Compound Interest Calculator

🎨 Theme:

Initial Investment ($)

Monthly Contribution ($)

Annual Interest Rate (%)

Number of Years

Compound Frequency

What Is a Compound Interest Calculator?

Compound interest calculation demonstrates how earned returns generate additional returns in subsequent periods. Unlike simple interest, compounding applies growth to both the original principal and previously accumulated earnings, creating exponential expansion over time.

Common Uses

Projecting retirement account balances after decades of consistent contributions
Comparing savings account yields across different compounding frequencies
Illustrating the cost of delaying investment contributions by several years
Evaluating bond fund performance with reinvested dividend distributions
Teaching financial literacy concepts about exponential growth visually

Keyboard Shortcuts

Enter starting principal as your initial lump sum investment
Monthly contributions simulate dollar-cost averaging strategies
Annual percentage rates convert automatically to periodic rates internally
The year-by-year table reveals exactly when your interest exceeds contributions
Switch compounding frequencies to see how daily versus monthly compounding affects outcomes

Pro Tips

Starting ten years earlier typically doubles your final balance due to exponential growth curves
Daily compounding yields marginally more than monthly; the difference becomes significant only at very large balances
The Rule of 72 estimates doubling time: divide 72 by your annual return percentage
Increasing contributions by just 1% annually (escalation) dramatically improves outcomes
Tax-advantaged accounts (IRAs, 401ks) compound more efficiently by deferring liability

Frequently Asked Questions

What distinguishes compound from simple interest?

Simple interest applies only to original principal. Compound interest applies to principal plus all previously earned returns.

How does contribution frequency affect results?

More frequent contributions (monthly versus annually) capture more compounding periods, slightly improving outcomes.

What is the formula behind these projections?

A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) - 1) / (r/n)], where PMT equals periodic contribution.

Can this predict stock market returns?

No. It uses fixed assumed rates. Actual investments fluctuate with market volatility.

Why does the table show interest exceeding contributions eventually?

That crossover point demonstrates the power of compounding — your money starts working harder than your new contributions.

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