How much will I have if I invest ¥30,000 a month for 20 years?

The principal is ¥7.2 million. At 3% a year it grows to about ¥9.85 million (gains of about ¥2.65 million), at 5% about ¥12.33 million (gains of about ¥5.13 million), and at 7% about ¥15.63 million. A 2% difference in return changes the amount after 20 years by about ¥2.5 million. The quick-reference table by return on the "Build by saving" tab compares 0 to 10% for the same conditions at once.

What is compound interest, and how is it different from simple interest?

With simple interest, interest is paid only on the original principal. With compound interest, interest is paid on the principal plus the interest earned so far. If you leave ¥1 million at 5% a year for 10 years, simple interest gives ¥1.5 million, while annual compounding gives about ¥1.63 million. The difference is tiny in the first few years, but the longer the period, the more interest earns interest and the wider the gap grows. The chart on the "Lump sum & compound" tab shows the two lines pulling apart.

What is the formula for the savings calculation?

Let P be the monthly contribution, r the monthly rate (annual rate ÷ 12) and n the number of contributions (years × 12). The future amount is P × {(1 + r)^n − 1} ÷ r. For ¥30,000 a month at 3% a year for 20 years, the monthly rate is 0.25% and n is 240, so 30,000 × (1.0025^240 − 1) ÷ 0.0025 ≈ ¥9.849 million. This tool actually accumulates month by month, and the result matches the formula.

How much should I invest each month to reach ¥20 million?

At 5% a year, about ¥49,000 a month over 20 years or about ¥24,000 a month over 30 years. At 3% a year, about ¥61,000 over 20 years or about ¥34,000 over 30 years. Saving without investing would require about ¥83,000 a month for 20 years or about ¥56,000 for 30 years. The "Work back from a goal" tab calculates this for your own conditions, including an initial investment.

How different is the amount I receive in NISA versus a taxable account?

In a taxable account, 20.315% tax is charged on the gains. For ¥30,000 a month at 5% for 20 years, the value is about ¥12.33 million and the gains about ¥5.13 million; in a taxable account about ¥1.04 million of tax is deducted, leaving about ¥11.29 million. With NISA there is no tax and you receive the full ¥12.33 million. The longer the period and the larger the gains, the bigger this difference gets.

What are the New NISA tax-free allowances?

The Tsumitate Investment Frame (つみたて投資枠) is ¥1.2 million a year (¥100,000 a month) and the Growth Investment Frame (成長投資枠) is ¥2.4 million a year, so you can invest up to ¥3.6 million a year in total. The lifetime tax-free holding limit is ¥18 million on a cost basis, of which at most ¥12 million can be used in the Growth Investment Frame. At ¥100,000 a month you reach ¥18 million in 15 years; at ¥50,000 a month, in 30 years.

What happens if I invest ¥100,000 a month for 15 years and use up the New NISA allowance?

The principal is ¥18 million (the full lifetime allowance), and at 5% a year it grows to about ¥26.73 million. The gains of about ¥8.73 million are tax-free, so you avoid about ¥1.77 million of tax compared with the same investment in a taxable account. Even if you stop contributing afterwards, you can keep the money invested tax-free.

What is the Rule of 72?

It is a rule of thumb: "72 ÷ return (%)" gives the approximate number of years for money to double. At 6% a year it is 72 ÷ 6 = 12 years, at 3% it is 24 years, and at 1% it is 72 years. It closely matches the exact figure for annual compounding (11.9 years at 6%). You can also use it the other way round: to double your money in 10 years you need about 7.2% a year.

What return should I assume?

It depends on what you invest in. Many people use about 0.1 to 0.3% for time deposits, around 3% for balanced mutual funds mixing bonds and stocks, 4 to 6% for global stock index funds, and 6 to 8% (the historical average) for US stocks. These are past averages, not guarantees about the future, so it is wise to also run the numbers with a somewhat lower return.

Can I calculate an initial lump-sum investment together with monthly contributions?

Yes. Enter the amount you invest up front in the initial investment field on the "Build by saving" tab; it is invested from month 1 and your monthly contributions are added on top. For example, an initial ¥1 million plus ¥50,000 a month at 5% for 30 years comes to about ¥46.08 million.

How long will ¥20 million last if I withdraw ¥100,000 a month for retirement?

