Jasmine Birtles
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New 4% AER*/tax-free** Cash ISA Launch Could Help Savers Lock In Tax-Free Interest for a Year
Monmouthshire Building Society has launched a new app-exclusive one-year fixed rate Cash ISA paying 4% AER tax-free – offering savers a simple way to lock in rates before potential rule changes ahead.
For anyone looking to make the most of their £20,000 annual ISA allowance, this new account could be an appealing option. It is designed for savers who want the certainty of a fixed return for the next 12 months, with the convenience of opening and managing the account through an app.
At a time when many savers are actively comparing the best Cash ISA rates, the launch stands out for combining a competitive fixed rate with the tax-free benefits that make ISAs such a popular savings choice.
At a glance
- Rate: 4% AER/tax-free fixed for one year
- Account type: App-exclusive one-year fixed rate Cash ISA
- Minimum deposit: £1,000
- Maximum balance: £20,000
- Eligibility: UK savers aged 18 and over
- Funding window: First 30 days after opening
- Transfers in: Not permitted
What the new Monmouthshire Building Society ISA offers
The new app-only fixed rate Cash ISA pays 4% AER tax-free for one year, giving customers a predictable return for the 12 months. The account is available only through the Monmouthshire Building Society app, reflecting the growing demand for digital-first money management.
Savers can open the ISA with a minimum of £1,000, and can deposit funds into the account within the first 30 days after opening. The maximum balance is £20,000, in line with the current annual ISA allowance.
Good to know
This ISA is for new ISA funds only, which means you cannot transfer in money from an existing ISA. That makes it best suited to savers planning to use fresh allowance rather than move old balances.
Why fixed-rate Cash ISAs remain popular
A fixed-rate Cash ISA can be especially attractive for savers who want certainty. Rather than worrying about rates moving up or down, customers know exactly what return they will get over the term, while also benefiting from the tax-free wrapper ISAs provide.
This can be particularly appealing for people who are cautious about investing and would rather keep their money in cash, while still making the most of a tax-efficient product.
Who could this suit?
- Savers who want a guaranteed return
- People who can leave money untouched for 12 months
- Anyone looking to use some or all of their 2026/27 ISA allowance
- Those who prefer managing savings through a mobile app
Important withdrawal rules to know
Because this is a one-year fixed-rate ISA, the money is intended to stay in place for the full term. Withdrawals cannot normally be made before maturity without a penalty.
If a saver does take money out early, a charge equivalent to 90 days’ loss of interest will be applied to the final balance. That means this account may be better suited to money that does not need to be accessed quickly.
Watch out for
Early access comes at a cost. If flexibility matters more to you than locking in a fixed rate, you may want to compare this account with an easy access Cash ISA instead.
A timely launch ahead of possible ISA changes
The launch also lands at a time when many savers are thinking carefully about how best to use their tax-free savings allowance.
Eleanor Crees, Savings Product Manager at Monmouthshire Building Society, said: “We are really proud to be bringing this app-only ISA product to the market, and with such a competitive interest rate.”
She added: “In the Autumn budget, it was announced that from April 2027 you will only be able to save up to £12,000 a year into a cash ISA if you are under 65 years of age. Therefore, the 2026/27 tax year will be the last chance that those under 65 will have to save up to £20,000 in a cash ISA.”
For savers considering their next move, that could make this tax year feel especially important when it comes to locking money into a competitive cash ISA rate.
App convenience with branch support
Although the account can only be opened via the Monmouthshire Building Society app, customers are not restricted to digital-only support once the account is up and running.
Crees said: “Thanks to our app, customers can control their finances from the palm of their hand, but once opened, they can also pop into our branches and hubs to manage their investments.”
That mix of digital convenience and in-person support may be particularly reassuring for customers who like the speed of app banking but still value the option of face-to-face help.
How to find out more
For more information about Monmouthshire Building Society’s fixed rate ISAs, visit the provider’s ISA page or download the app via Google Play or the Apple App Store.
The bottom line
For savers looking for a straightforward, tax-efficient home for their money, Monmouthshire Building Society’s new 4% one-year fixed rate Cash ISA could be a strong option. It offers the reassurance of a fixed return, the tax advantages of an ISA, and the convenience of app-based account opening.
While it will not suit everyone — especially those needing easy access or wanting to transfer old ISA funds — it may appeal to people looking to put fresh savings to work in a simple, structured way over the next year.
Disclaimer: This article is for informational purposes only and does not constitute financial advice. Rates, terms and product availability may change. Always read the full terms and conditions before opening any financial product.
Key facts
Rate: 4% AER/tax-free fixed for one year
Minimum deposit: £1,000
Maximum balance: £20,000
Access: App only
Withdrawals: Early access charge of 90 days’ loss of interest
* AER stands for Annual Equivalent Rate and illustrates what the interest rate would be if interest was paid and compounded once each year.
** The tax-free rate means that interest is exempt from income tax.
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