Japan iDeCo Calculator: Defined-Contribution Pension Growth
Estimate what a Japanese iDeCo (individual-type defined contribution pension) grows to from regular monthly contributions — the private pension where contributions are tax-deductible and investment growth is tax-free.
Adjust the inputs and select Calculate for a full breakdown.
Year-by-year growth schedule
Compare Common Scenarios
How the numbers shift across typical situations for this calculator:
| Scenario | Future value | Total contributions | Total interest earned |
|---|---|---|---|
| ¥23k/mo · 3% · 25yr | $10,258,179.93 | $6,900,000.00 | $3,358,179.93 |
| ¥12k/mo · 3% · 30yr | $6,992,842.62 | $4,320,000.00 | $2,672,842.62 |
| ¥68k/mo · 4% · 20yr (self-employed) | $24,940,674.57 | $16,320,000.00 | $8,620,674.57 |
| ¥1M + ¥20k/mo · 5% · 15yr | $7,459,482.81 | $4,600,000.00 | $2,859,482.81 |
How This Calculator Works
Enter your current iDeCo balance, monthly contribution, the return you expect, and the years contributing. The calculator compounds the balance monthly and shows the projected value and the growth. iDeCo is a retirement account: your contributions reduce taxable income now, the investments grow tax-free, and the money is locked until age 60.
The Formula
Future Value with Regular Contributions
P = starting amount, PMT = monthly contribution, r = monthly rate (annual ÷ 12), n = number of months
Worked Example
¥23,000 a month for 25 years at 3% grows to about ¥10,258,180, with roughly ¥3,358,180 of that being tax-free growth. iDeCo (individual-type Defined Contribution pension) is Japan's tax-advantaged private pension. It has a triple tax benefit: contributions are fully deductible from taxable income (cutting income and resident tax), gains compound tax-free inside the account, and withdrawals from age 60 receive favourable tax treatment via the retirement-income or public-pension deductions. The monthly contribution ceiling depends on your employment type.
Key Insight
iDeCo is the retirement-focused complement to NISA in Japan's savings system, and its tax design is what sets it apart. The triple advantage: (1) contributions are deductible from taxable income, so every yen paid in reduces your income tax and resident tax that year — a benefit NISA doesn't offer; (2) investment gains compound free of the ~20% tax that applies in a regular brokerage account; and (3) at withdrawal from age 60, the payout is taxed favourably — as a lump sum it uses the generous retirement-income deduction (taishoku shotoku kōjo), or as an annuity it uses the public-pension deduction. The key trade-off versus NISA is liquidity: iDeCo funds are locked until 60 (you generally can't withdraw early), so it suits money you're genuinely setting aside for retirement, while NISA stays accessible. Contribution ceilings differ by status — self-employed (No.1 insured) have the highest monthly cap, company employees vary depending on whether they also have a corporate DC/DB plan, and civil servants and homemakers (No.3) have lower caps — so confirm your limit before maximising. Costs matter more than in NISA because iDeCo charges account-management fees (to the National Pension Fund Association and the record-keeper) on top of fund fees, which drag on small balances, so low-cost index funds and consistent contributions are favoured. This calculator gives a gross, constant-return projection and omits fees, the contribution cap, and withdrawal tax; in practice the upfront tax deduction effectively boosts your real return, the cap limits monthly input, fees reduce the balance slightly, and the age-60 lock means you should treat iDeCo as untouchable until retirement. A common strategy is to use both: iDeCo for the contribution tax deduction on retirement money, and NISA for flexible tax-free investing.
The tax saving on every yen contributed
The signature feature of iDeCo is that every yen of your contribution is deducted from taxable income for BOTH national income tax and 10% resident tax. So someone in a low income bracket (5% income tax + 10% resident = 15% combined) who contributes ¥10,000/month saves roughly ¥18,000/year in tax. Someone at the top bracket (45% income tax + 10% resident = 55% combined) saves ¥66,000/year on the same contribution.
Concrete example for a mid-career employee on ¥5M of taxable income (20% income tax + 10% resident = 30% combined): contributing the standard Category 2 cap of ¥23,000/month (¥276,000/year) saves ¥82,800/year in tax — an immediate 30% boost effectively converting the contribution into ¥358,800 of pre-tax investment.
The saving is realised at year-end through the year-end adjustment (年末調整) for salaried employees or the annual tax return (確定申告) for the self-employed. The savings compound: every yen of tax saved is yen you can immediately invest elsewhere (NISA, taxable account) or spend on other priorities.
Contribution ceilings by employment category
Japan's pension system has three categories that determine the iDeCo monthly cap. Category 1 (No.1 insured: self-employed, freelancers, university students 20+): ¥68,000/month — the highest cap, designed to compensate for the absence of a corporate or government pension.
Category 2 (employees and civil servants): splits further. Private-sector employees without a corporate DC/DB plan: ¥23,000/month. With a corporate DC plan: ¥20,000. With a corporate DB plan (or both): ¥12,000. Civil servants: ¥12,000. The 2024 reform aimed to harmonise these upward over time.
