Compound Interest Calculator
Determine how your savings, stocks, or retirement funds grow over time. Features annual, semi-annual, quarterly, monthly, or daily compounding intervals with year-by-year balance projections.
What is the Compound Interest Calculator?
This tool models compound interest growth over time with customizable compounding frequencies, recurring monthly contributions, and inflation adjustments.
The Mathematics of Exponential Growth
Simple interest only pays on the original principal. Compound interest pays interest on previously earned interest, creating an exponential curve. As time progresses, the compounding frequency $n$ (daily, monthly, annually) increases the effective annual yield ($APY = (1 + r/n)^n - 1$). Over multi-decade horizons, reinvested earnings dwarf the original capital contributions.
How to Use the Compound Interest Calculator
Enter Initial Deposit
Type your starting investment amount (e.g. $5,000).
Set Expected Return & Tenure
Enter your anticipated annual interest rate (e.g. 7% to 10% for index funds) and timeframe in years.
Add Monthly Contributions
Input how much you plan to add each month to see recurring deposits accelerate growth.
Inspect Year-by-Year Schedule
Review the breakdown showing when earned interest begins to outpace your personal contributions.
Key Settings & Parameters
| Setting | What It Controls | Recommended Default |
|---|---|---|
| Compounding Frequency | How often interest is calculated and added to the balance. Common options are Annually, Quarterly, Monthly, or Daily. | Monthly for investment accounts and recurring deposits |
| Inflation Adjustment | Discounts the final nominal balance by an assumed inflation rate (e.g. 2.5%) to show real purchasing power in today’s dollars. | 2.5% to 3.0% for long-term horizons |
Common Pitfalls to Avoid
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• Assuming constant returns without volatilityStock market returns fluctuate. An average 9% return includes years with +20% and years with -15%.
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• Ignoring inflation over 20+ year horizonsAlways review purchasing power estimates so you know what $1,000,000 in 30 years will actually buy.
Pro Tips for Best Results
- Starting 5 years earlier can double your retirement nest egg even if you invest less total money, due to compounding runway.
Local Processing Guarantee
Zero server communication. Your financial numbers, balances, and savings plans remain entirely private on your device.
When to Use
- Planning retirement accounts (401k, IRA, Roth IRA, Superannuation).
- Modeling college savings funds, emergency buffers, and index fund portfolios.
- Comparing bank Certificate of Deposit (CD) and High Yield Savings Account (HYSA) yields.
- • Assumes a constant annualized return rate and does not model sequence-of-returns risk or dynamic tax drag.