10 years)
- • Start early: Time is the most powerful factor
- • Consistency matters: Regular contributions amplify growth
- • Higher frequency helps: Monthly > annual compounding
- • Reinvest dividends to maximize compounding
💡 Did You Know?
📖 How Compound Interest Works
Compound interest means earning returns on your returns. Each period, you earn interest on the principal plus previously earned interest. Formula: FV = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) / (r/n)] for contributions.
🎯 Expert Tips
Start Early
Even small amounts compound dramatically over decades.
Increase Contributions
Raise savings rate with raises—avoid lifestyle creep.
Maximize Tax-Advantaged
401(k), IRA, HSA grow tax-free or tax-deferred.
Reinvest Dividends
DRIP (dividend reinvestment) accelerates compounding.
⚖️ Rule of 72 (Years to Double)
| Rate | Years to Double |
|---|---|
| 4% | ~18 years |
| 6% | ~12 years |
| 7% | ~10.3 years |
| 8% | ~9 years |
| 10% | ~7.2 years |
❓ Frequently Asked Questions
What is the difference between simple and compound interest?
Simple: interest only on principal. Compound: interest on principal + prior interest. Compound grows faster.
Does compounding frequency matter much?
Yes, but diminishing returns. Monthly vs annual: small difference. Daily vs monthly: minimal.
What is APY vs APR?
APR = stated rate. APY = effective rate after compounding. APY is higher.
How do I maximize compound growth?
Start early, contribute regularly, reinvest dividends, use tax-advantaged accounts.
📊 By the Numbers
📚 Sources
⚠️ Disclaimer: This calculator provides estimates. Actual returns will vary. Past performance does not guarantee future results.