Japan Small Business Mutual Aid Simulator
Compare Japan’s tax deductions, benefits and member-loan interest.
IS
定投模拟器
含2026年12月iDeCo上限的定投模拟。
Assets after 20 years
Projected after-tax value
¥12.17M
¥12,174,135
Projected assetsContributions
TODAY20 years20 years
Your contributions¥7.2M
Change vs. contributions+¥5M
Goal progress100%
Plan for a goal
Goal progress after 20 years100%
Estimated goal year: 18
¥2.5MAround year 6
¥5MAround year 11
¥7.5MAround year 15
¥10MAround year 18
Monthly amount to reach this goal¥24,700
Add ¥5,000 a month
20-year difference+¥2M
Includes ¥1,200,000 in extra contributions
Compare accounts
NISA and taxable show after-tax values; iDeCo is before withdrawal tax.
Yearly breakdown
Pre-tax balance¥12,174,135
Total contributions¥7,200,000
Total fees¥0
Principal after fees¥7,200,000
Pre-tax return¥4,974,135
After-tax value¥12,174,135
| Year | Contributed | Projected assets | Tax estimate |
|---|---|---|---|
| Today | ¥0 | ¥0 | ¥0 |
| Year 1 | ¥360,000 | ¥368,177 | ¥0 |
| Year 2 | ¥720,000 | ¥754,764 | ¥0 |
| Year 3 | ¥1,080,000 | ¥1,160,679 | ¥0 |
| Year 4 | ¥1,440,000 | ¥1,586,890 | ¥0 |
| Year 5 | ¥1,800,000 | ¥2,034,412 | ¥0 |
| Year 6 | ¥2,160,000 | ¥2,504,310 | ¥0 |
| Year 7 | ¥2,520,000 | ¥2,997,703 | ¥0 |
| Year 8 | ¥2,880,000 | ¥3,515,765 | ¥0 |
| Year 9 | ¥3,240,000 | ¥4,059,731 | ¥0 |
| Year 10 | ¥3,600,000 | ¥4,630,895 | ¥0 |
| Year 11 | ¥3,960,000 | ¥5,230,617 | ¥0 |
| Year 12 | ¥4,320,000 | ¥5,860,325 | ¥0 |
| Year 13 | ¥4,680,000 | ¥6,521,519 | ¥0 |
| Year 14 | ¥5,040,000 | ¥7,215,772 | ¥0 |
| Year 15 | ¥5,400,000 | ¥7,944,738 | ¥0 |
| Year 16 | ¥5,760,000 | ¥8,710,152 | ¥0 |
| Year 17 | ¥6,120,000 | ¥9,513,837 | ¥0 |
| Year 18 | ¥6,480,000 | ¥10,357,706 | ¥0 |
| Year 19 | ¥6,840,000 | ¥11,243,769 | ¥0 |
| Year 20 | ¥7,200,000 | ¥12,174,135 | ¥0 |
Assumes a lump-sum sale at each year end. iDeCo withdrawal tax is not modeled.
Calculation method & sources
Historical index returns
Annualized compound returns (CAGR). Periods and dividend conventions differ. USD figures exclude changes in the yen exchange rate.
| Index | Annualized | Period / currency | Basis / source |
|---|---|---|---|
| Nasdaq-100 | 14.25% | –USD | Official compound annual return since launch. Dividend treatment is not specified in the article. Nasdaq |
| S&P 500 | ≈10% | –USD | Since launch, including dividends. The official brochure gives an approximate 10%. S&P Dow Jones Indices |
| Nikkei 225 (total return) | 6.34% | –JPY | Calculated from backfilled total-return data. Published from December 2012. Start 6,569.47; end 116,938.25. 日本経済新聞社 / Nikkei · Monthly data |
| All Country reference (MSCI ACWI) | 8.83% | –USD | MSCI ACWI gross total return, used as an All Country / Orukan reference. Includes backfilled data before its May 1990 launch; not the fund's JPY return. MSCI · All Country benchmark |
| Developed stocks (MSCI World) | 8.98% | –USD | Gross total return over the long-term period in the official factsheet, not the full period since launch. MSCI |
These are index returns, before fund expenses and foreign withholding taxes.
Calculation method
The annual return is effective: monthly rate = (1 + annual rate)^(1/12) − 1. Initial principal is invested at the start; contributions arrive at each month end. The rate stays constant. Fund expenses, inflation, and annual dividend taxes are excluded.
