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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

YearStarting BalanceContributionsInterest EarnedEnding Balance
11,000,000600,00065,1051,665,105
21,665,105600,00099,1332,364,237
32,364,237600,000134,9023,099,139
43,099,139600,000172,5013,871,640
53,871,640600,000212,0234,683,663
64,683,663600,000253,5685,537,231
75,537,231600,000297,2386,434,469
86,434,469600,000343,1427,377,611
97,377,611600,000391,3958,369,006
108,369,006600,000442,1179,411,123
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.

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

  1. 1Enter your initial investment and monthly contribution amounts.
  2. 2Set the expected annual interest rate and investment period.
  3. 3Choose how often interest compounds (monthly, quarterly, annually).
  4. 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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