Cash ISA FAQs

A Cash ISA (Individual Savings Account) is a savings account that allows you to earn interest on your money tax-free, meaning you don’t pay income tax on the interest you earn.

The main difference is tax treatment. Interest earned in a Cash ISA is tax-free, while interest on a standard savings account may count towards your personal savings allowance.

The Prosper Cash ISA uses the same easy access savings product as the Prosper Simple Saver, which is powered by Griffin Bank Limited and tracks the Bank of England base rate. The difference is that, within the ISA, any interest you earn is not subject to tax.

To open a Prosper Cash ISA, you must:

Yes. Money in your Prosper Cash ISA is held with Griffin Bank Ltd (Firm Reference Number 970920) and is eligible for protection under the Financial Services Compensation Scheme (FSCS).

FSCS protection covers up to £120,000 per person, per authorised bank. Remember, if you have other deposits with the same bank or group, the protection applies to all eligible deposits up to £120,000.

For example, this limit applies across all eligible accounts you hold with Griffin Bank Ltd, including your Cash ISA, Prosper wallet and any other savings you may have with Griffin Bank.

Prosper is approved by HM Revenue & Customs to manage your Cash ISA in line with the ISA Regulations (Reference Number 11923629), while your deposits are held securely with our custodian partner, Griffin Bank Ltd. Griffin is authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and Prudential Regulation Authority (Firm Reference Number 970920).

A flexible ISA lets you withdraw money and put it back without using more of your ISA allowance.
You can only replace up to the amount you withdrew, and only before the tax year ends.

A Cash ISA works like a traditional savings account. Your money earns interest and is protected from losses. It is suitable for short-term savings (1–2 years).

In a Stocks & Shares ISA, your money is invested in the stock market, giving it the potential to grow more significantly over the long term (typically 5+ years). However, the value of your investments can go down as well as up.

The annual ISA allowance for the current tax year is £20,000. The tax year runs from 6 April to 5 April. You can split this allowance across different types of ISAs (Cash, Stocks & Shares…) but the total combined contributions across all your accounts with Prosper or other providers must not exceed £20,000 per tax year.

Yes. You can have multiple ISAs (Cash, Stocks & Shares…) inside and outside Prosper at once, as long as the total combined contributions across all your accounts with Prosper or other providers doesn’t exceed £20,000 per tax year.

For example, if you invest £15,000 in a Stocks & Shares ISA, you’ll have £5,000 remaining to allocate to your Cash ISA (or another ISA) in that same year.

Bear in mind that from April 2027, the Cash ISA allowance will be capped to £12,000 for under-65s, while the Stocks & Shares ISA allowance stays £20,000. Regardless of age, the overall annual ISA contribution limit will remain at £20,000 so you can continue to contribute £20,000 across different ISAs each tax year.

Yes. The minimum balance is £1 for the standard (unboosted) product and £10,000 for the boosted product. The latter is available to new customers only or to existing customers where eligible under specific promotional campaign terms (if Prosper chooses to run a campaign at its discretion).

If you accidentally pay in more than £20,000 across your ISAs in a single tax year, this is known as an over-subscription. HMRC may contact you after the end of the tax year once it has received subscription information from providers. You should contact Prosper before taking any action, as withdrawing the excess funds yourself without guidance may complicate the correction process.

Cash ISA transfers into Prosper aren’t supported just yet, but will be available in the future. Once available, you will be able to transfer a Cash ISA by requesting an official transfer. Do not withdraw the money yourself or you may lose the tax-free wrapper.

You can transfer your ISA out of Prosper at any time. To do this, submit a transfer request with your new ISA provider and they will contact us to arrange the transfer.

We currently only support full transfers.

Transfers typically take up to 15 business days if you’re moving funds to another Cash ISA, or up to 30 calendar days if you’re transferring to a different type of ISA.

No. The Prosper Cash ISA is a flexible ISA. This means you can withdraw money and put it back in within the same tax year without using up more of your ISA allowance. You can only replace up to the amount you withdrew and it must be done before the tax year ends.

It depends on the direction of the transfer, when the money was contributed and whether it is replaced within the same tax year.

From Cash ISA to Stocks & Shares ISA: Yes. For current tax year contributions, you can move money yourself, but only if it’s replaced within the same tax year. Because the Prosper Cash ISA is flexible, if you withdraw money you contributed this year back to your Prosper wallet, your used ISA allowance is effectively reduced by that amount. If you then pay that same amount into your Stocks & Shares ISA before the end of the same tax year (5 April), it will not use up any additional ISA allowance. The net result is that you have moved this year’s ISA allowance from your Cash ISA to your Stocks & Shares ISA without exceeding your £20,000 annual limit.

If you want to transfer money contributed in previous tax years, this is also supported, but a transfer must be requested through our support team. Without following the formal transfer process, withdrawing and paying it into a Stocks & Shares ISA would count as a new contribution and use your current year’s allowance.

From Stocks & Shares ISA to Cash ISA: No. We do not currently support transfers into a Prosper Cash ISA. If you withdraw money from your Stocks & Shares ISA to pay into your Cash ISA, it will count as a new contribution and use up more of your annual allowance. If you wish to transfer money from your Stocks & Shares ISA to a different ISA account, please request a transfer out.

No. You benefit from unlimited withdrawals with a Prosper Cash ISA. You can access your cash within one working day with no limits or penalties.

Your standard interest is calculated daily and paid into your Cash ISA tax-free on the first of each month.

If you have a boosted rate, the extra amount is handled differently. It is paid as a lump sum to your nominated bank account after 12 months or if you close your account.

Because this payment is classified as a cashback reward rather than savings interest, it is not currently considered taxable income by HMRC. If you choose to add your Boost payment into your ISA, it will count towards your £20,000 annual ISA allowance.

Yes. The interest rate can change at any time. However, your Cash ISA is designed to track the Bank of England base rate, ensuring you get a fair return that moves with the market.

No. Your Cash ISA is free to open and use. It is a specific savings account designed to pay you interest.

We retain the interest on uninvested cash in your investment accounts, as well as balances in the Prosper wallet. We do this unapologetically because it aligns our incentives with yours. We want your money invested and growing, not sitting idle.

We also charge for access to private market funds and take a share of the fees you pay for financial guidance. As we grow, we’ll continue to introduce new services with fair pricing, but the core experience stays low-cost and clear.

You can fund your account by moving funds from your Prosper wallet.

Yes. Statements will be provided to help you track your savings, though you do not need to declare ISA interest on your tax return.

All statements and documents are available in the Documents section of your Prosper app.

If you move abroad, you can keep your existing ISA open and continue to receive tax-free interest, but you generally cannot pay any new money into it after the tax year in which you move (unless you are a Crown employee).

No. ISAs are personal savings accounts, so contributions must generally come from your own funds (e.g., from your personal bank account).