Your Unique Taxpayer Reference (UTR) identifies your tax records at HMRC. The number is also known as your taxpayer number or tax reference number and should be used whenever you contact HMRC, or when you file your tax returns. The UTR is a unique 10 digit code. You are automatically given a UTR when you set yourself up to file Self Assessment tax returns or form a limited company. If you have mislaid your UTR, you should be able to find the number on previous tax returns and other documents from HMRC, for example, on notices to file a return and payment reminders. You can also find your UTR in your HMRC online account. If you are still unable to locate your UTR you can call the Self Assessment helpline to request your UTR on 0300 200 3310. The lines are usually open from Monday to Friday: 8am to 8pm, Saturday: 8am to 4pm and Sunday: 9am to 5pm. If you have mislaid your Corporation Tax UTR, this can be requested online and HMRC will send a copy of the number by post to the company’s registered address.