NISA Calculator

About This NISA Calculator

This calculator projects the growth of investments inside a NISA (shogaku toshi hikazei seido) tax-free account and compares it against a standard taxable account. It uses the New NISA rules introduced in January 2024 and performs monthly compounding calculations with deferred taxation modeling.

Enter your monthly contribution amount, expected annual return rate, and investment period. The calculator shows your total contributions, final NISA balance, taxable account balance after capital gains tax, tax saved, and the total difference between the two paths.

The most important number the calculator produces is the gap between your NISA balance and your taxable-account balance at the end of the period. That gap is pure tax savings — money you would have handed to the government that instead stays in your account and compounds. Over 20 or 30 years, even at a modest 5 percent return, the difference runs into millions of yen, because the deferred capital-gains tax at the end of a taxable account still takes a sizeable slice.

The calculator also warns you when your inputs approach or exceed the legal limits. New NISA caps annual contributions at 3.6 million yen and lifetime contributions at 18 million yen, with a sub-cap of 12 million yen for the growth-investment frame. If you enter a monthly contribution that would breach these limits, you will see a clear warning explaining which year you hit the ceiling.

YenWise builds each tool for expats who need numbers they can explain to an employer, a tax accountant, or themselves. We document official sources, show intermediate steps where it matters, and flag every simplification. Use the calculator as a planning layer on top of primary documents (源泉徴収票, ねんきん定期便, brokerage statements), not as a substitute for them.

Who Should Use This Calculator

This tool is designed for anyone investing, or considering investing, in Japanese stocks or mutual funds through a NISA account:

If you are new to investing in Japan, start here before opening a brokerage account: seeing the long-term math makes the decision to invest far less intimidating. If you are already investing, use the calculator to compare your current monthly contribution against what your limits allow, and to stress-test different return assumptions before committing to a number.

If you are comparing job offers, planning a move within Japan, or preparing for year-end tax adjustment (年末調整) or final return (確定申告), run two or three scenarios side by side and save or screenshot the results for your records.

• •Expats building long-term wealth in Japan through NISA-eligible investments
• •Beginners comparing the tax advantage of NISA versus a regular taxable brokerage account
• •Investors planning their monthly contribution strategy within the New NISA lifetime limits
• •Anyone cross-checking payslips, pension notices, or brokerage statements against official rules

How the New NISA System Works (2024+)

The New NISA, launched in January 2024, dramatically expanded the tax-free investment framework. The lifetime contribution limit is 18 million yen, with up to 12 million yen allocatable to growth investments. Investments inside NISA are permanently exempt from Japan's 20.315% capital gains tax (20% income tax plus 0.315% reconstruction surtax).

A critical distinction in this calculator: Japanese taxable accounts use deferred taxation. Capital gains are taxed only at the time of sale, not annually. Many calculators incorrectly apply tax every year, which dramatically understates the taxable account final value. This calculator applies the 20.315% tax only once, at the end of the investment period, on the total gain.

The calculator uses an annuity-due compounding model where contributions grow from the first day of each month. This produces slightly higher returns than ordinary annuity calculations and accurately reflects how real monthly investment plans work.

The lifetime limit in New NISA is tracked on a book-value (purchase-amount) basis, not market value. When you sell an investment and withdraw the proceeds, that portion of your lifetime limit frees up again for future use — this is the reusable framework that distinguishes New NISA from the old system. The calculator does not model withdrawals and reuse, but it is worth understanding because it means the lifetime limit is far less constraining than it first appears.

After you change an input, results update in the browser only — nothing is uploaded. Shareable URL parameters (where enabled) encode your scenario so you can reopen the same numbers later or send them to a spouse or accountant without creating an account.

Methodology & review

Growth is modeled with monthly contributions (annuity-due style) and a user-set expected return. Tax-free NISA outcomes are compared against a taxable account using Japan’s approximate capital-gains tax burden so you can see the deferred-tax gap. Annual and lifetime contribution caps reflect the new NISA framework documented in our limits config.

Each tool is reviewed when underlying rules change (for example Reiwa-year tax reforms, NISA contribution caps, or pension premium tables) and whenever we expand the long-form explanation. The “Last reviewed” date on the page is the date of the latest substantive content or formula review.

We distinguish three kinds of numbers: (1) exact under the stated statute, (2) statutory estimates with known caps, and (3) planning assumptions you control. Assumptions such as expected investment return or remaining working years are never hidden inside a black box.

• •Primary sources linked in the Sources section below
• •Browser-side calculation — inputs stay on your device
• •Editorial review date shown in the byline above the tool

Important Notes

The expected return rate is an assumption you provide. Historically, global equity markets have returned approximately 5-8% annually after inflation, but past performance does not guarantee future results. Consider running multiple scenarios with conservative and optimistic rates.

The 18 million yen lifetime limit applies to total contributions across both the tsumitate and growth investment frames combined. Once you reach the lifetime cap, no new contributions are allowed, though existing investments continue growing tax-free indefinitely.

Investment returns are not smooth. The calculator applies a constant annual rate, but real markets deliver years of +20 percent gains and -30 percent losses in unpredictable sequences. Over long horizons the average matters most, but if you are within five years of needing the money, sequence risk dominates and a single bad year can be hard to recover from. Treat the projection as a central estimate, not a guarantee.

Local city-tax nuances, special deductions (medical, housing loan credit details, foreign tax credits), and employer-specific social insurance rates can differ from simplified models. When your situation is complex, take the YenWise breakdown to a zeirishi or FP and adjust inputs using your actual forms.

Getting the Most From the New NISA

A few principles tend to produce better outcomes than trying to time the market:

• •Prioritize the tsumitate (regular-savings) frame first — it has the lower 1.2-million-yen annual limit but is built for low-cost index funds and disciplined monthly investing.
• •Stay invested through market downturns. The biggest tax savings come from years of compounded gains, and missing the best recovery days destroys long-term returns.
• •Use the growth frame for individual stocks or sector funds you have researched, not for speculative bets — the tax exemption is most valuable on long-term winners.
• •Reinvest dividends rather than spending them; inside NISA they compound tax-free, which is the single most powerful feature of the account.
• •Review your allocation annually but avoid frequent trading — the framework rewards patience, and transaction costs erode returns.
• •Bookmark the page with your scenario filled in, and re-run after any salary change, bonus, or rule update so your plan stays current.

Official Sources and Further Reading

• Financial Services Agency — New NISA Portal
• Financial Services Agency — NISA Statistics
• Tokyo Stock Exchange — NISA Guide