Savings & Investment Calculator — Lump Sum + Monthly, Year by Year
Combine an initial lump sum with monthly contributions and see your compound growth broken down year by year — principal vs. investment returns at every step, not just a final number.
| Initial Investment |
JPY
|
|---|---|
| Monthly Contribution |
JPY
|
| Annual Return Rate |
%
|
| Investment Period |
years
|
| Year | Balance | Cumulative Principal | Investment Returns |
|---|---|---|---|
| {{ row.year }} | {{ fmt(row.balance) }} | {{ fmt(row.invested) }} | {{ fmt(row.returns) }} |
Tips
- This calculation includes the compound interest effect. The longer the period, the greater the impact.
- A 5% annual return is a rough historical average for indices like the S&P 500 and global stock index funds. It does not guarantee future results.
- The longer your investment period, the greater the benefit of compounding. Starting early is the single most important factor.
- Using tax-advantaged accounts (such as NISA in Japan, ISA in the UK, or 401(k)/IRA in the US) can make your investment returns and dividends tax-free.
- Even with zero initial investment, regular contributions alone can build significant wealth. A larger initial investment lets you benefit from compounding sooner.
Frequently Asked Questions
Side Note — Why Compound Interest Was Called "the Eighth Wonder of the World"
The quote "compound interest is the greatest invention of mankind" is often attributed to Einstein, though its true origin is uncertain. Regardless, it is cited worldwide as a concise expression of the extraordinary power of compounding.
Investing $300 per month at a 5% annual return for 20 years turns a $72,000 principal into approximately $123,000. Over 30 years, it grows to roughly $250,000 — with investment returns adding more than $120,000 on top.
Compound interest works against you just as powerfully with high-interest debt. Revolving credit at high rates means you are continuously paying compound interest as a borrower. In wealth building, make compounding work for you.