Do You Need a National Insurance Number for an ISA?

Yes. If you are eligible for a National Insurance number, every new ISA application has to include it, and a provider cannot open the account without it. The rule applies to cash ISAs, stocks and shares ISAs and the rest, and it has been in force for new accounts since 6 April 2025¹.

The reason is straightforward. An ISA is an individual account, opened using your National Insurance number, and it cannot be held in joint names². The number is what ties the tax-free status of the account to you and nobody else.

There is one exception, and it matters if it applies to you. If you are not eligible for a National Insurance number, you do not need one. You confirm that ineligibility to your ISA manager instead, and the account can still be opened³.

Yes: every new ISA must include your National Insurance number

The requirement is not a provider's own preference. The government confirmed that from 6 April 2025, new ISA accounts must contain your National Insurance number unless you are ineligible to have one¹. The regulations require ISA managers to obtain a National Insurance number from all investors who are eligible to have one⁴.

In practice this shows up in the eligibility list of almost every ISA on the market. Yorkshire Building Society states simply that you will need a National Insurance Number to open an ISA⁷. VIDA Bank lists "have a National Insurance number" among its conditions⁸. London Mutual Credit Union goes further: it says it will not be able to open a cash ISA without a National Insurance number or a declaration to confirm you do not hold one⁹. Bank of Scotland, Metro Bank, Saffron Building Society, Hodge, Skipton, Halifax, first direct, M&S Bank, Suffolk Building Society, Nottingham Building Society, HSBC and RBS all set out the same requirement in their own words¹⁰.

The wording varies slightly, and the variation is worth understanding. Some providers say you must provide your number "if eligible to hold one"¹⁶. Others state it flatly as a condition of applying⁸. Both come to the same thing: if you are eligible, the number is required; if you are not, you say so.

If you are not eligible for a National Insurance number

Not everyone who can hold an ISA is eligible for a National Insurance number, and the rules account for that. Investors who are not eligible may subscribe once they have confirmed their ineligibility to their ISA manager³. The legislation sets out that a qualifying individual may only subscribe to an account that is not a junior ISA account if the account manager has been provided with their national insurance information and has no reason to believe they fail the eligibility requirement⁶.

In practice, this is a declaration rather than a blank field. M&S Bank tells applicants that if they are not eligible for a National Insurance number, they must declare this as part of the ISA application¹. HSBC frames it the same way for its stocks and shares ISA: you can provide your National Insurance number or confirm you are not eligible to apply for one¹⁷.

A National Insurance number is normally needed to work or claim benefits²⁹, so people who have never worked or claimed in the UK, including some who have recently arrived, may find themselves in this position. The declaration exists so that the lack of a number does not by itself shut them out of an ISA.

Do you need one for a stocks and shares ISA?

Yes, on the same terms as a cash ISA. Shepherds Friendly lists "have access to your National Insurance number" among the conditions for a stocks and shares ISA³¹. HSBC's guidance says you can provide your number or confirm you are not eligible to apply for one¹⁷.

Providers set it out among the details you need to hand before you start. Fidelity lists your National Insurance number alongside debit card details and bank details for a regular savings plan¹⁸. interactive investor asks for your personal details, including your address history, a debit card to check your identity, and your National Insurance number¹⁹. Vanguard lists it with your name, address, mobile number, date of birth and payment details²⁰. Abundance says simply that it will need your National Insurance number to set up its Innovative Finance ISA²¹.

The pattern is the same across account types: the number is one of the standard pieces of information an ISA application collects, alongside identity and payment details. It is not specific to cash savings.

Where to find your National Insurance number

Your National Insurance number is on your P60, on letters about your tax, pension or benefits, and in the National Insurance section of your personal tax account⁵. It also appears on your National Insurance card, benefit letters and payslips³².

If you cannot find it, you can complete an online form on the HMRC site and it will be posted to you again⁶. If you have never had one, you can apply online for a National Insurance number³³. Once your application is successful, you will receive a letter confirming your number³³.

Some providers point you to the same places. RBS tells applicants to have their National Insurance number ready and notes you will find it on your payslip, P60 or any letters from HMRC²⁸.

What happens if you do not give your number

If you are eligible for a National Insurance number and do not provide it, the account cannot be opened. Saffron Building Society states that it will not be able to open the ISA account if you have not provided your National Insurance Number¹². London Mutual Credit Union says the same⁹. The Tipton requires your National Insurance number to open an ISA³⁷.

This is not a case of an application sitting in a queue. The requirement is a condition of subscribing, not a piece of paperwork to be tidied up later. The legislation is explicit that a qualifying individual may only subscribe if the account manager has been provided with their national insurance information⁶.

There is a second deadline on the horizon. From 6 April 2027, ISA managers must obtain a National Insurance number from all investors who are eligible to have one when receiving a subscription to an ISA⁴. The requirement already applies to new accounts; the 2027 measure extends it to subscriptions more broadly.

Can you open an ISA while you wait for your number?

The account generally cannot be opened until the number is in place, because the provider needs it to complete the application. What you can do is have everything else ready so the application goes through as soon as the number arrives.

Providers give a sense of the timescale once the details are complete. NS&I aims to open its Direct ISA in 7 to 10 working days³⁹. Its Junior ISA follows the same pattern, opening in 7 to 10 working days after identity checks, and it notes this can take longer if it needs to ask for identity documents⁴⁰.

If you are waiting for a number to be issued, the practical sequence is: apply for the National Insurance number, wait for the letter confirming it, then complete the ISA application with the number to hand. If you are not eligible for a number at all, you declare that instead and the application can proceed without one³.

Why the provider needs it

Your National Insurance number is what makes sure your National Insurance contributions and tax are recorded against your name only⁴¹. For an ISA, the number is how the tax-free status of the account is tied to the right person.

The rules require ISA managers to get a National Insurance number on new ISA applications from all investors who are eligible to have one⁴. That is why the field appears on every application form, whether you are opening a cash ISA with a building society or a stocks and shares ISA with an investment platform.

It is worth being clear about what the number is not. It is not a password, and a provider should never ask you to give it in a text message or an email in response to an unexpected contact. If someone contacts you claiming to be from an ISA provider and asks for your National Insurance number, treat it as a scam and contact the provider using a number you have looked up yourself.