Cash ISA interest rates are climbing sharply as a torrent of deposits flood the market, giving savers a powerful window to protect their cash before the Government slashes the cash ISA tax-free allowance next year for under-65s.
New analysis* from Investec Save reveals that the average rate for the top 30 one-year fixed cash ISAs jumped to 4.49% AER**, up from 4.36% AER in April and just 4.03% AER in February. This rapid three-month surge has added 0.46% to top-tier market returns, intensifying competition among banks and building societies.
The rate momentum coincides with unprecedented demand for tax-free cash shelters. It has been predicted that total net inflows into cash ISAs could grow by as much as 20% this tax year, potentially pushing annual cash-specific ISA deposits to an all-time record of £85 billion***.
Leading the charge, Investec Save recently increased its 1-Year Fixed Rate Cash ISA to 4.56% AER**, up from 4.52%. The move underscores a highly competitive battlefield for fixed-rate cash ISA deposits as savers scramble to maximise returns before legislative changes reduce the amount under-65s can save into a cash ISA from April 2027.
David Hunt, Head of Savings, Investec Bank, said: “We are witnessing an extraordinary flight to fixed-rate cash ISAs as savers look to lock in peak guaranteed returns. This historic wave of deposits is driven by dual motivation. Savers want to stay ahead of inflation while taking full advantage of the current tax rules. Our decision to boost our 1-Year Fixed ISA to a competitive 4.56% AER** ensures that clients can maximise their tax-free growth at a time when guaranteed yield has rarely been more valuable.”
Under current rules, savers can shield up to £20,000 across their ISAs each year. However, from 6th April 2027, the dedicated cash ISA tax-free allowance for under-65s will fall dramatically to £12,000. While the overall aggregate ISA limit will remain at £20,000, the shifting rules mean this financial year represents the final opportunity for most savers to deploy the full £20,000 threshold strictly into cash ISAs.
Investec Save’s 1-Year Fixed Rate Cash ISA enables customers to lock in fixed rates for longer, helping them grow their savings and make the most of their tax-free ISA allowance each tax year. It can be opened with a minimum of £1,000 and customers earn tax-free interest on deposits fixed for one year.
Investec Save’s range of accounts can be opened online in minutes and are fully managed online with no hidden fees or charges. As well as the Fixed Rate Cash ISA, they include a Fixed Rate Saver with 1-Year offering 4.40% AER**, 2-Years offering 4.50% AER** or 3-Years offering 4.55% AER** Interest is paid on maturity of the 1-Year term and annually on the 2-Year and 3-Year terms. No withdrawals are permitted until the end of the term in each case, and no further deposits can be made after the first seven days.
A 90-Day Notice Saver is also available, which currently offers 4.00% AER**, offers unlimited deposits with withdrawals subject to 90-days’ notice. This is ideal for those expenses that you can plan for, such as a holiday or wedding.
In addition, the Online Flexi Saver, which currently offers 3.79% AER**, is a simple and secure instant access savings account. Unlimited deposits and withdrawals are allowed. This makes the Online Flexi Saver worth considering for unexpected expenses that might arise, such as car maintenance or a vet bill.
- *Investec Save analysis of Moneyfacts data https://moneyfactscompare.co.uk/isa/ correct as of May 19th 2026
- **AER stands for the Annual Equivalent Rate and illustrates what the interest rate would be if interest was paid and compounded once a year. The AER is intended to be an indicative rate to help you compare the return on different savings products.
- ***https://www.lloydsbankinggroup.com/media/press-releases/2026/lloyds/isa-savings-worth-1-trillion.html
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