Enter your taxable income, contributor type, and monthly contribution to estimate your annual tax savings from contributing to iDeCo (Japan’s individual defined contribution pension).
Japan iDeCo Tax Deduction Calculator
Applies your contributor-type contribution cap and marginal tax rate to estimate savings
Check your “kazei hyojun” (taxable income base) on your gensen choshuhyo (withholding tax slip). If unsure, a rough estimate is about 65-70% of your gross annual salary.
* This calculator assumes your full iDeCo contribution is deductible and applies only your marginal tax rate — a simplified estimate. Actual tax savings depend on interactions with your other deductions and how you file (nenmatsu chosei or kakutei shinkoku). Confirm the exact figure with a tax accountant.
How to Use This Calculator
- Enter your taxable income — not your gross salary, but the amount left after employment income deduction, social insurance deduction, and other deductions.
- Select your contributor type — this automatically applies the correct monthly iDeCo contribution cap. Limits shown reflect the rules in effect as of 2026 (before the December 2026 reform).
- Enter your monthly contribution and click Calculate to see your recognized contribution, marginal rate, and estimated annual tax savings.
How the Calculation Works
iDeCo contributions are fully deductible from taxable income, so your tax savings can be estimated as your annual contribution × your marginal rate (income tax + resident tax). Your marginal rate is the rate applied to your top bracket of income — the higher your income bracket, the greater your savings for the same contribution.
Estimated savings = min(annual contribution, contributor-type annual cap) × (marginal income tax rate × 1.021 + 10% resident tax)
The 1.021 multiplier accounts for the special reconstruction income tax (2.1% of your income tax liability, in effect through 2037). Resident tax is applied as a flat approximately 10%, regardless of income bracket.
Monthly Contribution Caps by Contributor Type (as of 2026)
| Contributor Type | Monthly Cap | Annual Cap |
|---|---|---|
| Company employee (no corporate pension) | JPY 23,000 | JPY 276,000 |
| Civil servant / employee with corporate DB pension | JPY 20,000 | JPY 240,000 |
| Self-employed (combined with National Pension Fund) | JPY 68,000 | JPY 816,000 |
Note: Following a December 2026 reform (expected to apply from January 2027 contributions), caps are set to rise to JPY 75,000/month for the self-employed and JPY 62,000/month for employees and civil servants. This calculator applies the caps in effect as of July 2026.
Marginal Rate Table (Income Tax + Resident Tax, Including Reconstruction Surtax)
| Taxable Income | Combined Marginal Rate |
|---|---|
| Up to JPY 1.95M | ~15.1% |
| JPY 1.95M-3.3M | ~20.2% |
| JPY 3.3M-6.95M | ~30.4% |
| JPY 6.95M-9M | ~33.5% |
| JPY 9M-18M | ~43.7% |
| JPY 18M-40M | ~50.8% |
| Over JPY 40M | ~55.9% |
For a full introduction to iDeCo — eligibility, how withdrawals work, and how it compares to a 401(k) — see our guide:
Meet iDeCo, Japan’s Answer to a 401(k) →
Sources
Figures and requirements in this article were verified against the primary sources below. Rules change, so check the originals before you enroll or contribute. (Verified 15 Aug 2026)
- MHLW — iDeCo changes from December 2026 (Japanese) current caps by member type and the December 2026 reform
- MHLW — iDeCo cap raised from JPY 12,000 to 20,000 (Dec 2024, Japanese) JPY 20,000/month and JPY 240,000/year for civil servants and DB members
- iDeCo official site (NPFA) — eligibility, contributions, payouts (Japanese) age requirements by member category and payout start age
- NTA No.1135 — Small Business Mutual Aid contribution deduction (Japanese) the full amount paid in the year is deductible
Frequently Asked Questions
Q. Should I just enter my gross annual salary as taxable income?
A. Not recommended. The taxable income field is your tax base after deductions like the employment income deduction and social insurance deduction, not your gross salary. Check the ‘kazei hyojun’ figure on your withholding slip, or roughly estimate it as 65-70% of your gross salary if you’re unsure.
Q. What happens if my monthly contribution exceeds the cap?
A. iDeCo doesn’t allow contributions above your contributor type’s monthly cap in the first place. This calculator flags the excess with a warning and only counts contributions up to the cap when estimating your tax savings.
Q. I’m a company employee enrolled in a corporate DC plan — which type should I pick?
A. If you’re enrolled in a company-sponsored defined contribution (DC) plan, your allowed iDeCo contribution may be capped differently (e.g., JPY 20,000/month) depending on your company’s plan rules. The ‘civil servant / DB pension’ option here is meant for defined benefit (DB) plan participants and civil servants — DC plan participants should confirm their exact cap with HR or their iDeCo provider.
Q. Does this calculator show my exact refund amount?
A. No. This is a simplified estimate that multiplies your iDeCo contribution by your marginal tax rate. Your actual tax savings depend on your other deductions and credits and how you file (year-end adjustment or final tax return), so treat this as a reference figure only.
Key Takeaways
- iDeCo contributions are fully tax-deductible; savings are estimated as recognized annual contribution × marginal rate (income tax + resident tax).
- As of July 2026, monthly caps are JPY 23,000 for company employees (no corporate pension), JPY 20,000 for civil servants/DB plan members, and JPY 68,000 for the self-employed.
- Caps are set to rise after a December 2026 reform (effective January 2027 contributions) — check for the latest official announcement.
- The higher your income bracket, the larger your tax savings for the same contribution amount.
This article and calculator are for general informational purposes only. Actual tax savings depend on your overall income, deductions, and filing method. Confirm specifics with a licensed tax accountant.