Compound Interest Calculator

Calculate compound interest growth free online using the standard compounding formula. See your investment's future value with monthly, quarterly, or annual compounding.

Principal

Annual Rate (%)

Years

Compounding

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How to Use This Tool

Enter principal and rateYour starting amount and annual interest rate

Set years and compounding frequencyHow long it grows and how often interest compounds

See future value and total interestCalculated with the standard compound interest formula

Interest That Earns Interest -- Why Time Matters Most

Compound interest grows exponentially rather than linearly because each compounding period calculates interest on an increasingly larger base -- the original principal plus all previously earned interest. This is why financial advice consistently emphasizes starting early: a longer time horizon matters more than a larger initial amount for long-term compound growth.

Compounding Frequency's Modest But Real Effect

Monthly compounding produces a slightly higher final amount than annual compounding at the identical nominal rate, since interest gets folded into the principal more often. The difference is usually modest at typical rates but becomes more noticeable at higher rates or over longer time horizons.

Lump Sum Versus Regular Contributions

This calculator models a single lump sum growing over time. Real investing often involves regular contributions added on top of an initial sum, which uses a different annuity-style formula and produces meaningfully different (typically larger) results than lump-sum growth alone -- worth keeping in mind if your actual situation includes ongoing contributions.

Frequently Asked Questions

A = P(1 + r/n)^(nt), where P is principal, r is annual rate, n is compounding frequency per year, and t is years. This is the standard formula used universally for compound growth calculations.

More frequent compounding (monthly vs annual) means interest gets added to the principal more often, so subsequent interest calculations work off a slightly larger base each time -- producing a modestly higher final amount than less frequent compounding at the identical nominal rate.

Simple interest calculates only on the original principal throughout the term. Compound interest calculates on principal plus previously earned interest, which is why compound growth accelerates over time -- it's interest earning interest.

This calculator computes growth on a single lump sum. Adding regular contributions on top requires a different formula (annuity-style compounding), which produces a different and typically larger total than lump-sum growth alone.

Because the growth curve is exponential, not linear -- the longer the time horizon, the more dramatic the difference between compound and simple growth becomes, which is why starting early matters more than the specific amount for long-term wealth building.