Compound Interest Calculator

The SolversPro Compound Interest Calculator is a free financial tool that calculates total accumulated wealth, principal growth, and compound yields over time with custom monthly contributions and compounding frequencies.

See how your money grows over time with the power of compound interest.

Final Amount

Total Invested

Interest Earned

Year-by-Year Growth

Year	Total Invested	Interest Earned	Balance

How It Works

Enter Principal

Enter your starting investment amount.

Add Contributions

Set how much you contribute monthly.

Set Rate

Enter your expected annual return rate.

See Results

View your complete wealth projection.

The Formula

A = P(1 + r/n)^nt + PMT × [((1 + r/n)^nt - 1) / (r/n)]

A = Final amount

P = Principal (starting amount)

r = Annual interest rate (decimal)

n = Compounding frequency per year

t = Number of years

PMT = Monthly contribution

Compounding Frequency & Effective Yield Reference

Comparison of nominal 7% annual interest compounded across different frequencies on a $10,000 principal over 10 years without additional contributions.

Frequency	Periods / Year (n)	Effective Annual Rate (APY)	10-Year Balance	Total Interest
Annually	1	7.000%	$19,671.51	+$9,671.51
Quarterly	4	7.186%	$20,015.97	+$10,015.97
Monthly	12	7.229%	$20,096.61	+$10,096.61
Daily	365	7.250%	$20,136.18	+$10,136.18

Frequently Asked Questions

/What is compound interest?

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which is only calculated on the principal, compound interest grows exponentially over time. This is why Einstein reportedly called it the 'eighth wonder of the world.'

/How is compound interest different from simple interest?

Simple interest is calculated only on the original principal amount. For example, $10,000 at 5% simple interest earns $500 every year. Compound interest is calculated on the principal plus any accumulated interest. So in year two, you'd earn interest on $10,500 instead of $10,000. Over long periods, this difference becomes massive.

/What is the Rule of 72?

The Rule of 72 is a quick way to estimate how long it will take for your investment to double. Simply divide 72 by your annual interest rate. For example, at 8% interest, your money doubles in approximately 72 ÷ 8 = 9 years. At 6%, it takes about 12 years. This rule is most accurate for rates between 6% and 10%.

/Can I really reach $1 million with compound interest?

Yes! With consistent contributions and time, $1 million is very achievable. For example, investing $500 per month at an average 7% annual return would reach $1 million in about 30 years. Starting earlier makes a huge difference — the same $500/month at 7% for 40 years would grow to over $1.3 million.