Compound Interest Calculator
Use this compound interest calculator with a monthly contribution to see year-by-year growth in a clear balance chart.
Formula & worked example
Formula: Monthly rate = (1 + rate ÷ n)^(n ÷ 12) − 1. Balance = previous balance × (1 + monthly rate) + contribution.
Example: 1,000 at 10% compounded yearly for one year, no contributions: 1,000 × 1.10 = 1,100.
Method & source: Compound-growth formula with periodic contributions (end of month). See how we test our calculators.
Next step: try savings goal or loan repayment.
What Is a Compound Interest Calculator?
Compound interest shows how money grows when interest is earned on both your original deposit and on the interest already added. Over long periods this snowball effect is what makes regular saving and investing so powerful.
This compound interest calculator with a monthly contribution lets you add money every month, choose how often interest compounds, and see the balance year by year.
How Our Compound Interest Calculator Works
Enter your starting amount, monthly contribution, interest rate, time period and compounding frequency.
- Compounding frequency: Annually, semi-annually, quarterly, monthly or daily.
- Monthly contributions: Added at the end of each month.
- Final balance: Total value at the end of the period.
- Split: How much is your own money and how much is interest.
- Year-by-year table and chart: The balance broken down for every year.
Rates are treated as nominal annual rates. Real returns will vary, so use results as an illustration, not a guarantee.
Why Compound Interest Matters
Time is the biggest ingredient in compounding. Starting early can matter more than saving a larger amount later.
- See how monthly contributions build wealth over decades.
- Compare different interest rates and time horizons.
- Understand why starting early beats catching up.
- Plan retirement, education and long-term savings.
- Learn how debt with compound interest grows against you.
A year-by-year chart makes the acceleration of compounding visible in a way a single number cannot.
Worked walkthrough: ten years of saving
Starting with 2,000 and adding 150 every month at 5% a year, compounded monthly, the balance after ten years is about 26,586. Your own money makes up 20,000 of that (2,000 plus 120 payments of 150), so roughly 6,586 is interest. The year-by-year table shows the balance passing 10,000 in about the fourth year, and the interest share grows each year because earlier interest earns interest itself. Doubling the time to twenty years does much more than double the interest – that is compounding at work.
Practical tips for compound interest calculations
- Time matters more than most people expect. Starting five years earlier can beat contributing much more later.
- The rate you enter is a nominal annual rate. Real investment returns vary, so test a low, medium and high scenario.
- Compare compounding frequencies to see the effect: more frequent compounding helps, but the size of the gain is small at typical rates.
- Fees reduce returns. If a fund charges 1% a year, subtract it from the rate you enter for a more realistic view.
- The tool does not adjust for inflation or tax. Treat the final balance as a nominal figure, not future purchasing power.
Frequently Asked Questions (FAQs)
Enter your initial deposit, monthly contribution, annual interest rate and years. Each month the balance grows by the periodic rate and your contribution is added.
It is how often interest is added to the balance. More frequent compounding gives slightly higher growth at the same nominal rate.
Simple interest is only calculated on the original amount. Compound interest is calculated on the original amount plus previously earned interest.
At the end of each month, after that month’s interest has been applied.
No. Investment returns vary and fees or tax may apply. The calculator assumes a constant rate for the entire period.
Estimates only – not financial advice. Results assume a constant interest rate, regular payments and no fees, taxes or inflation unless stated. Real accounts and loans differ, and past or assumed returns are not guaranteed. This tool is not financial or investment advice; check your own account or loan terms and speak to a qualified adviser. See our full disclaimer.