How should a couple structure ISAs to maximise tax-free income?

01 Two allowances, both expiring

Each individual has a £20,000 ISA allowance and it does not carry forward. A couple with £24,000 to invest can put £20,000 into one ISA and £4,000 into the other, or £12,000 into each — and only the second uses both allowances.

Over a decade that difference compounds into a substantial gap in how much of the household's wealth sits inside a tax wrapper. It is not about which partner should own the money; it is about the room expiring.

There is no mechanism to recover an unused allowance, which is what makes this an annual discipline rather than a one-off decision.

On the defaults above, the worked example shows £28,000. Using one allowance shelters £20,000; using both shelters £28,000, and the difference cannot be recovered later.

Source: Individual Savings Accounts (ISAs)

02 There is no joint ISA

ISAs are individual accounts by law. A couple cannot hold one jointly, cannot transfer between each other's ISAs, and cannot pool the allowances. Money moving from one partner's ISA to the other's is a withdrawal and a fresh subscription.

That means the household's tax-free wealth is divided between two people from the outset, and the division is permanent in the sense that it cannot be rebalanced without using allowance.

In practice this argues for keeping the two ISAs roughly balanced as they grow, because a very lopsided pair is harder to draw on efficiently in retirement and leaves one partner with little tax-free income of their own.

There is one exception worth knowing. A Lifetime ISA has its own £4,000 sub-limit inside the £20,000, and only one partner may be eligible if the other is over 40. That asymmetry is a reason to fund the eligible partner's Lifetime ISA first and use the rest of the household's allowance elsewhere.

Source: MoneyHelper: ISAs

03 Cash to fund both

Where only one partner has income, the other's allowance is funded by a gift between spouses, which is free of tax and unlimited. Nothing about the money's origin affects the subscription, so a single-earner household can still use both allowances in full.

The same applies to a lump sum. Splitting an inheritance or a bonus across both ISAs, and across a 5 April boundary, can shelter £80,000 in a matter of weeks rather than £20,000 in a year.

The gift is real, as it is with contributions to a spouse's pension — the money becomes theirs. For most couples that is not an obstacle, and it should be understood rather than assumed.

Source: Capital Gains Tax on gifts

04 Drawing on them in retirement

Two ISAs give a household two sources of tax-free capital, and in retirement that is what makes withdrawal sequencing work: pension income up to each partner's personal allowance, topped up from whichever ISA suits.

A balanced pair means either partner can fund the top-up, which matters if one dies or if their income positions diverge. A lopsided pair concentrates the flexibility in one person's hands.

The survivor's position is also protected by the additional permitted subscription, which lets a surviving spouse rewrap the deceased's ISA on top of their own allowance. That entitlement has to be claimed and is regularly missed.

The point about balance has a tax edge as well as a practical one. In retirement, ISA money is the flexible top-up that lets pension withdrawals stop at a band boundary, and that only works if the partner who needs to stop has ISA money of their own. A single large ISA in one name leaves the other partner with pension income and nothing to blend it with.

Source: Inheriting ISAs

05 An annual routine

Each January, check what has been subscribed to each ISA this tax year and fund whichever is behind. Where money is short, split it rather than concentrating it, because the smaller allowance is the one that expires.

Then check the balance between the two accounts and direct the following year's subscriptions toward whichever is smaller, so the pair converges over time rather than diverging.

And subscribe before 5 April even without an investment decision. Cash can be subscribed into a stocks and shares ISA and invested later, which secures the room while leaving the decision open.

Finally, check the two accounts are not accidentally holding the same thing. Couples who fund two ISAs with the same fund at the same provider have doubled the allowance and not the diversification, which is a missed opportunity rather than a risk — but an easy one to correct at the point of subscribing.

Source: Individual Savings Accounts (ISAs)