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. Consult a qualified professional for decisions.

What is Compound Interest?

Quick Answer

Compound Interest Calculator computes see how a lump sum grows with compounding — plus optional regular contributions. Formula: FV = P(1 + r/n)^(nt) + C·((1+i)^m − 1)/i where i is the monthly rate and C the monthly contribution. Example: $10,000 at 7%.

What it does: See how a lump sum grows with compounding — plus optional regular contributions.
Formula: FV = P(1 + r/n)^(nt) + C·((1+i)^m − 1)/i where i is the monthly rate and C the monthly contribution
Inputs: Initial deposit ($) · Annual return (%) · Years · Compounding frequency · Additional contribution each month (optional) ($)
Example: $10,000 at 7% compounded monthly for 10 years grows to about $20,096.

Calculator Inputs at a Glance

Field	What to enter
Initial deposit ($)	e.g. 10000
Annual return (%)	e.g. 7
Years	e.g. 10
Compounding frequency	Enter a value
Additional contribution each month (optional) ($)	e.g. 250

All fields use the exact formulas shown below — results include step-by-step breakdowns you can verify by hand.

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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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.

What is Compound Interest?

Quick Answer

What it does: See how a lump sum grows with compounding — plus optional regular contributions.

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

Inputs: Initial deposit ($) · Annual return (%) · Years · Compounding frequency · Additional contribution each month (optional) ($)

Example: $10,000 at 7% compounded monthly for 10 years grows to about $20,096.

Field

What to enter

Initial deposit ($)

e.g. 10000

Annual return (%)

e.g. 7

Years

e.g. 10

Compounding frequency

Enter a value

Additional contribution each month (optional) ($)

e.g. 250

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.

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.