Without any investment returns it runs out in 16 years 8 months (200 months). If you keep it invested at 3% a year while withdrawing, it extends to about 23 years 2 months. If you withdraw ¥150,000 a month, it lasts only about 13 years 7 months even at 3%. On the "Withdraw" tab, enter your assets, monthly withdrawal and return to check.

It is a rule of thumb that if you withdraw 4% of your assets each year, they are unlikely to run out for 30 years. It became known through research based on historical US stock and bond data (such as the Trinity University study). For ¥20 million, that is ¥800,000 a year, or about ¥67,000 a month. It does not account for inflation, exchange rates or Japanese taxes, so use it only as a guide.

Can I use this for iDeCo too?

The future value of the contributions can be calculated in the same way. For example, contributing ¥23,000 a month, the limit for company employees without a corporate pension, at 3% for 25 years gives about ¥10.25 million. However, iDeCo also has the benefit of contributions being income-deductible (lowering income tax and resident tax) and taxes when you receive the money (retirement income deduction, public pension deduction), and these are not included in this tool.

Are fees such as the management fee included in the calculation?

No. A mutual fund's management fee is deducted daily from the fund assets, so entering the expected return minus the fee rate gives a close result. If you expect 5% a year and the fee is 0.1% a year, use 4.9%; for a product with a 1.5% fee, use 3.5%. For ¥30,000 a month over 20 years, 5% versus 3.5% makes a difference of about ¥1.9 million.

Savings & Compound Interest Simulator (New NISA / Monthly Investing Future Value)

Just enter your monthly contribution, expected return and investing period to see how much you will have in the future, split into principal and investment gains. You can also compare the take-home amount in a New NISA (tax-free) account versus a taxable account, and check whether you stay within the ¥3.6 million annual and ¥18 million lifetime allowances. Work backwards to answer "How much per month to reach ¥20 million?", compare compound versus simple interest on a lump sum with the Rule of 72, and see how many years your retirement savings will last when you draw them down, all on one page.

ABOUT

About Savings & Compound Interest Simulator (New NISA / Monthly Investing Future Value)

The Savings & Compound Interest Simulator calculates how much you will have in the future, split into principal and investment gains, just from your monthly contribution, expected return and investing period. It places the amount you receive tax-free under the New NISA next to the amount in a taxable account (20.315% tax on gains), and also checks whether you stay within the ¥3.6 million annual and ¥18 million lifetime tax-free allowances. On the same page you can work backwards from a goal such as "how much per month to save ¥20 million in 20 years", compare compound and simple interest on a lump sum and use the Rule of 72, and test how long retirement savings last when you draw them down monthly. The savings calculation uses the same "monthly rate = annual rate ÷ 12, compounded monthly" as the Financial Services Agency's asset-building simulation: ¥30,000 a month at 3% a year for 20 years grows to about ¥9.85 million.

How to use Savings & Compound Interest Simulator (New NISA / Monthly Investing Future Value)

1On the "Build by saving" tab, enter the monthly contribution, initial investment, expected return and investing period (shorthand such as "3万" for ¥30,000 or "100万" for ¥1,000,000 also works)
2Check the value after the chosen number of years and how much of it is principal and how much is gains
3Compare the amount received under NISA (tax-free) and in a taxable account, and check whether you stay within the New NISA annual and lifetime allowances
4Use the quick-reference table by return to see how much the result changes for each 1% difference in return
5If you have a target amount, use the "Work back from a goal" tab to find the required monthly contribution or the years needed to reach it
6For retirement planning, use the "Withdraw" tab to see how long your assets last given your savings and monthly withdrawal

Great for

Find out how much you would have after investing ¥30,000 a month for 20 years in the New NISA Tsumitate Investment Frame (つみたて投資枠, the allowance for regular fund purchases)
Decide whether to invest ¥10,000, ¥30,000 or ¥50,000 a month by comparing the future amounts
Work backwards to see how much to invest each month, starting now, to build ¥20 million for retirement
Check how much tax you save by investing through NISA instead of a taxable account
Find out how many years it would take to use up the New NISA lifetime allowance of ¥18 million at your current contribution
See how much difference there is after 10 or 20 years between a time deposit and a mutual fund for the same ¥1 million
Use the Rule of 72 to roughly estimate how many years it takes for your assets to double
Check up to what age your assets would last when you draw down your retirement allowance and savings monthly
Get a rough idea of the amount at age 60 if you contribute ¥23,000 a month to iDeCo (individual defined-contribution pension)

