Finding the best Cash ISA means looking beyond the headline rate. The right account depends on whether you want instant access, a fixed term, or the flexibility to withdraw and replace within the tax year. With the Cash ISA allowance for under-65s reducing to £12,000 from April 2027, the 2026/27 tax year is the last opportunity to maximise the full £20,000 in cash — making it one of the most important ISA decisions in years.
What makes a good Cash ISA?
The AER
The Annual Equivalent Rate (AER) is the standard measure for comparing savings rates fairly. It accounts for compounding, making it the most accurate figure to use when comparing providers. Always compare AER, not the gross rate.
Easy access vs fixed rate
Easy access Cash ISAs let you withdraw freely — ideal for emergency funds and short-term goals. Fixed rate Cash ISAs lock your money away for a set term in exchange for a higher guaranteed rate — better for money you won’t need for a year or more. See our guides to Cash ISAs, easy access accounts and fixed rate accounts for a full comparison.
Flexible ISA feature
A flexible Cash ISA lets you withdraw and replace money within the same tax year without it counting toward your annual allowance again. This is valuable if you might need to dip in temporarily. Not all providers offer this — check before opening.
Introductory bonus rates
Some providers offer a higher rate for the first 12 months, which then drops. Always check what the rate reverts to and set a reminder to review and potentially transfer to a better deal when the bonus ends.
FSCS protection
Always confirm your Cash ISA provider is covered by the Financial Services Compensation Scheme (FSCS), which protects up to £85,000 per person, per institution. If you have more than £85,000 to shelter, consider splitting across multiple providers.
Why 2026/27 is the most important ISA year for a generation
This is the last tax year in which under-65s can contribute the full £20,000 to a Cash ISA. From April 2027 the limit drops to £12,000. At the same time, savings income tax rates are rising by two percentage points across all bands from April 2027 — taking the basic rate to 22% and the higher rate to 42%. This makes sheltering savings inside an ISA more valuable than at any point in recent years.
If you have savings sitting in a standard account and haven’t used your 2026/27 ISA allowance, moving them into a Cash ISA before 5 April 2027 locks in the maximum tax-free cash position permanently — existing ISA balances are unaffected by the new rules.
Cash ISA vs standard savings account
The best Cash ISA rates are often competitive with — and sometimes better than — the best standard savings accounts. And all interest is tax-free. With savings tax rates rising from April 2027, the advantage of a Cash ISA over a standard account will increase further. For a full comparison, see our guide to Cash ISA vs savings account.
How much interest will I earn?
Use our savings calculator to see exactly what your balance would earn at different ISA rates — and to compare the after-tax difference between a Cash ISA and a standard savings account.
Frequently asked questions
What is the maximum I can put in a Cash ISA in 2026/27?
The maximum is £20,000 — the full annual ISA allowance. From April 2027, this reduces to £12,000 for under-65s. Savers aged 65 and over retain the full £20,000 limit.
Can I have more than one Cash ISA?
Yes — since April 2024 you can pay into multiple Cash ISAs with different providers in the same tax year, as long as your total contributions don’t exceed £20,000 in 2026/27.
Is it worth switching Cash ISA providers?
Often yes. Providers regularly reduce rates for existing customers while offering better deals for new ones. See our guide to how to transfer an ISA — the process takes as little as 15 working days and preserves your full tax-free wrapper.
How do I find the best Cash ISA rate?
Compare AER across providers using comparison sites such as MoneySavingExpert or Moneyfacts, which are updated regularly. Rates change frequently — check at least once a year and especially when the Bank of England adjusts its base rate.