Compound Interest & Inflation Calculator

Question 1

What is compound interest and how is it different from simple interest?

Answer

Compound interest earns interest on both the original principal and the accumulated interest from all previous periods. Simple interest only earns on the original principal. For example, $10,000 at 7% simple interest grows by $700/year forever. With compound interest, the second year earns on $10,700, the third on $11,449, and so on — growing exponentially. The formula is A = P(1 + r/n)^(nt).

Question 2

How does inflation reduce compound interest returns?

Answer

Inflation silently erodes purchasing power. Even if your investment grows 7% nominally, 3% inflation means prices also rose — your real gain is only ~3.88% (via the Fisher equation). Over 20 years at those rates, $10,000 nominal grows to ~$38,697 but its real value is only ~$21,427. The gap between those two numbers — $17,270 — is the inflation erosion shown in this calculator.

Question 3

What is the Rule of 72 in compound interest?

Answer

The Rule of 72 is a shortcut to estimate doubling time: years to double ≈ 72 ÷ annual rate. At 8%, money doubles in ~9 years. At 4%, ~18 years. It also works for inflation: at 3% inflation, purchasing power halves in ~24 years. This calculator displays the Rule of 72 live as you adjust the interest rate slider.

Question 4

How often should interest compound for best results?

Answer

More frequent compounding always yields slightly more. Daily compounding beats monthly, which beats quarterly, which beats annually. However, the difference is smaller than most expect. At 7% over 20 years on $10,000: annual compounding gives $38,697; daily gives $40,138 — a difference of only ~$1,441. Monthly compounding ($39,983) captures most of the daily benefit and is the most common in real-world savings accounts and mortgages.

Question 5

What is a good real rate of return on investments?

Answer

Historically: the S&P 500 has returned ~10% nominal / ~7% real. Government bonds: ~2–4% nominal / ~1–2% real. Savings accounts: currently 4–5% nominal in high-rate environments. Any real rate above 0% means your wealth is growing in purchasing-power terms. Target at least 3–5% real return to meaningfully build wealth over time.

Question 6

How does monthly contribution affect compound interest growth?

Answer

Regular monthly contributions dramatically accelerate growth through dollar-cost averaging and compounding. The future value of periodic contributions follows the annuity formula: FV = PMT × [(1 + r/n)^(nt) − 1] / (r/n). For instance, adding just $200/month to a $10,000 principal at 7% over 20 years increases the final balance from ~$39,000 to ~$142,000 — nearly 4× more. Start contributions early; even small amounts compound significantly over decades.

Compound Interest & Inflation Calculator

Calculator Parameters

Growth Over Time

Year-by-Year Breakdown

How the Compound Interest & Inflation Calculator Works

Compound Interest Formula

Inflation Adjustment

Fisher Equation

Live Inflation Data

Rule of 72

40+ Currencies

Frequently Asked Questions about Compound Interest