Category 3 (No.3 insured: dependent spouses of Category 2): ¥23,000/month — but for these contributors the tax deduction has limited value since they typically have no taxable income themselves. iDeCo here serves more as a forced retirement saving plus tax-free growth than as a tax shelter.
Withdrawal at 60: lump-sum or annuity tax treatment
iDeCo cannot be withdrawn before age 60 (with very narrow exceptions for permanent disability or death). At 60+, you choose between three withdrawal forms: full lump sum, annuity, or a mix.
Lump-sum withdrawal uses the retirement-income deduction (taishoku shotoku kōjo), which is highly generous: roughly ¥400,000 × years of contribution (rises to ¥700,000 × years beyond 20 years). For someone who contributed for 30 years, the deduction is around ¥15M — meaning the first ¥15M of the lump sum is effectively tax-free.
Annuity withdrawal uses the public-pension deduction (kōteki nenkin tō kōjo), which is also generous but spread over each year of payout. For most iDeCo participants, taking the corpus as a lump sum (or a partial lump sum + reduced annuity) wins on total tax — but if you have a large company retirement payout in the same year, splitting iDeCo as an annuity over multiple years avoids stacking up against the retirement deduction.
Annual tax saving from iDeCo by income bracket and monthly contribution
Combined income tax + 10% resident tax. Income tax brackets shown are for taxable income (after deductions): 5% up to ¥1.95M, 10% to ¥3.30M, 20% to ¥6.95M, 23% to ¥9M, 33% to ¥18M, 40% to ¥40M, 45% above.
| Income tax bracket | ¥12k/mo | ¥23k/mo | ¥68k/mo |
|---|---|---|---|
| 5% (15% combined) | ¥21,600 | ¥41,400 | ¥122,400 |
| 10% (20% combined) | ¥28,800 | ¥55,200 | ¥163,200 |
| 20% (30% combined) | ¥43,200 | ¥82,800 | ¥244,800 |
| 23% (33% combined) | ¥47,520 | ¥91,080 | ¥269,280 |
| 33% (43% combined) | ¥61,920 | ¥118,680 | ¥350,880 |
| 40% (50% combined) | ¥72,000 | ¥138,000 | ¥408,000 |
| 45% (55% combined) | ¥79,200 | ¥151,800 | ¥448,800 |
Annual saving = monthly contribution × 12 × combined tax rate. This is realised once a year through year-end adjustment or tax return.
Frequently Asked Questions
How is iDeCo growth calculated?
Your balance and monthly contributions compound at the expected return (annual rate ÷ 12 per month). ¥23,000/month for 25 years at 3% grows to about ¥10,258,180, with roughly ¥3,358,180 of tax-free growth — before account and fund fees.
What is iDeCo?
Japan's individual-type defined contribution pension — a tax-advantaged private pension. Contributions are deductible from taxable income, investment gains compound tax-free, and withdrawals from age 60 get favourable tax treatment. The money is locked until 60, which distinguishes it from the more flexible NISA.
How is iDeCo different from NISA?
iDeCo adds an upfront tax deduction on contributions (NISA doesn't) but locks the money until age 60. NISA has no contribution deduction but stays fully accessible and also offers tax-free growth. Many Japanese savers use both: iDeCo for retirement with the deduction, NISA for flexible tax-free investing.
How much can I contribute to iDeCo?
It depends on your employment type. The self-employed have the highest monthly ceiling; company employees vary depending on whether they also have a corporate pension; civil servants and dependent spouses have lower caps. This calculator doesn't enforce the limit, so confirm your category's ceiling.
When can I withdraw iDeCo?
Generally from age 60 — iDeCo is a retirement pension and the funds are locked until then, with only narrow exceptions. At withdrawal, a lump sum uses the retirement-income deduction and an annuity uses the public-pension deduction, both favourable. Treat iDeCo money as untouchable until retirement.
References & Authoritative Sources
- National Pension Fund Association (iDeCo Official) — iDeCo Official Site — eligibility, contribution caps, fund options · consulted May 31, 2026 · Government-designated operator — authoritative source on iDeCo by Category 1/2/3
- Ministry of Health, Labour and Welfare (MHLW) — Individual-type Defined Contribution Pension — policy and reforms · consulted May 31, 2026 · Regulator — 2024 reform raising Category 2 contribution caps
- National Tax Agency of Japan — Small-scale corporate mutual aid deduction (covers iDeCo) · consulted May 31, 2026 · Tax administration — full deductibility of iDeCo contributions
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Methodology & Review
The future value compounds a starting balance plus a fixed monthly contribution at the annual return, compounded monthly. It assumes a constant return and end-of-month deposits, and does not enforce the iDeCo monthly contribution ceiling (which varies by employment type), model fund fees, or compute the tax due when the pension is withdrawn.
Reviewed according to the CalcDomain Editorial Policy & Calculator Methodology. We document formulas, edge cases, sources, update dates, and correction paths for calculator pages.
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