Compound Interest Calculator
Project how savings grow with compound interest and monthly contributions. Compare growth rate against high-APR debt to make smarter money decisions.
Compound Interest vs Debt: Making the Right Tradeoff
Compound interest is powerful — Einstein reportedly called it the eighth wonder of the world. But when you're carrying 20%+ credit card debt, the math usually favors paying that down before investing or saving beyond a basic emergency fund.
This calculator projects how your savings grow with regular contributions and compound returns. Use it to understand what your money could become over 5, 10, or 20 years — then compare that growth rate against your highest debt APR.
The rule is simple: if your debt costs more than your savings earn, paying debt is the better 'investment.' Credit card at 24% vs savings at 5%? Every dollar toward the card saves 24 cents per year; every dollar saved earns 5 cents. The gap is enormous.
Once high-APR debt is under control, compound growth becomes your ally. Even modest monthly contributions grow significantly over decades. Pair this calculator with the Savings Calculator for goal-based planning and the Budget Calculator to find contribution room.
How These Calculations Work
Transparent methodology — no black boxes. Here's exactly what happens when you use this calculator.
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Enter starting balance, monthly contribution, annual return rate, and years.
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Interest compounds monthly on the growing balance.
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Contributions are added each month after interest accrual.
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Results show final balance, total contributed, and interest earned.
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Compare your return rate against high-APR debt to prioritize wisely.
Frequently Asked Questions
Each month, interest is applied to your balance (including prior interest), then contributions are added. This compounds growth over time.
If your debt APR exceeds your expected return, paying debt usually wins. Use the Emergency Fund vs Debt calculator for a personalized recommendation.
High-yield savings: 4–5%. Balanced investments: 6–8% long-term average. Use a conservative rate for planning.
Regular contributions accelerate growth significantly — especially early on when compounding has more time to work.
Understanding growth helps you compare the opportunity cost of extra debt payments vs investing or saving.