复利计算器
计算复利和投资增长。
本金设置
增长轨迹
最终余额
$838,978
总投入
$250,000
利息收益
$588,978
PNG 高分辨率 | 100% 客户端
The Power of Compound Interest
Overview
Compound interest is interest earned on both your original principal and on previously-accumulated interest. Albert Einstein reputedly called it 'the most powerful force in the universe' — though that quote is apocryphal, the underlying math is real. A modest 7% annual return doubles your money every 10 years through compounding. Over 40 years of working life, a single $10,000 investment becomes about $150,000 without adding another dollar. Understanding this changes how you think about retirement savings, debt, and time itself.
How It Works
The formula is A = P(1 + r/n)^(nt), where A is the final amount, P is principal, r is annual interest rate, n is compounding periods per year, and t is years. With monthly compounding (n=12), a 5% annual rate effectively becomes ~5.116% (the 'APY' or annual percentage yield). The calculator handles all combinations — you input the principal, optional regular contributions, rate, time, and compounding frequency, and it shows both the final balance and a year-by-year breakdown.
When to Use This
Run this when planning retirement contributions to see how starting earlier dramatically changes outcomes. Compare loan offers by computing total interest paid (compound interest works against you on debt). Evaluate whether to invest in index funds vs paying off low-interest debt. Show kids and teens what saving $50/month from age 18 turns into by age 65 — the result is shocking enough to motivate lifetime saving habits.
Frequently Asked Questions
What's the difference between simple and compound interest?
Simple interest accrues only on the original principal. Compound interest accrues on principal + accumulated interest, so it grows exponentially. Over 30 years at 7%, $10,000 becomes $31,000 with simple interest, but $76,000 with annual compounding.
Why does compounding frequency matter?
More frequent compounding (daily vs annually) slightly increases your final balance, but the effect plateaus quickly. The difference between monthly and daily compounding over 30 years is usually less than 1%. Annual rate matters far more than frequency.
How realistic is 7% return?
The S&P 500's long-term average is ~10% nominal, ~7% after inflation. But individual years vary wildly (-30% to +30%). Use 5–7% for conservative planning; 7–8% for aggressive but historically-supported estimates.
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