Second marriages and the children from the first: protecting what matters

Office for National Statistics data shows that in 2020, 20% of opposite-sex marriages were remarriages for at least one partner. Among older couples the figure is higher. Remarriage is common, and so is the financial complexity that comes with it: assets accumulated in a previous life, children from a previous relationship, and a new partner whose long-term interests may not align perfectly with those children's.

The legal default in second marriages can lead to a result almost no one would actively choose: the unintended disinheritance of children from the first marriage. Here is how it happens and how to address it.

The mechanism: sideways disinheritance

Suppose Alex remarries Sam, having two children from a first marriage. Alex makes a will leaving everything to Sam, trusting that Sam will pass it on to Alex's children in due course. Sam then makes a will leaving everything to Sam's own children, or remarries, or simply changes their mind after Alex dies. Alex's children inherit nothing.

This pattern, sometimes called sideways disinheritance, is one of the most common sources of family dispute on second deaths. It is not malicious; it is what happens when nothing is written down to prevent it.

The tools that prevent it

Three structures, often used together, address sideways disinheritance:

1. Life interest trust in your will

A life interest (or "interest in possession") trust lets the surviving spouse live in the family home and benefit from the income of a trust fund during their lifetime, while the capital ultimately passes to the beneficiaries you named (your children). The surviving spouse cannot redirect that capital to anyone else.

2. Mirror wills with mutual obligations

Mirror wills are commonly written by spouses leaving everything to each other, then on the second death to specified beneficiaries. They are simple but easily revoked by the survivor. Mutual wills (a stronger version that binds the survivor) are uncommon in modern practice because of disputes about whether the agreement was genuinely mutual.

3. Postnuptial agreement or private financial agreement

A postnup, or a private financial agreement, written by spouses already married, can set out what each partner agreed about premarital assets, inheritance intentions, and financial arrangements on death. The Supreme Court treated postnups on the same footing as prenups in MacLeod v MacLeod [2008] UKPC 64 and subsequent cases. The principles from Radmacher v Granatino [2010] UKSC 42 apply.

For couples blending families, the postnup is the document that records who brought what, what is being kept separate, and what is being merged.

Inheritance tax considerations

The spouse exemption means transfers between spouses or civil partners are exempt from inheritance tax. That is helpful in the short term but does not solve the long-term planning problem. Using a life interest trust can preserve the nil rate band of the first spouse to die for the benefit of the children, and is a common structure for second marriages.

The residence nil rate band (an additional inheritance tax allowance available when a main residence is left to direct descendants) has specific rules for second marriages and step-children. Specialist advice is worth the cost.

The conversation to have

Practically, every couple in a second marriage should have an explicit, written discussion that covers:

• What each partner brought into the marriage, listed and valued
• Which assets are intended to remain with the family of origin (typically children from the first marriage)
• Which assets are now shared, and how
• The order of inheritance (what passes to the spouse, what passes directly to children, in what form)
• Provision for the surviving spouse's housing and income

A postnup or private financial agreement captures the answers. Mirror wills, life interest trusts, and updated pension nominations implement them. Without that structure, the law's default will fill in the blanks, and it rarely fills them in the way the family expected.