SEISEI INSIGHTS — Succession
Why a Will Does Not Settle It: Japan's Reserved Portion
2026-08-31
"There is a will. It leaves everything to our second son. Do my daughter and I simply have to accept it?" We hear versions of this question repeatedly when families come to us about succession. A will carries real force in Japan. The reserved portion does not make a disposition that exceeds it void; what the Civil Code reserves for a defined group of heirs is standing to claim money to the extent their reserved portion is impaired. That is why a will does not necessarily play out as written — the mechanism is the reserved portion, or iryūbun.
What a Will Can Do
Article 964 of the Civil Code provides that a testator "may dispose of the whole or part of their property by comprehensive or specific title." Article 902(1) further allows the decedent to designate the shares of co-heirs by will. Who receives what is, as a starting point, the testator's decision.
Who Holds a Reserved Portion, and How Much
Article 1042 is what constrains that freedom in its effect. It governs who holds a reserved portion and in what proportion; it neither prohibits nor invalidates a testamentary disposition that exceeds it. Its consequence takes the form of the monetary claim under Article 1046, discussed below. Paragraph 1 provides that "heirs other than siblings" receive, as their reserved portion, the value of the property base for calculating the reserved portion multiplied by the applicable ratio: one-third where only lineal ascendants are heirs, and one-half in all other cases. Paragraph 2 provides that where there are several heirs, that ratio is further multiplied by each heir's own share calculated under Articles 900 and 901.
| Composition of heirs | Aggregate reserved portion | Each heir's entitlement |
|---|---|---|
| Spouse and children | One-half of the calculation base (Art. 1042(1)(ii)) | One-half multiplied by each heir's statutory share (Art. 1042(2)) |
| Lineal ascendants only | One-third (Art. 1042(1)(i)) | One-third multiplied by each heir's statutory share (Art. 1042(2)) |
| Siblings | No provision — Art. 1042(1) reads "heirs other than siblings" | — |
Two premises matter. A spouse is always an heir (Art. 890), and children are heirs under Article 887(1). Lineal ascendants become heirs only where there is no person who would be an heir under Article 887 (Art. 889(1)(i)). Consequently, where a spouse and children exist, no matter where a will attempts to concentrate the estate, one-half of the calculation base remains as reserved portion.
What the Calculation Is Built On
Article 1043(1) defines the base as the value of property the decedent held at the commencement of succession, plus the value of property they gave away, minus the full amount of debts. The point is that the base is not limited to what remained at death.
Article 1044 sets which gifts are added back. Paragraph 1 limits this to gifts made within one year before the commencement of succession — but where both parties knew the gift would harm a reserved-portion holder, earlier gifts are included as well. Paragraph 3 then substitutes "ten years" for "one year" in the case of gifts to heirs, limited to gifts received "for marriage or adoption, or as capital for livelihood." In families that have made sustained lifetime gifts, this ten-year reach often determines the outcome.
The Claim Is for Money
Article 1046(1) provides that a reserved-portion holder and their successors may demand from a legatee or donee "payment of money equivalent to the amount of the infringement." The claim is monetary. It is not a claim to recover the real estate or the shares themselves.
Seen from the paying side, this is a liquidity question. Article 1047(1) caps what a legatee or donee bears at the value of what they received — and, by the parenthetical in that same paragraph, where the legatee or donee is themselves an heir, at that value less the amount they are entitled to receive as their own reserved portion under Article 1042. Article 1047(5) provides that "the court may, at the request of the legatee or donee, grant a reasonable period of grace for payment of all or part of the obligation." Where a design concentrates company shares or the family home in one successor, whether that successor can actually raise the cash determines whether the design is workable at all.
The Time Limits
Under Article 1048, the claim for the reserved-portion infringement amount is extinguished by prescription if not exercised within one year from the time the holder learns of both the commencement of succession and the gift or bequest that infringes the reserved portion. The same applies once ten years have passed from the commencement of succession.
What Can Be Addressed in Advance
The reserved portion is not beyond advance planning. Article 1049(1) provides that a waiver of the reserved portion before the commencement of succession "takes effect only where the approval of the family court has been obtained." A private agreement among the parties produces no effect; the family court procedure is required. Under Article 1049(2), a waiver by one co-heir does not affect the reserved portions of the others.
Treat It as a Structural Question
In our experience, most disputes surrounding a will arise less from its contents than from the fact that the reserved portion was never built into the design. Three points to confirm at the design stage:
- Who will hold a reserved portion — the composition of heirs determines whether the aggregate is one-half, one-third, or unprovided for
- Which gifts to heirs over the past ten years were made for marriage or adoption, or as capital for livelihood — under Article 1044(3), this is what changes the calculation base
- Whether the concentrated successor can meet a monetary demand — the Article 1046 claim is a money claim
A will becomes an executable design only once the composition of heirs, the history of lifetime gifts, and post-succession liquidity are mapped onto a single structural diagram.
This article provides general information on legal and tax systems and does not constitute individual legal or tax consultation. Specific filings and tax computations are handled by licensed partner tax accountants whom we introduce; the handling of actual disputes over the reserved portion falls within the practice of attorneys.