UTR Number

A 10-digit number assigned by HMRC to every UK taxpayer, required for filing Self Assessment tax returns and setting up as self-employed.

You cannot file a Self Assessment tax return without a UTR. Registering with HMRC as self-employed automatically generates one, but it takes up to 10 days to arrive, so register early.

You start freelancing in September. You register with HMRC as self-employed. They post your UTR to your registered address within 10 days. You use it to file your tax return by the following 31 January.