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Compound Interest Calculator

See how an investment grows over time with compound interest. Add optional monthly contributions to model regular savings. Results include a year-by-year breakdown and visual chart.

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Returns are not guaranteed. Past performance does not indicate future results. For Singapore CPF and investment planning, visit AsiaCalc.com.

How to Use the Compound Interest Calculator

1
Enter your principal. This is the starting amount you invest or deposit.
2
Set the interest rate and time period. Use the slider or type the number of years. Add a monthly contribution to model regular savings like a pension or SRS contribution.
3
See the full picture. The bar chart shows how your balance is split between principal and interest each year. The table shows exact figures for every year.

Compound Interest Formula

Without contributions:

A = P x (1 + r/n)^(n x t)

With monthly contributions (PMT):

A = P x (1 + r/n)^(nt) + PMT x (12/n) x ((1 + r/n)^(nt) - 1) / (r/n)

Where P = principal, r = annual rate as decimal, n = compounding periods/year, t = years, PMT = monthly contribution. This calculator uses a period-by-period simulation for accuracy with all compounding frequencies.

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Frequently Asked Questions

What is compound interest?

Compound interest is interest calculated on both your original principal and the interest you have already earned. Unlike simple interest (which only earns on the original amount), compound interest accelerates growth over time because each period's interest is added to the base for the next calculation.

How is compound interest calculated?

The formula is A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate as a decimal (e.g., 7% = 0.07), n is the number of compounding periods per year, and t is the number of years.

What is better: monthly or annual compounding?

More frequent compounding is better for investors. Monthly compounding gives slightly better returns than quarterly, and daily gives the most. The difference is small but grows over long periods. Most savings accounts and fixed deposits compound monthly or daily.

How long to double money at a given interest rate?

Use the Rule of 72: divide 72 by the annual rate. At 6%, your money doubles in about 12 years (72/6). At 8%, about 9 years. At 10%, about 7.2 years. This calculator shows your exact balance at any year using the precise formula.

What is the compound interest formula?

A = P(1 + r/n)^(nt) for a lump sum with no contributions. For regular contributions, the formula adds the future value of an annuity: PMT x ((1 + r/n)^(nt) - 1) / (r/n). See the formula box above for the full version including monthly contributions.