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Is bonus interest on a Cash ISA taxable?

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UKPublished 6 October 2026 · Written by BuyMeWhiskey Editorial Team · How we check facts

If a bonus is genuinely interest credited within a valid ISA, it is normally covered by the ISA tax exemption. A separate reward paid outside the ISA can have different treatment, so check the product terms and statement description.

Next question: How is bank interest calculated daily and paid monthly? →

Check the GOV.UK ISA rules and your provider’s terms to confirm whether a bonus is part of the ISA or paid separately.

Check how ISA interest is taxed

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The ISA wrapper is the starting point

GOV.UK says you do not pay tax on interest in an ISA and do not need to declare ISA interest on a tax return. That principle generally covers ordinary interest earned inside a Cash ISA.

The complication comes from the word bonus. A provider can describe a payment as a bonus, reward or promotional rate, and the tax treatment depends on what the payment actually is and where it is paid. The label alone is not enough.

Bonus interest versus a separate reward

Suppose a Cash ISA pays a higher introductory interest rate for a period. If that rate is part of the Cash ISA interest credited to the account, it remains inside the ISA wrapper and is treated like the account’s other ISA interest.

By contrast, a provider might pay a separate reward to a current account, investment account or another non-ISA destination. That reward can have different tax treatment because it is not automatically protected just because you happen to hold an ISA with the same provider.

Check the statement description

Look at where the money was credited. If the amount increased the Cash ISA balance and is described as interest, that points towards it being part of the ISA return. If it arrived as a separate payment into a current account, ask the provider what the payment represents and whether it is taxable.

For a disputed tax question, keep the product terms, screenshots and statement entry. You may need to show exactly what the provider promised and how the reward was paid.

Do the Personal Savings Allowance rules matter?

The Personal Savings Allowance applies to taxable savings income, not to interest that is already exempt because it arises within an ISA. HMRC’s published savings-income rates for 2026/27 include a £1,000 Personal Savings Allowance for basic-rate taxpayers and £500 for higher-rate taxpayers, subject to the stated rules.

So you should not count ISA interest against your Personal Savings Allowance. The allowance is relevant to savings outside the ISA wrapper.

Does the 2027 Cash ISA reform change the tax treatment of existing ISA interest?

The main 2027 change is about annual Cash ISA subscriptions for people under 65, not about suddenly making existing ISA interest taxable. From 6 April 2027, under-65s will have a £12,000 annual Cash ISA subscription limit, within the overall £20,000 ISA limit.

HMRC has also introduced anti-circumvention rules for cash held in Stocks and Shares and Innovative Finance ISAs. Those rules are aimed at discouraging long-term cash holdings outside a Cash ISA, but they do not turn ordinary Cash ISA interest into taxable bank interest.

What should you ask a provider about a bonus?

Is the payment interest, a reward, cashback or another type of payment?
Is it credited to the ISA or to a separate account?
Does it count towards the advertised interest rate?
Is there any condition such as maintaining a balance or transferring in funds?
Will the provider issue a tax statement for the payment?

These questions are more useful than asking whether a “bonus” is taxable in the abstract.

What if the bonus changes the advertised rate?

A time-limited bonus rate can affect the economic value of the account without changing its tax wrapper. For example, the first part of the year might pay a promotional rate and the rest might pay a lower standard rate. Your comparison should use the terms and dates actually applying to the account.

Do not quote or rely on an old forum post giving a particular provider’s bonus percentage. Promotions expire; the lasting question is whether the payment is ISA interest or a separate taxable reward.

What if the provider pays the bonus outside the ISA?

That is the point at which the tax answer can change. A separate payment outside the wrapper may fall under the ordinary rules for taxable income or savings income, depending on its nature.

Ask the provider to confirm the tax character of the payment in writing if the statement does not make it clear. If the amount is significant, consider checking HMRC guidance or obtaining professional tax advice based on the exact terms.

The practical answer

Do not focus on the word “bonus”. First establish whether the payment is ISA interest credited inside the ISA. If it is, the ISA wrapper normally protects it from tax. If it is a separate reward outside the wrapper, check the provider’s tax treatment and the ordinary savings-income rules.

Worked example

Illustrative interest example: suppose a Cash ISA has an illustrative balance of £10,000 and the account produces an illustrative interest payment of £300 during the tax year.

ISA balance after interest: £10,000 + £300 = £10,300.
Interest within the ISA: £300.
Taxable ISA interest reported as ordinary savings income: £0.

The £300 rate and balance are illustrative. The tax point is that ordinary interest inside a valid ISA is covered by the ISA exemption. A separate cash reward paid outside the ISA could have a different treatment and should be checked against its terms.

The example does not mean every provider bonus is interest. The tax answer follows the nature and destination of the payment, so the account terms and statement entry should be checked before assuming that a separately paid reward is tax-free.

Is a Cash ISA bonus taxable?#

Usually not when the “bonus” is actually additional interest credited within the Cash ISA. The ISA wrapper protects ISA interest. If the provider pays a separate reward outside the ISA, the tax treatment can be different. Keep the statement entry and product terms for your records.

Does a promotional ISA rate count as taxable interest?#

If the promotional rate is simply the interest paid by the Cash ISA, it remains covered by the ISA wrapper. The fact that part of the rate is temporary or labelled a bonus does not by itself make the interest taxable.

Does ISA interest use up my Personal Savings Allowance?#

No. The Personal Savings Allowance applies to taxable savings income outside the ISA exemption. Interest earned within an ISA is generally tax-free and does not need to be reported on a tax return. Keep the statement entry and product terms for your records.

What if the ISA provider pays me a separate cash reward?#

Then check where the payment went and what the provider says it represents. A separate payment outside the ISA is not automatically protected just because you hold an ISA with the same provider. Keep the statement entry and product terms for your records.

Will the 2027 Cash ISA limit make my existing ISA interest taxable?#

No. The published 2027 reform reduces the annual Cash ISA subscription limit for under-65s to £12,000; it does not convert existing Cash ISA interest into ordinary taxable bank interest. Keep the statement entry and product terms for your records.

How can I tell whether my ISA bonus is really interest?#

Check the account terms and the statement entry. Look for whether the payment is credited inside the ISA, how it is described and whether the provider treats it as part of the interest rate. Ask the provider for written clarification if it is unclear.

Keep reading

Next question →How is bank interest calculated daily and paid monthly?

Sources

Figures were checked against these sources before publication. If a rule changes, we update the page and show the new date.

General information, not personal financial advice. Rules depend on your circumstances; check the official source or speak to a regulated adviser before acting.