finance ToolUpdated 2026-09-19
Compound Interest Calculator
Compound interest allows your investments to grow exponentially as your earnings generate their own earnings over time.
Financial & Loan Estimation Notice: Calculations provided are estimates for personal educational planning. Actual loan terms, payment amounts, taxes, and interest charges will vary based on lender underwriting, individual creditworthiness, local statutory regulations, and market conditions.
Formula & Mathematical Methodology
A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) − 1) ÷ (r/n)]
Calculates the future value of initial principal plus the future value of an ordinary annuity stream.
How to Use This Compound Interest Calculator
- Enter starting balance.
- Specify expected return rate.
- Set time horizon.
- Optionally add monthly deposits.
Step-by-Step Worked Example
Scenario: $10,000 initial + $250/month at 7% for 20 years
1. Total principal deposited: $10,000 + ($250 × 240) = $70,000
2. Initial deposit grows to: $40,387.39
3. Monthly deposits grow to: $130,235.25
4. Total future balance: $170,622.64 (Total interest earned: $100,622.64)
Final Calculated Result: $170,622.64
What Does Your Result Mean?
Demonstrates the power of long-term compounding where interest earnings eventually surpass total contributions.
Common Practical Applications:
- Retirement planning (401k, IRA)
- Index fund investing
- College savings funds (529 plans)
Important Limitations & Assumptions:
- Market returns fluctuate and are never guaranteed fixed percentages.
Frequently Asked Questions
What is the Rule of 72?
Divide 72 by your annual interest rate to approximate the number of years required to double your money.
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