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Compound Interest Calculator
Calculate the future value of an investment with compound interest and monthly contributions.
Presets:
Your Investment
Settings
Formula
FV = P × (1 + r/n)^(n×t) + PMT × [ (1 + r/n)^(n×t) − 1 ] / (r/n)
P = principal, r = annual rate, n = compounds/year, t = years, PMT = monthly contribution
Results
Future Value
¥9,411,123
Total Contributions
¥7,000,000
Total Interest Earned
¥2,411,123
Your money grew by 1.3x
Yearly Breakdown
| Year | Starting Balance | Contributions | Interest Earned | Ending Balance |
|---|---|---|---|---|
| 1 | 1,000,000 | 600,000 | 65,105 | 1,665,105 |
| 2 | 1,665,105 | 600,000 | 99,133 | 2,364,237 |
| 3 | 2,364,237 | 600,000 | 134,902 | 3,099,139 |
| 4 | 3,099,139 | 600,000 | 172,501 | 3,871,640 |
| 5 | 3,871,640 | 600,000 | 212,023 | 4,683,663 |
| 6 | 4,683,663 | 600,000 | 253,568 | 5,537,231 |
| 7 | 5,537,231 | 600,000 | 297,238 | 6,434,469 |
| 8 | 6,434,469 | 600,000 | 343,142 | 7,377,611 |
| 9 | 7,377,611 | 600,000 | 391,395 | 8,369,006 |
| 10 | 8,369,006 | 600,000 | 442,117 | 9,411,123 |
Balance Growth Chart
Growth Over Time
Year 1Year 10
Savings Goal Hint
To reach ¥9,411,123 at year 10, you need ¥60,607/month at the current rate (starting from ¥0).
Your current monthly contribution is ¥50,000 — consider increasing your monthly contribution.
Scenarios at a Glance
| Monthly Contribution | Future Value | Total Contributions | Total Interest Earned |
|---|---|---|---|
| ¥30,000 | ¥6,305,478 | ¥4,600,000 | ¥1,705,478 |
| ¥40,000 | ¥7,858,301 | ¥5,800,000 | ¥2,058,301 |
| ★ Current | ¥9,411,123 | ¥7,000,000 | ¥2,411,123 |
| ¥60,000 | ¥10,963,946 | ¥8,200,000 | ¥2,763,946 |
| ¥70,000 | ¥12,516,769 | ¥9,400,000 | ¥3,116,769 |
Compares how changing your monthly contribution affects the final outcome. Highlighted row is your current setting.
How It Works
Compound interest is the interest on a loan or deposit calculated based on both the initial principal and the accumulated interest from previous periods. This calculator uses the compound interest formula:
FV = P × (1 + r/n)^(n×t) + PMT × [ (1 + r/n)^(n×t) − 1 ] / (r/n)
- P — Initial principal (one-time investment)
- r — Annual interest rate (as a decimal)
- n — Number of times interest is compounded per year
- t — Number of years the money is invested
- PMT — Monthly contribution amount
Example: If you invest ¥1,000,000 at 5% for 10 years with monthly compounding, your money grows to ¥1,647,009 even without adding a single yen.
This calculator runs entirely in your browser. No data is sent to any server.
Disclaimer
This is for informational and educational purposes only. It does not constitute financial advice.
Compound Interest Calculator: Guide
- Intent
- Calculate compound interest with regular monthly contributions. See how your investment grows over time with a yearly breakdown.
- What it does
- Calculates the future value of an investment using the compound interest formula, supports monthly contributions and multiple compound frequencies.
- Key features
- Monthly contributions, Multiple compound frequencies, Yearly growth breakdown, Interest earned summary
- Privacy
- Everything runs locally in your browser. No data is uploaded.
- Best for
- Understanding how compound interest grows savings over time
- Planning retirement or investment contribution strategies
- Comparing different compound frequencies (monthly vs annually)
- Why this tool
- Clear yearly breakdown showing contributions vs interest earned
- Multiple compound frequency options
- Local-only: sensitive financial data stays on your device
How to use
- 1Enter your initial investment and monthly contribution amounts.
- 2Set the expected annual interest rate and investment period.
- 3Choose how often interest compounds (monthly, quarterly, annually).
- 4Review the yearly breakdown and total interest earned.
Common mistakes
- Using the annual rate where a monthly rate is expected (this tool expects an annual rate).
- Assuming constant returns (actual investments fluctuate).
- Forgetting to account for taxes and fees (this calculator does not include them).
Examples
Monthly savings growth
Initial: ¥500,000
Monthly: ¥50,000
Rate: 5%
Years: 10
Compounds: Monthly
Result: ~¥8.4M total (¥3.4M interest)
Long-term compounding
Initial: ¥1,000,000
Monthly: ¥30,000
Rate: 6%
Years: 20
Result: ~¥16.9M total (¥10.9M interest)
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