Cash ISA Rates: How to Compare UK Rates Today

Detailed comparison framework

Cash ISA rate research should separate the tax wrapper from the savings product. The best headline AER can be less useful if it applies only temporarily, blocks transfers or requires access conditions that conflict with the money's purpose.

Translate every Cash ISA rate into pounds on the same balance

Use one balance and one holding period for the first comparison. On £10,000, a 4.00% AER rate is roughly £400 over a year and 5.00% is roughly £500 if the balance and rate stayed unchanged. The one percentage point gap is about £100.

This simple conversion shows whether a rate difference is material. A 0.10 percentage point edge on £2,000 is only about £2 a year, while the same edge on £100,000 is about £100.

Rate tables should therefore show the qualifying balance and the likely holding period. A percentage alone does not tell the saver how many tax-free pounds the product may generate.

For Cash ISA Rates: How to Compare UK Rates Today, this section should be tested against the reader's actual balance, dates and normal behaviour rather than a provider maximum or generic example. The controlling idea is that Cash ISA rate value depends on qualifying balance, rate structure, tax position, access and transfer treatment. Record the source date and the assumption behind section 1, then run one downside case: a missed condition, lower balance, delayed payment, changed rate, unavailable channel or earlier need for the money. If the conclusion changes materially under that ordinary stress case, the headline feature should receive less weight. This keeps 'Translate every Cash ISA rate into pounds on the same balance' tied to usable pounds and operational outcomes instead of marketing language.

Separate variable, bonus and fixed rates before ranking them

Trading 212 currently advertises a 5.01% AER variable promotional Cash ISA rate for eligible new customers under its current offer structure, while Shawbrook's one-year Fixed Rate Cash ISA currently pays 4.83% AER fixed. These rates solve different problems.

A promotional variable rate can change and has an expiry structure. A fixed rate provides certainty but restricts access and can impose exit costs. The correct ranking depends on whether the saver needs liquidity or certainty rather than on the larger percentage alone.

Record rate type, bonus end date, fixed maturity date and any post-promotion rate in separate fields. This prevents a temporary rate from being modelled as though it lasts forever.

For Cash ISA Rates: How to Compare UK Rates Today, this section should be tested against the reader's actual balance, dates and normal behaviour rather than a provider maximum or generic example. The controlling idea is that Cash ISA rate value depends on qualifying balance, rate structure, tax position, access and transfer treatment. Record the source date and the assumption behind section 2, then run one downside case: a missed condition, lower balance, delayed payment, changed rate, unavailable channel or earlier need for the money. If the conclusion changes materially under that ordinary stress case, the headline feature should receive less weight. This keeps 'Separate variable, bonus and fixed rates before ranking them' tied to usable pounds and operational outcomes instead of marketing language.

Transfer treatment can change the rate available to an existing ISA balance

Some promotions apply differently to new subscriptions and transfers. Trading 212's current promotional guidance distinguishes qualifying current-tax-year subscriptions from money transferred from another ISA provider.

A saver moving £50,000 of historic ISA money should therefore verify the rate on transferred funds rather than assuming the new-money headline applies to the full balance.

Transfer support, partial-transfer rules and the effective rate on transferred money belong in the same shortlist as AER. Existing ISA wealth can make transfer treatment more important than the fresh-subscription offer.

For Cash ISA Rates: How to Compare UK Rates Today, this section should be tested against the reader's actual balance, dates and normal behaviour rather than a provider maximum or generic example. The controlling idea is that Cash ISA rate value depends on qualifying balance, rate structure, tax position, access and transfer treatment. Record the source date and the assumption behind section 3, then run one downside case: a missed condition, lower balance, delayed payment, changed rate, unavailable channel or earlier need for the money. If the conclusion changes materially under that ordinary stress case, the headline feature should receive less weight. This keeps 'Transfer treatment can change the rate available to an existing ISA balance' tied to usable pounds and operational outcomes instead of marketing language.

Compare the Cash ISA with taxable savings only after estimating tax

ISA interest is tax-free, but ordinary savings can sometimes pay a higher gross rate. The correct comparison uses the saver’s likely after-tax return outside the ISA, taking current savings allowances into account.

A saver who expects all ordinary savings interest to remain within their Personal Savings Allowance may need a materially higher Cash ISA rate before the wrapper creates extra first-year value. A saver already using that allowance can value the tax shelter more highly.

Do not use one universal 'ISA beats savings' rule. Separate rate, tax position and access, then compare the final pounds available under each structure.

For Cash ISA Rates: How to Compare UK Rates Today, this section should be tested against the reader's actual balance, dates and normal behaviour rather than a provider maximum or generic example. The controlling idea is that Cash ISA rate value depends on qualifying balance, rate structure, tax position, access and transfer treatment. Record the source date and the assumption behind section 4, then run one downside case: a missed condition, lower balance, delayed payment, changed rate, unavailable channel or earlier need for the money. If the conclusion changes materially under that ordinary stress case, the headline feature should receive less weight. This keeps 'Compare the Cash ISA with taxable savings only after estimating tax' tied to usable pounds and operational outcomes instead of marketing language.

Keep 2026/27 rates separate from the 2027 allowance reform

The current 2026/27 overall ISA subscription limit is £20,000. HMRC confirms that from 6 April 2027 under-65s will have a £12,000 Cash ISA subscription cap within the overall £20,000 ISA limit, while people aged 65 or over keep a £20,000 Cash ISA limit.

That reform changes how much new cash can be subscribed, not whether today's 2026/27 rate comparison should use a £12,000 cap early.

Date every allowance statement and every live rate. Product pricing can change daily while tax rules change on specified effective dates, so both layers need separate freshness controls.

For Cash ISA Rates: How to Compare UK Rates Today, this section should be tested against the reader's actual balance, dates and normal behaviour rather than a provider maximum or generic example. The controlling idea is that Cash ISA rate value depends on qualifying balance, rate structure, tax position, access and transfer treatment. Record the source date and the assumption behind section 5, then run one downside case: a missed condition, lower balance, delayed payment, changed rate, unavailable channel or earlier need for the money. If the conclusion changes materially under that ordinary stress case, the headline feature should receive less weight. This keeps 'Keep 2026/27 rates separate from the 2027 allowance reform' tied to usable pounds and operational outcomes instead of marketing language.

Sources and related guides

Cash ISA rate guidance was checked on 30 September 2026 against live BankOfferScout, Trading 212, Shawbrook, GOV.UK and HMRC sources. Future updates should refresh AER, rate type, bonus expiry, transfer treatment, balance rules and tax-year limits independently. The hub should continue to distinguish a live product quote from the durable method of comparing tax-free and taxable savings returns.

For Cash ISA Rates: How to Compare UK Rates Today, this section should be tested against the reader's actual balance, dates and normal behaviour rather than a provider maximum or generic example. The controlling idea is that Cash ISA rate value depends on qualifying balance, rate structure, tax position, access and transfer treatment. Record the source date and the assumption behind section 6, then run one downside case: a missed condition, lower balance, delayed payment, changed rate, unavailable channel or earlier need for the money. If the conclusion changes materially under that ordinary stress case, the headline feature should receive less weight. This keeps 'Sources and related guides' tied to usable pounds and operational outcomes instead of marketing language.

• BankOfferScout - Cash ISA Rates
• Trading 212 - Cash ISA
• Shawbrook - 1 Year Fixed Rate Cash ISA
• GOV.UK - ISA overview
• HMRC - September 2026 tax-free savings newsletter

Related Guides:

• Best Cash ISA Rates
• How Cash ISA Interest Works
• Easy Access Cash ISAs