iDeCo Tax Savings Calculator (個人型確定拠出年金)

About This iDeCo Calculator

This calculator shows how much tax you save by contributing to iDeCo (kojingata kakutei kyoshutsu nenkin — individual-type defined contribution pension). It also projects your retirement balance and compares it against a taxable investment account over the same period.

Select your employment category to see your monthly contribution limit, enter your salary to calculate tax savings, and set your investment assumptions. The calculator displays your marginal tax rate, annual tax savings, net monthly cost, and long-term growth projection.

The headline benefit of iDeCo is the upfront income-tax deduction: every yen you contribute reduces your taxable income for the year, which lowers both national income tax and residence tax. For a typical mid-career employee in the 20 percent bracket, that means roughly 30 percent of each contribution comes back as tax savings — making the effective cost of contributing far lower than the sticker price.

The trade-off is a long lock-up: iDeCo funds cannot be accessed until age 60 under normal circumstances. That makes it a poor fit for short-term savings but an excellent fit for retirement planning, especially for expats who expect to stay in Japan long enough to benefit. The calculator shows both the annual tax savings and the projected balance at age 60, so you can weigh the immediate benefit against the long-term constraint.

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 considering iDeCo as a tax-efficient retirement savings vehicle in Japan:

iDeCo is most attractive for higher earners in elevated tax brackets, for whom the deduction is worth the most. It is less compelling for very low earners (where the deduction saves little and the lock-up is a real cost) and for people who may need liquidity before age 60. A common strategy is to max out iDeCo first for the tax deduction, then use NISA for additional savings that remain accessible.

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.

• •Company employees looking for additional tax deductions beyond NISA and dependent exemptions
• •Self-employed individuals who want to maximize their pension contributions and tax savings
• •Long-term residents planning for retirement with locked-in tax-advantaged savings
• •Anyone cross-checking payslips, pension notices, or brokerage statements against official rules

How iDeCo Tax Savings Work

iDeCo contributions are fully deductible from your taxable income (zengaku shotoku kojo). This means every yen you contribute reduces both your national income tax and your residence tax. The exact savings depend on your marginal tax rate, which is determined by your income bracket.

Your tax savings rate is calculated as: marginal income tax rate times 1.021 (reconstruction surtax) plus 10% (residence tax). For example, if your marginal income tax rate is 20%, your total tax savings rate is approximately 30.42% (20% times 1.021 plus 10%). This means nearly a third of your contribution comes back as tax savings.

Monthly contribution limits depend on your employment category: self-employed (Category 1) can contribute 68,000 yen/month; company employees without a corporate DC plan (Category 2) can contribute 23,000 yen/month; those with a company DC plan get 12,000 yen/month. Funds are locked until age 60.

Monthly contribution limits are set by your employment category and are surprisingly specific: self-employed workers (Category 1) can contribute up to 68,000 yen per month; company employees without a corporate DC plan (Category 2) up to 23,000 yen; employees whose company already offers a DC plan up to 12,000 yen; and dependent spouses (Category 3) up to 23,000 yen. The calculator enforces these caps and shows the exact limit for your selected category.

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

Contribution ceilings depend on pension category (employee, public servant, self-employed, etc.). Tax savings estimate marginal income tax plus residence tax effects of the deduction; projections to age 60 use your assumed return and compare with a taxable account where shown.

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

iDeCo funds are locked until age 60. Early withdrawal is not possible under normal circumstances. If you leave Japan permanently, a lump-sum withdrawal may be available but is taxed as ordinary income. Consider this lock-up period carefully before enrolling.

The retirement projection uses monthly compounding (annuity-due model) and compares iDeCo against a taxable account with deferred 20.315% capital gains tax. Actual investment returns depend on your chosen fund allocations and market performance.

At age 60, iDeCo funds can be withdrawn as a lump sum, as a pension, or as a combination — and withdrawals are taxed as retirement income (taishoku shotoku) with a generous deduction based on years of service. For most long-term contributors, the effective tax on withdrawal is low or zero. However, if you leave Japan permanently before age 60, an early lump-sum withdrawal may be possible but is taxed as ordinary income, which can erase much of the upfront benefit — an important caveat for expats uncertain about their long-term plans.

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.

Using iDeCo Effectively

Because of the long lock-up, small decisions at the start matter a lot:

• •Contribute the maximum your category allows — the tax deduction scales with contribution size, and leaving headroom wastes the benefit.
• •Choose low-cost index funds inside iDeCo; the original offerings had high fees, but low-cost global equity funds are now widely available.
• •Combine iDeCo with NISA: iDeCo for the tax deduction and discipline, NISA for liquidity and additional tax-free growth.
• •Factor in the monthly administration fee (typically a few hundred yen) when projecting net returns over decades.
• •If you might leave Japan before 60, model the early-withdrawal scenario first — the lock-up is the single biggest risk for expats.
• •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

• National Tax Agency — iDeCo Portal
• iDeCo Official — National Pension Fund Association
• Financial Services Agency — Defined Contribution Pension