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💰 Compound Interest Calculator

Calculate investment growth with compound interest over time

Finance Calculator

Compound interest — Quick answer

Compound interest earns interest on previously accumulated interest. The future value depends on principal, rate, time, and compounding frequency.

FV = P × (1 + r/n)n·t
With monthly contributions: FV = P·(1+r/n)nt + PMT·((1+r/n)nt−1)/(r/n)

Worked example: $1,000 principal at 5% APR compounded monthly for 10 years. FV = 1,000 × (1 + 0.05/12)120 = 1,000 × 1.6470 = $1,647.01. Add $100/month: FV = 1,647 + 100 × ((1.00417120−1)/0.00417) = $17,176.

$1,000 invested for 30 years at varying rates (monthly compounding)

Rate10 years20 years30 years
3%$1,348$1,820$2,457
5%$1,647$2,712$4,468
7%$2,010$4,038$8,116
10%$2,707$7,328$19,837
12%$3,300$10,893$35,950

Standard / source: Standard financial mathematics; SEC requires APR disclosure on loans (Truth in Lending Act).

Used for: Retirement planning, savings goal setting, mortgage interest projection, education-fund planning, FIRE-movement calculations.

💰 Compound Interest Calculator

Formula

This calculator uses the standard compound interest calculator formula:

Compound Interest Formula
A = P × (1 + r/n)^(n×t)

Frequently Asked Questions

What is compound interest? ⌄

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. It grows faster than simple interest over time.

What is the compound interest formula? ⌄

A = P × (1 + r/n)^(n×t), where P = principal, r = annual rate (decimal), n = compounds per year, t = years.

How much does $10,000 grow at 7% for 10 years? ⌄

Using annual compounding: A = 10,000 × (1.07)^10 = $19,671.51. Total interest earned = $9,671.51.

What is the Rule of 72? ⌄

The Rule of 72 estimates how long it takes to double an investment: divide 72 by the annual interest rate. At 8%, money doubles in approximately 9 years.

How does compounding frequency affect growth? ⌄

More frequent compounding means slightly higher returns. Monthly compounding yields more than annual compounding at the same stated interest rate.

What is the difference between APR and APY? ⌄

APR (Annual Percentage Rate) is the stated rate without compounding. APY (Annual Percentage Yield) includes the effect of compounding and reflects actual annual return.

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Standards & method

✓ Independently verified 12 July 2026
Basis
First principles
Method
Compound interest. No standard governs it; APR/APY disclosure is regulated (TILA/Reg Z in the US).
Core formula
A = P(1 + r/n)^(nt)
Why this matters
Compounding frequency changes the outcome — the same nominal rate compounded daily beats annually. And a nominal return below inflation is a real LOSS, however positive the number looks. Figures are illustrative, not financial advice.
Independently verified
12 July 2026 — Formula re-derived from first principles and verified numerically against hand-computed reference cases, including edge cases and unit handling.

Results are for guidance. Verify against the current edition of the governing standard and have a qualified professional review before use in practice.