You can find your lost National Insurance Number by phoning the HMRC. During the phone call you will need to answer all the security questions they ask. If successful your National Insurance Number will arrive in the Post within 3 weeks.
The telephone number to call is 0300 200 3500. If you are outside of the UK you will need to phone +441912037010.
Online Application
Quickest Route to finding your national insurance number
If you have a Government Gateway account you will be able to sign in and print out your National Insurance Number straight away. You can apply for a Government Gateway account if you don’t already have one. This is the quickest way but not always possible so you might have to use one of the below methods.
If you’re trying to find your lost national insurance number, start by checking any official documents where your NIN might be listed, such as your payslips or previous tax returns. Another handy tip is to check the national insurance category letters as these often accompany your NIN details.
In the event you are unable request your National Insurance Number using the above methods you will need to complete form CA5403. Form CA5403 is located on the HMRC website, it is designed to be filled out online and printed. Once complete you will need to sent it to;
National Insurance Number Contributions and empolyers office, HM Revenue and Customs, BX9 1AN
If you require your CA5403 form to be in Welsh then you will need to call 0300 200 1900 and ask for form CA5403W.
- Is there a way to fast track my application?
- Will my lost National Insurance Number stay the same when i request a new one?
- Will the HMRC be able to tell me my National Insurance Number over the phone or email?
- What security questions will i be asked when i phone the HMRC?
- How do i get a Government Gateway account?
- Why didn’t i get sent a National Insurance Number when i was 16?
- What happens if the HMRC never issued me a National Insurance Number?
- Consequences of Not Knowing Your National Insurance Number
Is there a way to fast track my application?
No, there is absolutely no way you can fast track your application. No amount of money would be able to speed up the process. The quickest way is to sign into your online government gateway account and print it straight out. Otherwise its a waiting game of 3-7 weeks.
Will my lost National Insurance Number stay the same when I request a new one?
Yes, your National Insurance Number will never change. Your number is unique to you and won’t be cancelled, even if it is inactive or you leave the country for a period of time.
Will the HMRC be able to tell me my National Insurance Number over the phone or e-mail?
No. The HMRC helpline will only be able to send you your lost National Insurance Number via post for security reasons. They are unable to pass your number over the phone or e-mail.
What security questions will I be asked when I phone the HMRC?
The HMRC will ask a series of security questions in order to discuss your application. These questions may be asked in any order. You will be asked to confirm your full name (you must include any middles names or any other names you may not usually use), date of birth, full UK address including postcode, UK contact telephone number (if you have one) and nationality.
How do I get a Government Gateway account?
You will need to register for an account online at the Gov.uk site. In order to register you must have an active e-mail account in which you are able to access. You will receive an e-mail confirming your account has been fully registered once you have followed all the necessary steps.
Why didn’t I get sent a National Insurance Number when I was 16?
If you have reached 16 years of age and not received a confirmation letter this may be due to a few reasons. You or your parent/guardian may have not informed the relevant government bodies of any address changes. This is the most common reason for not receiving a confirmation letter. If you are not living in the United Kingdom at the time of your 16th birthday, you will not receive a confirmation letter of your national insurance number. Letters are sent via standard Royal mail post, which unfortunately on some occasions is known for letter loss at busy periods such as Christmas holidays.
If you have not attended a UK school or your parents have not claimed any form of benefits relating to yourself you may not be registered on any government system. This being the case you would not receive a National Insurance Number when you reach 16.
What happens if the HMRC never issued me a National Insurance Number?
If you have contacted the relevant departments and they have confirmed you have not been issued a national insurance number, you will need to go through the process of applying for one. When you apply for a new National Insurance number, you will be asked to confirm that you have never been issued a national insurance number previously. Please make sure they understand you have already tried the lost National Insurance Number helpline. Otherwise they will send you around in circles. Please check your payslip or sign into your Government Gateway to see if your National Insurance Number is located there.
Consequences of Not Knowing Your National Insurance Number
If you do not know your National Insurance number, it can potentially impact your tax situation. In situations where your employer is unable to confirm your NI number, they might resort to putting you on emergency tax. This means you may end up paying more tax than necessary until your correct details are received by HMRC.
Emergency tax is a temporary tax code used by HM Revenue and Customs (HMRC) when they don’t have enough information to determine your correct tax code. This often happens for various reasons, including starting a new job, moving jobs, or if you’ve recently been self-employed.
As of 2025, the emergency tax rate in the UK is set at a standard rate of 20%, which is applicable to most taxpayers. This rate can be triggered when individuals do not provide their employers with a valid Tax Code, leading to the deduction of tax at the basic rate instead of the individual’s correct tax rate.
This being the case its very important to find your lost national insurance as quickly as possible to avoid higher rates of tax than necessary.
If you have any questions please leave a comment below, our admin team or our community will be able to help. Please let us know if any of the above information has any inaccuracies by sending an email to admin@nationalinsurancenumber.org.