Good to know

Contributions are calculated as "saved at the end of each month, with the monthly rate = annual rate ÷ 12 compounded monthly". This is the same assumption as the Financial Services Agency's asset-building simulation, so results are easy to compare with other simulators.
This is an estimate that assumes a constant return every year. Actual returns go up and down from year to year, and some years may show a loss. Even with the same average return, the final amount changes depending on the order of the gains and losses.
The return presets (deposit 0.2%, balanced fund 3%, global stocks 5%, US stocks 7%) are commonly used rules of thumb in simulations. They are not a promise of future performance.
The management fee (expense ratio) of mutual funds is not included. To account for costs, enter the expected return minus the fee rate (for example 5% − 0.1% = 4.9%).
Tax in a taxable account is calculated as 20.315% on the gains when everything is sold at the end (15% income tax, 0.315% special reconstruction income tax and 5% resident tax). Tax on distributions received along the way is not included.
The New NISA allowance is ¥1.2 million a year (¥100,000 a month) for the Tsumitate Investment Frame (つみたて投資枠), ¥2.4 million a year for the Growth Investment Frame (成長投資枠), for a total of ¥3.6 million a year. The lifetime tax-free holding limit is ¥18 million on a cost (purchase price) basis, of which at most ¥12 million can be used in the Growth Investment Frame.
In the New NISA, when you sell, the allowance used by the cost basis of what you sold is restored the following year. This tool assumes you keep investing without selling.
Withdrawals are calculated by repeating "add one month of gains at the start of the month, then withdraw in the same month". Taxes, inflation and pension income are not included.
Everything you enter is calculated in your browser and is never sent to a server.

Questions this tool answers

Use Savings & Compound Interest Simulator (New NISA / Monthly Investing Future Value) for searches like these:

I want to know how much I will have by investing ¥30,000 a month in the new NISA for 20 years
I want to compare the future amount of saving ¥10,000, ¥30,000 or ¥50,000 a month
I want to see the result of maxing out ¥100,000 a month in the Tsumitate Investment Frame
I want to see the principal and gains of regular investing in a chart
I want to work out how much I need per month to save ¥20 million for retirement
I want to know how many years it takes to reach my target amount
I want to compare how much tax differs between NISA and a taxable account
I want to check how many years it takes to use up the New NISA lifetime allowance of ¥18 million
I want to confirm the difference between compound and simple interest in yen
I want to know what ¥1 million becomes after 10 years at 5% a year
I want to know how many years it takes to double my assets with the Rule of 72
I want to see how much difference there is between a 3% and a 5% return
I want to know how long my retirement allowance lasts if I withdraw it monthly
I want to calculate how much I can spend per month under the 4% rule
I want a rough idea of the future amount if I contribute to iDeCo

