Compound Interest Calculator with Monthly Contributions
See exactly how your money grows over time with daily, monthly, quarterly, or yearly compounding. Add regular contributions and get an AI explanation of your result.
Country
Currency
📈
Calculate Compound Growth
Starting Investment
€
The amount you are starting with today
%
Global average long-term stock market return is approximately 7% per year
yrs
Compounding and Contributions
⟳
€
Regular amount added each month on top of your initial investment
Final Balance
—
after 20 years
Total Interest Earned
—
pure growth
Total Contributed
—
principal + deposits
Year-by-Year Growth
Year
Balance
Interest
Contributed
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💡 Compounding Tips
Starting earlier matters more than investing more. An extra 5 years of compounding can double your final balance.
Daily compounding produces more than monthly, which produces more than annual. The difference grows over long periods.
Compound interest means earning interest on your interest. When you invest money, you earn a return on your principal. Then in the next period, you earn a return on both your original principal and the interest you already earned. Over time this creates exponential growth rather than linear growth.
The Formula
A = P × (1 + r/n)^(n×t)
With regular contributions:
A = P × (1 + r/n)^(n×t) + C × [((1 + r/n)^(n×t) - 1) / (r/n)]
A = final amount. P = principal. r = annual rate as decimal. n = compounding periods per year. t = years. C = monthly contribution.
The Power of Regular Contributions
A one-time investment of 10,000 at 7% for 20 years grows to approximately 40,000. The same 10,000 with an additional 200 per month grows to approximately 104,000. The monthly contributions more than double the final result.
Compound Interest Growth Examples
Starting principal of 10,000, monthly compounding, no additional contributions.
Years
At 4%
At 7%
At 10%
Interest at 7%
5 years
12,190
14,150
16,450
4,150
10 years
14,860
20,020
27,050
10,020
20 years
22,080
40,080
73,220
30,080
30 years
32,810
80,500
198,370
70,500
40 years
48,760
161,700
537,000
151,700
Frequently Asked Questions
What is the difference between compound and simple interest?+
Simple interest is calculated only on your original principal. Compound interest is calculated on your principal plus all previously earned interest. At 7% over 20 years, compound interest produces far more than simple interest on the same investment.
How does compounding frequency affect returns?+
More frequent compounding means interest is added to your balance more often, so you earn interest on a slightly larger amount each time. Daily compounding produces more than monthly, which produces more than annual. Over very long periods the difference becomes noticeable.
What rate should I use for long-term investing?+
For long-term stock market projections, 7% per year is a commonly used conservative assumption. For savings accounts you may use a lower rate, often around 2% to 4% depending on the country and institution.
Does this calculator include tax?+
No. This calculator shows gross growth before tax. If you want an after-tax projection, reduce the interest rate input by your effective tax drag or model the tax separately.
What is the rule of 72?+
Divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 6% it takes around 12 years. At 8% it takes around 9 years.
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