Taxable gains are taxed at a constant 20.315% on a lump-sum sale. NISA uses only the combined ¥3.6M annual and ¥18M lifetime limits; overflow is taxable. Separate slot limits, eligible products, and limit reuse after sales are not modeled.
iDeCo uses the caps from December 2026 throughout. Default fees are ¥2,829 initially and ¥186/month from the January 2027 debit. Excess contributions are excluded. Withdrawal taxes, age or eligibility restrictions, and iDeCo+ exceptions are not modeled. Funds are generally locked until age 60.
Estimated iDeCo tax saving = contributions × (marginal income-tax rate × 1.021 + 10% resident tax). Rates stay constant; bracket changes and insufficient taxable income are not modeled. Category 3 assumes no taxable income and no saving. Savings are kept separate from assets.
Goal years use year-end values. Required contributions round up to ¥100 for NISA/taxable accounts, or ¥1,000 with a ¥5,000 minimum for iDeCo.
Official references: FSA — NISA · MHLW — December 2026 rules · NTA — income-tax surtaxes
Shared links contain your amounts, goal, and other settings. Social images display the projected amount and conditions.
关于定投模拟器
Estimate future assets from monthly contributions, duration, and annual return. Presets cover Nasdaq-100, S&P 500, Nikkei 225 total return, MSCI ACWI, and MSCI World. Calculation method & sources shows each period and dividend convention.
Play the projection year by year or calculate the monthly amount needed for your goal. NISA and taxable accounts show after-tax values; iDeCo is before withdrawal tax. The iDeCo caps from December 2026 apply throughout the projection.
使用方法
- Choose NISA, iDeCo, or a taxable account
- Set monthly contributions, duration, and annual return
- Review projected assets and yearly growth
- Enter a goal to calculate required contributions
- Open Share plan to share a link or save an image
常见问题
What do the index return presets mean?
They are annualized compound historical returns (CAGR). S&P 500 is an official approximate figure; Nikkei 225 uses backfilled total-return data. MSCI World uses the long-term period in the official factsheet, not its full history since launch. See Calculation method & sources for periods, currencies, and dividend conventions.
What does the All Country / Orukan preset use?
It uses the long-term USD total return of MSCI ACWI as a reference for All Country / Orukan. Currency effects and expenses mean it differs from the fund's JPY performance.
How is compound growth calculated?
The entered return is effective annually. Monthly rate = (1 + annual rate)^(1/12) − 1. Principal is invested at the start and contributions at each month end. The rate stays constant; fund expenses and inflation are excluded.
Which NISA limits are modeled?
Only the combined ¥3.6M annual and ¥18M lifetime limits; overflow is taxable. Separate tsumitate (¥1.2M/year) and growth (¥2.4M/year, ¥12M lifetime) limits, eligible products, and limit reuse after sales are not modeled.
Which iDeCo contribution rules are used?
The rules from December 2026: ¥62,000/month for employees without a workplace pension, ¥75,000 combined with other pension payments for the self-employed, and ¥23,000 for Category 3. Workplace pension equivalents reduce the ¥62,000 cap. Defaults give public servants ¥54,000 and private-school staff ¥55,000. Age and eligibility restrictions are not checked.
Are iDeCo tax savings included in assets?
No. They are shown separately as contributions × (marginal income-tax rate × 1.021 + 10% resident tax). The 1.021 includes the combined income-tax surtaxes. Bracket changes and insufficient taxable income are not modeled. Category 3 assumes no taxable income and no saving. Withdrawal taxes are excluded.
How are taxes and fees handled?
Each year-end value assumes a lump-sum sale, with 20.315% tax on taxable gains. Loss offsets, annual dividend taxes, and trading fees are excluded. Only iDeCo deducts initial and monthly account fees; defaults are ¥2,829 and ¥186/month and can be changed.
How are required contributions calculated?
Using the same duration, return, taxes, and fees. Amounts round up to ¥100 for NISA/taxable accounts, or ¥1,000 with a ¥5,000 minimum for iDeCo. The goal year is the first year-end value at or above the target.
Can I save or share a plan?
Open Share plan to copy a link, share on X, or save a PNG image. A link opens the same settings in the simulator. Links and images include your amounts and other settings.