Best Cash ISA Rates in the UK for September 2026
The Cash ISA market currently spans promotional easy access rates above 5% and longer fixed terms around 5.25%. The right comparison keeps rate, access and transfer rules on separate lines so a high AER is not mistaken for a universally better ISA.
Where the highest Cash ISA rates currently sit
Trading 212 currently advertises a 5.01% AER variable promotional Cash ISA rate for eligible new customers, including a temporary 1.41 percentage point bonus on qualifying current-year subscriptions. Moneyfacts' 25 September market snapshot also placed Trading 212 at the top of the easy access Cash ISA table.
For fixed terms, Shawbrook currently advertises 5.25% AER on its five-year Fixed Rate Cash ISA, 4.99% on two years and 4.83% on one year. Moneyfacts similarly reported 5.25% as the top fixed Cash ISA rate in late September.
These figures answer only the rate question. Trading 212's headline promo treatment differs for transfers, while a five-year Shawbrook fix removes access for much longer. The best rate for fresh emergency savings can therefore be a poor fit for an existing ISA transfer or a known two-year spending goal.
Translate rate differences into pounds before moving money
On £10,000, 5.01% is roughly £501 of interest over a year if the rate stayed unchanged. At 4.50%, the same balance produces about £450. The difference is approximately £51, which gives a realistic price for the half-percentage-point gap.
On £50,000, that same 0.51 percentage point difference is roughly £255 over a year. The rate becomes more important as the balance grows, but transfer eligibility and FSCS concentration also become more important.
A saver should therefore compare both the rate gap and the operational cost of moving. A £51 annual advantage is not worth losing flexible access or paying a large fixed-term penalty if the money is likely to be needed. Repeat the calculation after any promotional bonus ends. A one-year headline can look attractive while the second-year base rate is much lower, so put the post-bonus rate and expected interest in a separate line before opening the account.
Fresh subscriptions and transfers can earn different rates
Trading 212's current promotional guidance says the promotional uplift does not apply to money transferred from another ISA provider. A rate table that shows 5.01% without that qualification can therefore overstate the return available on an existing ISA pot.
Moneybox accepts transfers from multiple ISA types but currently advertises a lower new-customer rate than the top promotional accounts. Shawbrook accepts historic ISA transfers into its Cash ISA range, including fixed products, up to product-specific maximum balances.
Build separate columns for fresh current-year money and transferred existing ISA money. If the account treats those pots differently, calculate the expected interest separately rather than quoting one headline AER for the entire balance. If you hold both fresh 2026/27 money and a transferred historic ISA balance, ask the provider whether the two pots receive the same rate. Where they do not, calculate the return on each pot separately rather than averaging them into one headline figure.
Tax-free does not automatically beat a taxable savings account
The Cash ISA advantage depends partly on whether you would otherwise pay tax on savings interest. A basic-rate taxpayer with unused Personal Savings Allowance may be able to earn some taxable savings interest without paying tax, while a high-balance saver can exhaust the allowance quickly.
Compare the after-tax return outside an ISA with the tax-free return inside. If a taxable savings account pays materially more, the ISA can still win for someone whose interest is taxable, but it may not win for someone whose savings interest remains below their allowance.
The ISA wrapper also has long-term value because historic balances remain sheltered and can be transferred between providers. That makes the tax decision broader than one year's headline rate. A higher-rate taxpayer or someone with a large cash balance can use the Personal Savings Allowance quickly, making the tax-free wrapper more valuable. A basic-rate saver with modest interest may care more about the gross rate and access. The comparison should therefore use the saver’s likely tax position rather than treating 'tax-free' as a fixed cash bonus.
Keep the 2027 Cash ISA change out of today's rate calculation
The current 2026/27 overall ISA subscription limit is still £20,000. From 6 April 2027, under-65s face a £12,000 Cash ISA subscription limit while the overall ISA allowance remains £20,000.
Do not reduce a September 2026 subscription calculation to £12,000. The new cash cap starts in the next tax year. Existing ISA balances and formal transfers are also different from new annual subscriptions.
For current decisions, use the 2026/27 rules. For planning beyond 5 April 2027, show the new limit separately so readers can see that the law changes at a defined tax-year boundary. If you are planning contributions across both tax years, create two separate rows: one for money subscribed before 6 April 2027 under the current rules and another for subscriptions from 6 April onward. That prevents next year’s £12,000 under-65 cash cap from being applied prematurely to a current-year deposit.
BankOfferScout editorial view
A strong Cash ISA combines a competitive tax-free return with transfer and access rules that fit the saver. We do not treat the highest displayed rate as automatically superior when the wrapper or liquidity becomes harder to use.
With Best Cash ISA Rates, our conclusion is anchored in usable value, conditions and likely behaviour. We stress-test the comparison for moving or withdrawing money in a way that undermines the intended ISA treatment. If two options are close, simpler conditions and a better fit for normal behaviour can be more valuable than a marginal numerical edge that is easy to lose. The relevant test on this page is the cash balance, access need and transfer plan.
With Best Cash ISA Rates, our conclusion is anchored in usable value, conditions and likely behaviour. The last step is freshness. Confirm AER, bonus periods, transfer acceptance, withdrawal terms, account availability and provider procedures on the provider ISA summary box, transfer terms and current product conditions; where a scheme, tax or regulatory rule matters, use HMRC or another authoritative ISA source as well. The final application, transfer or switch should always use current information.
Sources and related guides
Rate figures were checked on 30 September 2026 against Trading 212, Shawbrook, Moneyfacts and GOV.UK. Future updates should refresh the live AER, promotional terms, transfer treatment and product access at the same time. Rate tables should distinguish fresh subscriptions from transferred ISA money whenever the provider does.
- Trading 212 - Cash ISA
- Trading 212 - promotional rate rules
- Shawbrook - Cash ISA rates
- Moneyfacts - current ISA rates
- GOV.UK - ISA overview
Related Guides: Future updates should refresh easy access and fixed rates on the same date, verify whether quoted promotional rates apply to transfers, and keep the operative tax year beside every allowance figure. A rate table should not mix a fresh-money promo, a transfer rate and a fixed term without labelling the conditions that make those numbers comparable.