Compound Interest Calculator
See how your money can grow over time. Enter your starting amount, monthly contributions, and expected return rate.
Results
Final Balance
Total Contributions
Total Interest Earned
Year-by-Year Breakdown
| Year | Contributions | Interest | Balance |
|---|---|---|---|
What is compound interest?
Compound interest is when you earn interest not just on your original investment, but also on the interest you've already earned. It's often called "interest on interest" and is one of the most powerful forces in personal finance.
The key to compound interest is time. The longer your money compounds, the faster it grows. Even small monthly contributions can turn into significant wealth over decades. This is why starting early, even with small amounts, matters so much.
Use the calculator above to see how different contribution amounts and time periods affect your final balance. Try adjusting the monthly contribution to see the dramatic difference even $50 more per month can make.
What is compound interest?
Compound interest is the process of earning interest on both your original investment and the interest that has already accumulated. Unlike simple interest — which only applies to the principal — compound interest accelerates growth over time, often called the "eighth wonder of the world."
The longer your money compounds, the more dramatically it grows. A $10,000 investment at 7% annual return with $300 monthly contributions reaches approximately $150,000 after 15 years — over $96,000 of which is pure growth.
How to use this calculator
- 1. Enter your starting amount — what you have saved or plan to invest today.
- 2. Set your monthly contribution — even $100/month makes a significant difference over time.
- 3. Adjust the annual return rate — 6–8% is a common assumption for diversified long-term investing.
- 4. Choose your time horizon — the longer you invest, the more powerful compounding becomes.
Once you know what you can realistically save each month, try the envelope budget planner to find the room in your budget.
Put your plan into action
Start budgeting with Hearth and watch your savings grow.