FAQ

How much will I have if I invest ¥30,000 a month for 20 years?: The principal is ¥7.2 million. At 3% a year it grows to about ¥9.85 million (gains of about ¥2.65 million), at 5% about ¥12.33 million (gains of about ¥5.13 million), and at 7% about ¥15.63 million. A 2% difference in return changes the amount after 20 years by about ¥2.5 million. The quick-reference table by return on the "Build by saving" tab compares 0 to 10% for the same conditions at once.
What is compound interest, and how is it different from simple interest?: With simple interest, interest is paid only on the original principal. With compound interest, interest is paid on the principal plus the interest earned so far. If you leave ¥1 million at 5% a year for 10 years, simple interest gives ¥1.5 million, while annual compounding gives about ¥1.63 million. The difference is tiny in the first few years, but the longer the period, the more interest earns interest and the wider the gap grows. The chart on the "Lump sum & compound" tab shows the two lines pulling apart.
What is the formula for the savings calculation?: Let P be the monthly contribution, r the monthly rate (annual rate ÷ 12) and n the number of contributions (years × 12). The future amount is P × {(1 + r)^n − 1} ÷ r. For ¥30,000 a month at 3% a year for 20 years, the monthly rate is 0.25% and n is 240, so 30,000 × (1.0025^240 − 1) ÷ 0.0025 ≈ ¥9.849 million. This tool actually accumulates month by month, and the result matches the formula.
How much should I invest each month to reach ¥20 million?: At 5% a year, about ¥49,000 a month over 20 years or about ¥24,000 a month over 30 years. At 3% a year, about ¥61,000 over 20 years or about ¥34,000 over 30 years. Saving without investing would require about ¥83,000 a month for 20 years or about ¥56,000 for 30 years. The "Work back from a goal" tab calculates this for your own conditions, including an initial investment.
How different is the amount I receive in NISA versus a taxable account?: In a taxable account, 20.315% tax is charged on the gains. For ¥30,000 a month at 5% for 20 years, the value is about ¥12.33 million and the gains about ¥5.13 million; in a taxable account about ¥1.04 million of tax is deducted, leaving about ¥11.29 million. With NISA there is no tax and you receive the full ¥12.33 million. The longer the period and the larger the gains, the bigger this difference gets.
What are the New NISA tax-free allowances?: The Tsumitate Investment Frame (つみたて投資枠) is ¥1.2 million a year (¥100,000 a month) and the Growth Investment Frame (成長投資枠) is ¥2.4 million a year, so you can invest up to ¥3.6 million a year in total. The lifetime tax-free holding limit is ¥18 million on a cost basis, of which at most ¥12 million can be used in the Growth Investment Frame. At ¥100,000 a month you reach ¥18 million in 15 years; at ¥50,000 a month, in 30 years.
What happens if I invest ¥100,000 a month for 15 years and use up the New NISA allowance?: The principal is ¥18 million (the full lifetime allowance), and at 5% a year it grows to about ¥26.73 million. The gains of about ¥8.73 million are tax-free, so you avoid about ¥1.77 million of tax compared with the same investment in a taxable account. Even if you stop contributing afterwards, you can keep the money invested tax-free.
What is the Rule of 72?: It is a rule of thumb: "72 ÷ return (%)" gives the approximate number of years for money to double. At 6% a year it is 72 ÷ 6 = 12 years, at 3% it is 24 years, and at 1% it is 72 years. It closely matches the exact figure for annual compounding (11.9 years at 6%). You can also use it the other way round: to double your money in 10 years you need about 7.2% a year.
What return should I assume?: It depends on what you invest in. Many people use about 0.1 to 0.3% for time deposits, around 3% for balanced mutual funds mixing bonds and stocks, 4 to 6% for global stock index funds, and 6 to 8% (the historical average) for US stocks. These are past averages, not guarantees about the future, so it is wise to also run the numbers with a somewhat lower return.
Can I calculate an initial lump-sum investment together with monthly contributions?: Yes. Enter the amount you invest up front in the initial investment field on the "Build by saving" tab; it is invested from month 1 and your monthly contributions are added on top. For example, an initial ¥1 million plus ¥50,000 a month at 5% for 30 years comes to about ¥46.08 million.
How long will ¥20 million last if I withdraw ¥100,000 a month for retirement?: Without any investment returns it runs out in 16 years 8 months (200 months). If you keep it invested at 3% a year while withdrawing, it extends to about 23 years 2 months. If you withdraw ¥150,000 a month, it lasts only about 13 years 7 months even at 3%. On the "Withdraw" tab, enter your assets, monthly withdrawal and return to check.
What is the 4% rule?: It is a rule of thumb that if you withdraw 4% of your assets each year, they are unlikely to run out for 30 years. It became known through research based on historical US stock and bond data (such as the Trinity University study). For ¥20 million, that is ¥800,000 a year, or about ¥67,000 a month. It does not account for inflation, exchange rates or Japanese taxes, so use it only as a guide.
Can I use this for iDeCo too?: The future value of the contributions can be calculated in the same way. For example, contributing ¥23,000 a month, the limit for company employees without a corporate pension, at 3% for 25 years gives about ¥10.25 million. However, iDeCo also has the benefit of contributions being income-deductible (lowering income tax and resident tax) and taxes when you receive the money (retirement income deduction, public pension deduction), and these are not included in this tool.
Are fees such as the management fee included in the calculation?: No. A mutual fund's management fee is deducted daily from the fund assets, so entering the expected return minus the fee rate gives a close result. If you expect 5% a year and the fee is 0.1% a year, use 4.9%; for a product with a 1.5% fee, use 3.5%. For ¥30,000 a month over 20 years, 5% versus 3.5% makes a difference of about ¥1.9 million.

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