But fixing your Isa now could protect your savings from future rate cuts and help you make the most of the current cash Isa allowance before new rules come in next year.
Here, we take a closer look at what might be behind the decline in popularity and explain how fixing could help you prepare for upcoming changes to tax-free savings.
Why did interest in fixed-rate cash Isas dip?
The main advantage of fixing your cash Isa is that you're protected from any potential rate cuts. That's unlike instant-access products, which have a variable rate that can go up or down at short notice.
However, new data suggests savers are turning away from fixed Isas. Moneyfacts analysis shows that the proportion of customers using its site to find one of these accounts dropped from 26% to 19% between April and May.
On the other hand, demand for instant-access Isas surged to around 32% – up from 24% in April.
So what's going on? Rachel Springall, Moneyfacts finance expert, told Which? that market volatility and rumours of a rise in the Bank of England base rate could be why savers were on the fence about locking into a fixed rate last month.
The drop in appetite for fixed cash Isas in May might also be down to the fact that there's generally a surge in demand at the beginning of the new financial year in April. Providers often launch competitive deals at the start of the tax year to attract savers looking to maximise their annual £20,000 Isa allowance.
Find out more:Can fixing beat next year's savings shake-up?
From 6 April 2027, major changes will come into force that will impact savers with larger nest eggs.
Opening a fixed-rate cash Isa could be a good way to side-step the new rules – at least temporarily. Money already held in a cash Isa will keep its tax-free status, and the new limits will apply to money paid in from April 2027 onwards.
It means you could, in theory, fix for five years and not have to worry about the changes until the account matures in 2031.
Find out more:Where can you find the best cash Isa deal?
Now is also a great time to grab a top fixed Isa deal, with rates climbing to their highest level since 2024.
Average interest on a one-year fixed cash Isa climbed from 4.17% AER to 4.25% in the month to 1 June. Products lasting more than one year saw average rates increase from 4.14% to 4.22% over the same period.
Instant-access cash Isas saw a slight dip in average rates – from 2.76% on 1 May to 2.74% on 1 June.
This table shows the top cash Isa accounts, ordered by term:
| Isa type | Provider | Account name | Interest rate (AER) | Provider customer score | Minimum investment | Opening methods | Interest paid |
|---|---|---|---|---|---|---|---|
| Instant access | Atom Bank | Easy Access Cash ISA | 4.25% | 76% | £0 | Mobile app | Monthly |
| One-year fixed rate | Investec Save | Fixed Rate Cash ISA | 4.68% | n/a | £1,000 | Internet | On maturity |
| Two-year fixed rate | Castle Trust Bank | Fixed Rate e-Cash ISA | 4.72% | n/a | £1,000 | Internet, mobile app | On maturity |
| Three-year fixed rate | Castle Trust Bank | Fixed Rate e-Cash ISA | 4.68% | n/a | £1,000 | Internet, mobile app | On maturity |
| Four-year fixed rate | United Trust Bank | Cash ISA 4 Year Bond | 4% | n/a | £5,000 | Internet | Anniversary |
| Five-year fixed rate | Castle Trust Bank | Fixed Rate e-Cash ISA | 4.72% | n/a | £1,000 | Internet, mobile app | On maturity |