364T is unusual - I would expect there to be another source of income there. Two jobs? Trust income?

Assuming 364T is correct you have 3645/12 as a tax free allowance a month = £303 tax free a month.

Everything over £303 will be taxed at 20%.

I'm not sure that that was the answer you wanted - you should have received a "notice of coding" showing how your code was made up - if not get the phone number from hmrc.gov.uk and call in and ask how your code was worked out/

Yor tax code should be 810L if thats your only income. You tax code means you will not be taxed until you earn £3645. phone hmrc to sort it out.

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