Compound Interest Calculator With Monthly Contributions

CalculatorFinance

Compound interest means you earn returns on your earlier returns. Enter a starting amount, an optional monthly deposit, a yearly rate and the number of years to see the future value, how much you put in and how much came from growth.

Quick answer

With compounding, a balance grows as A = P × (1 + r/k)^k×t. 10,000 at 5% a year, compounded monthly for 10 years, grows to about 16,470.09. Regular deposits are added on top using the future-value-of-a-series formula.

Starting amount

Monthly deposit (optional)

Yearly rate (%)

Years

CompoundingMonthlyQuarterlyYearlyDaily

Enter your numbers and press Calculate.

For information only. Results are estimates based on the numbers you enter and are not financial advice. Lenders and banks may round, charge fees or calculate interest differently.

How to use the Compound Interest calculator

1. Enter what you have today (or 0).
2. Enter how much you will add each month, if anything.
3. Enter the expected yearly rate and the number of years, and choose how often interest is compounded.
4. Press Calculate to see the future value and the split between deposits and growth.

The formula

Starting amount: P × (1 + r/k)^(k×t) Monthly deposits (end of month): C × ((1 + i)^m − 1) ÷ i i = (1 + r/k)^(k/12) − 1, m = 12 × t r = yearly rate ÷ 100, k = compounding periods per year

The first line grows the starting balance. The second treats each monthly deposit as a payment made at the end of the month, growing at the monthly rate that matches your chosen compounding.

Worked example

10,000 at 5% compounded monthly for 10 years: (1 + 0.05/12)¹²⁰ ≈ 1.647009, so the balance becomes about 16,470.09. Adding 200 a month on top gives roughly 31,056 more from deposits, for a total near 47,526.

FAQ

What is the difference between simple and compound interest?

Simple interest is paid only on the original amount. Compound interest is also paid on interest already earned, so the balance grows faster over time.

Does compounding frequency matter much?

A little. At 5% a year, monthly compounding gives an effective rate of about 5.116% versus 5% for yearly compounding. The longer the period, the bigger the gap.

Can I use a negative rate?

Yes, a negative rate (above -100%) shows how a balance shrinks, for example to model fees or losses.

Are returns guaranteed?

No. Investment returns vary from year to year. The calculator assumes a steady rate for illustration only.

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