Why allocations drift, calendar vs threshold rebalancing, using contributions, and NISA vs taxable considerations.
Rebalancing restores your target stock/bond weights after markets move them; the tax-efficient way is to direct new contributions toward the under-weighted asset, selling only when necessary — and preferring NISA trades or cash flows over realising taxable gains.
You choose a target mix — say 60% equities, 40% bonds — because it matches how much risk you want. But markets move the pieces at different rates: after a strong equity run, that 60/40 might become 70/30, quietly making your portfolio riskier than you intended. After a crash it might become 50/50, more conservative than planned. Rebalancing restores the target so your risk stays where you decided.
Rebalancing is a discipline, not a return-boosting trick. Its main value is keeping risk aligned with your plan and enforcing "sell high, buy low" mechanically, rather than acting on emotion.
Two common rules exist. Calendar rebalancing checks and resets on a schedule — for example once a year. Threshold rebalancing acts only when an asset drifts beyond a band — for example rebalancing a 60/40 target when equities exceed 65% or fall below 55%. Many investors combine them: review on a calendar but only trade if a threshold is breached, to avoid needless small trades.
The most tax- and cost-efficient method is rebalancing with new contributions: direct fresh monthly money toward whichever asset is under-weighted, nudging the mix back without selling anything. For accumulating investors, this alone often keeps the allocation within band.
Where you rebalance matters for tax. In a taxable account, selling a winner to rebalance realises a gain that is taxed at 20.315%, so prefer using new contributions, dividends, or cash flows first. Inside NISA, selling does not create Japanese tax, but the repurchase consumes annual allowance and the sold lifetime capacity only returns next year — so contributions are still usually the better tool.
A practical priority order: rebalance with new contributions where possible; then use NISA trades (no tax, but mind allowance); then, only if needed, sell in the taxable account, accepting the tax. Keep the process simple and infrequent — over-rebalancing adds cost and effort without improving results.
Brokerage (NISA/iDeCo) · Rakuten Securities
A leading low-cost brokerage for NISA and index-fund investing, integrated with Rakuten points and Rakuten Bank.
Fees: Many domestic funds and trades are low- or no-commission — verify current fee schedule.
Brokerage (NISA/iDeCo) · SBI Securities
Japan’s largest online brokerage by accounts, with a very broad low-cost fund lineup and full NISA/iDeCo support.
Fees: Many trades and funds are low- or no-commission — verify current fee schedule.
Brokerage (NISA/iDeCo) · Monex
An established online brokerage often chosen for US-stock access and research tools, with NISA and iDeCo support.
Fees: Commissions vary by product; some funds/trades are low-cost — verify current schedule.
This is education, not a recommendation. Most beginners research low-cost, broadly diversified index funds — for example all-country (全世界株式) or S&P 500 trackers — rather than picking individual stocks, because low fees and diversification are within your control while returns are not. Understand that values fall as well as rise, match the risk to your time horizon, and never invest money you may need soon.