The Hidden Inheritance Rule Worth More Than Half a Million
When Margaret Thompson's husband died in 2025, she inherited his £340,000 ISA portfolio — but lost the tax wrapper protecting it from HMRC. Or so she thought.
Photo: Margaret Thompson, via images.squarespace-cdn.com
Eighteen months later, Margaret discovered the Additional Permitted Subscription (APS) allowance, a little-known inheritance rule that would have let her shelter her late husband's entire ISA value inside her own tax-free wrapper. The 180-day window to claim it had long passed.
"Nobody mentioned it," says Margaret. "Not the bank, not the solicitor, not even our financial adviser. I could have saved thousands in tax."
She's not alone. HMRC data suggests fewer than 15% of eligible surviving spouses actually claim their APS allowance, despite it being worth up to £685,000 in additional tax-free savings capacity.
What Is the Additional Permitted Subscription?
The APS allowance works like this: when your spouse or civil partner dies, you inherit not just their ISA assets, but also their ISA allowance.
If your partner had built up £200,000 in ISAs over their lifetime, you can contribute an additional £200,000 to your own ISAs on top of your annual £20,000 limit — effectively doubling your tax-free capacity.
The maximum possible APS claim is £685,000, representing the cumulative ISA allowances available since the scheme launched in 1999 (accounting for the various annual limits over time).
This isn't automatic. You must actively claim the APS allowance, and you have just 180 days from either the date of death or when the ISA administration is completed, whichever is later.
The 180-Day Trap
The tight deadline catches most families off guard. Unlike other inheritance processes that can take months or years, the APS clock starts ticking immediately.
"Families are dealing with grief, probate, funeral arrangements," explains Sarah Mitchell, a chartered financial planner at Quilter. "The last thing on their mind is obscure ISA rules. By the time they're ready to think about financial planning, the window has often closed."
The deadline is inflexible. HMRC offers no extensions, even in complex probate cases.
Platform Lottery: Who Makes It Easy, Who Doesn't
Not all ISA providers handle APS claims equally. Our research reveals stark differences:
Smooth operators:
- Hargreaves Lansdown: Dedicated APS team, clear online guidance, typically processes claims within 10 working days
- AJ Bell: Proactive contact with bereaved customers, streamlined paperwork
- Interactive Investor: Automatic flagging system alerts customer services to potential APS cases
Problem platforms:
- Several high street banks require multiple branch visits and paper forms
- Some online platforms lack dedicated APS processes, leading to months-long delays
- One major provider we contacted couldn't initially explain what APS was
"The quality of service varies enormously," says Tom McPhail from The Lang Cat consultancy. "Some platforms see APS as a customer service priority. Others treat it as an administrative burden."
Photo: Tom McPhail Lang Cat consultant, via thelangcat.co.uk
The Real-World Numbers
Consider a typical scenario: John and Mary, both 65, each hold ISAs worth £150,000. When John dies, Mary faces two choices:
Without APS: John's £150,000 loses its tax wrapper. Assuming 4% annual growth, Mary pays tax on roughly £6,000 per year in investment gains — £120,000 over 20 years at higher-rate tax.
With APS: Mary claims John's £150,000 APS allowance, keeping everything tax-free. The saving: £120,000 over two decades.
For couples with larger ISA pots, the numbers become substantial. A surviving spouse inheriting £400,000 in ISAs could save £320,000 in tax over their remaining lifetime.
The Documentation Challenge
Claiming APS requires specific paperwork:
- Death certificate
- Proof of marriage or civil partnership
- Details of all the deceased's ISA holdings
- Valuation statements as of date of death
The complexity increases if your partner held ISAs with multiple providers. Each requires separate APS applications, and you must track down every account.
"We see cases where people miss ISAs they didn't know existed," says Mitchell. "An old workplace savings scheme, a forgotten Cash ISA from years ago. Each one represents additional APS allowance."
What to Do Right Now
If you've recently been bereaved:
- Contact every ISA provider immediately — don't wait for probate to complete
- Ask specifically about APS allowances and the 180-day deadline
- Request written confirmation of your APS entitlement
- Consider professional advice if dealing with multiple providers
For planning ahead:
- Keep a master list of all ISA accounts and providers
- Ensure your spouse knows about APS rules
- Consider consolidating ISAs with APS-friendly platforms
- Include APS instructions in your will or letter of wishes
The Government's Silence
Despite APS being worth hundreds of thousands to eligible families, government guidance remains minimal. The official HMRC page runs to just 400 words, with no worked examples or practical advice.
"It's almost like they don't want people to know about it," suggests one financial adviser who asked not to be named. "The more people claim APS, the less inheritance tax and capital gains tax the Treasury collects."
The Bottom Line
The APS allowance represents one of the most valuable yet overlooked tax breaks in the UK system. For eligible couples, it's worth more than most people's pension pots.
Yet the combination of poor awareness, tight deadlines, and inconsistent platform support means the majority of families miss out entirely.
If you're married or in a civil partnership with significant ISA holdings, understanding APS isn't just helpful — it's essential financial planning that could save your family hundreds of thousands in tax.
This article is for informational purposes only and does not constitute financial advice. Your capital is at risk. Past performance is not a reliable indicator of future results.