You will normally be sent a National Insurance (NI) number, which looks something like AB123456C, just before your 16th birthday.
You'll only ever be issued with one NI number, and it stays the same for life. It keeps a record of your National Insurance contributions, which over your working life can entitle you to some benefits and a state pension.
It's important to keep safe, like you do with other important personal data. Any new employer you have needs to know it, to pay in your contributions correctly. And you will need it if you want to talk to HMRC about tax and benefits, or when applying for things like a provisional driving licence, ISA savings account or student loan.
But if you've lost your NI number, it's not the end of the world. There are several ways to find it again:
Find it online
You can check your number using your online Personal tax account or on the HMRC App. When you go online you’ll be asked some questions to start with, to confirm who you are. Don’t worry if you can’t get into it on your first attempt, you can try again later. Once you’re in you can view, share or print a copy of your NI number confirmation letter.
Here's a quick HMRC video that shows you how to access it:
Look back through old records
You'll find your NI number on many documents you'll have received from your employer or HMRC. Check old payslips, P60s, or any letters about tax, pensions and benefits.
Request it by post
Complete an online form on the HMRC site and they'll post you your NI number again. There's also a HMRC phone line that can send your number by post if you would rather do that - see the National Insurance Number Helpline for more.
Getting a number sent by post can take up to 15 days though, so don't leave it til the last minute!.
Be alert to scam companies that promise to provide your national insurance number online in return for a fee. Getting your national insurance number is free and it is issued by HMRC.