Compound Interest Calculator

See how a lump sum grows with compounding — plus optional regular contributions.

Compound Interest Calculator

See how a lump sum grows with compounding — plus optional regular contributions.

Initial deposit($)

Annual return(%)

Years

Compounding frequency

Additional contribution each month (optional)($)

Enter values above and click Calculate — results will appear here with the formula explained.

FV = P(1 + r/n)^(nt) + C·((1+i)^m − 1)/i where i is the monthly rate and C the monthly contribution

How does this work?

Compound interest pays interest on previously earned interest, so growth accelerates over time. The compounding frequency controls how often earned interest starts earning its own interest — daily beats monthly beats annually, though the difference shrinks at typical rates.

Regular contributions usually matter more than the initial deposit over long horizons. Because each contribution compounds for a different length of time, they're valued with the future-value-of-an-annuity formula and simply added to the lump-sum result.

This projection assumes one steady rate. Markets don't move in straight lines, so treat outputs as planning illustrations rather than promises.

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Disclaimer: Results are estimates for informational purposes only and do not constitute professional financial advice.

Quick Answer

What is the rule of 72? Divide 72 by the annual return to estimate doubling time. At 7%, money doubles roughly every 72/7 ≈ 10.3 years....

Interactive Visualization

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How to Use This Calculator

1Enter your starting balance, expected annual return and time horizon.
2Pick how often returns compound — monthly matches most savings accounts.
3Add a monthly contribution to see how steady saving compounds on top of growth.

Formula Used

FV = P(1 + r/n)^(nt) + C·((1+i)^m − 1)/i where i is the monthly rate and C the monthly contribution

This projection assumes one steady rate. Markets don't move in straight lines, so treat outputs as planning illustrations rather than promises.

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Worked Example

$10,000 at 7% compounded monthly for 10 years grows to about $20,096.61. Adding $250 every month lifts the ending balance to roughly $64,832.29, of which $40,000 came from contributions.

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Compound Interest Calculator vs Top Competitors

Feature	Dream Mining	Investor.gov	NerdWallet	Calculator.net
Free, no signup
Monthly/annual compounding options
Regular contribution support
Inflation-adjusted (real) returns
Interactive growth chart
Rule of 72 / doubling time
Formula & worked example
No ads
FAQ + Speakable schema

Data sourced from competitor websites as of 2026. Features may vary by plan/region. Report correction

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Frequently Asked Questions

QWhat is the rule of 72?

Divide 72 by the annual return to estimate doubling time. At 7%, money doubles roughly every 72/7 ≈ 10.3 years.

QDoes compounding frequency matter much?

At normal rates, modestly. $10,000 at 7% for 10 years yields about $19,671.52 compounded annually versus $20,096.61 monthly — meaningful, but far smaller than the effect of rate or time.

QIs compound interest always good?

It cuts both ways: debt compounds against you. Credit card balances grow by the same mathematics, which is why paying high-APR debt early is powerful.

Formula Used

FV = P(1 + r/n)^(nt) + C·((1+i)^m − 1)/i where i is the monthly rate and C the monthly contribution

This projection assumes one steady rate. Markets don't move in straight lines, so treat outputs as planning illustrations rather than promises.

Feature

Dream Mining

Investor.gov

NerdWallet

Calculator.net

Free, no signup

Monthly/annual compounding options

Regular contribution support

Inflation-adjusted (real) returns

Interactive growth chart

Rule of 72 / doubling time

Formula & worked example

No ads

FAQ + Speakable schema

Frequently Asked Questions

QWhat is the rule of 72?

Divide 72 by the annual return to estimate doubling time. At 7%, money doubles roughly every 72/7 ≈ 10.3 years.

QDoes compounding frequency matter much?

At normal rates, modestly. $10,000 at 7% for 10 years yields about $19,671.52 compounded annually versus $20,096.61 monthly — meaningful, but far smaller than the effect of rate or time.

QIs compound interest always good?

It cuts both ways: debt compounds against you. Credit card balances grow by the same mathematics, which is why paying high-APR debt early is powerful.