What is the compound interest formula?

A common form is A = P(1 + r/n)^(n·t), where P is principal, r the annual rate as a decimal, n the number of compounding periods per year, and t the time in years. Contributions are added on top of that base model.

Does monthly compounding grow faster than annual?

Yes, all else equal: interest is credited more often, so later periods earn on a larger balance. The difference is modest at low rates and short horizons, and larger over decades.

Are these results guaranteed returns?

No. Markets, fees, taxes, and product terms change real outcomes. Treat the number as a planning estimate only.

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Compound interest

Estimate how savings or investments grow when interest is added to the balance and then earns interest itself. Adjust principal, rate, time, and optional contributions.

Initial capital

Monthly contribution

Estimated annual rate

Term

years

Final capital

$ 113,669.42

Contributions at the end of each month.

Contributed

$ 70,000

Interest

$ 43,669.42

38.4 % of final capital.

This is a mathematical projection, not a return guarantee. The rate is assumed constant with monthly compounding.

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About this calculator

Compound interest is the process of earning returns on both the original principal and on interest already credited. Over long periods, small differences in rate or contribution frequency can change the final balance substantially.

This calculator projects a future value from the starting amount, an annual percentage rate, the number of years, how often interest is applied, and optional recurring deposits. All math runs in your browser; nothing is stored on a server.

Use it to compare save monthly vs yearly, to see the impact of a higher rate, or to stress-test a goal before you commit to a product. Results are mathematical estimates—not advice and not a guarantee of any bank or fund return.

How to use it

1Enter the starting principal (what you invest or save today).
2Set the annual interest rate and how many years you will leave the money invested.
3Choose compounding frequency and, if you want, a regular contribution amount.
4Review the projected balance and compare with a second scenario if needed.

Frequently asked questions

What is the compound interest formula?: A common form is A = P(1 + r/n)^(n·t), where P is principal, r the annual rate as a decimal, n the number of compounding periods per year, and t the time in years. Contributions are added on top of that base model.
Does monthly compounding grow faster than annual?: Yes, all else equal: interest is credited more often, so later periods earn on a larger balance. The difference is modest at low rates and short horizons, and larger over decades.
Are these results guaranteed returns?: No. Markets, fees, taxes, and product terms change real outcomes. Treat the number as a planning estimate only.

Results are mathematical estimates. Verify the real conditions of any financial product before making decisions.