See how a lump sum grows over time with compound interest, with optional monthly contributions added in.
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Projected Balance
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Total Contributions—
Total Interest Earned—
Formula
Balance grows each year as Balance × (1 + rate) plus that year of contributions, compounding annually.
Example
Starting with $10,000 and adding $200/month at 7% annual growth for 20 years grows to roughly $124,000, more than half of it from compound interest.
Not tax or financial advice. This calculator provides general estimates based on published 2026 figures. Always confirm important figures with the IRS, SSA, your state tax agency, a licensed lender, or a qualified professional.
Frequently Asked Questions
What does compounding mean?
Compounding means interest earned in one period is added to the balance, so future interest is earned on the original amount plus all prior interest.
Does contribution timing matter?
This calculator applies contributions once per year for simplicity. Contributing more frequently, such as monthly, produces slightly higher growth in reality.