How Small Differences in Return Rate Create Huge Long-Term Gaps

A difference of just a few percentage points in annual return can produce a staggering gap in your assets after 20 years. Here we compare simulation results for investing 3 man-yen per month over 20 years at five different annual rates: 1%, 3%, 5%, 7%, and 10%. The total principal in every case is 720 man-yen (3 man-yen x 12 months x 20 years).

For more context, introductory books on risk and return can help you feel the real impact of return rate differences on your wealth.

Simulation Results by Annual Return Rate

The following results are calculated assuming monthly compounding with end-of-period contributions.

  • 1% annual return: Final amount approximately 797 man-yen (gains approximately 77 man-yen)
  • 3% annual return: Final amount approximately 985 man-yen (gains approximately 265 man-yen)
  • 5% annual return: Final amount approximately 1,233 man-yen (gains approximately 513 man-yen)
  • 7% annual return: Final amount approximately 1,563 man-yen (gains approximately 843 man-yen)
  • 10% annual return: Final amount approximately 2,279 man-yen (gains approximately 1,559 man-yen)

Between 1% and 10%, the same 720 man-yen principal produces a gap of roughly 1,482 man-yen in the final amount. Even comparing 5% and 7% reveals a difference of about 330 man-yen, demonstrating that a mere 2% rate difference carries enormous weight over the long term.

The Relationship Between Return Rate and Risk

Higher returns come with correspondingly higher risk. Here is an overview of typical financial products for each return range.

  • Around 1%: Time deposits, individual government bonds. These offer principal protection and high safety, but may fall below the inflation rate.
  • 3-5%: Balanced mutual funds, bond funds. By combining stocks and bonds, you can target moderate returns while keeping risk in check.
  • 5-7%: Domestic and international stock index funds. Historical data shows global equity indices have averaged roughly 5-7% annual returns.
  • 10% and above: Emerging market stocks, concentrated individual stock portfolios. While high returns are possible, the risk of principal loss is also significant.

Choosing the Right Return Rate for You

The most important factor in choosing a target return rate is accurately understanding your own risk tolerance and investment horizon. If you are in your 20s or 30s with a 20+ year horizon, it is rational to accept short-term volatility and build a portfolio centered on stock index funds targeting 5-7% annual returns. On the other hand, if you are near retirement with a short investment horizon, prioritizing principal safety at 1-3% may be the wiser choice. Try our simulator to check your projected future assets by entering your own contribution amount, time horizon, and expected return rate.

A practical guide to index investing covers the specifics of getting started with low-cost, long-term investing.