The tax system is very complicated in the UK. If you are under 65 years old and your annual income is less than £100,000, you are entitled to basic personal allowance. For 2012-2013, it is £8,105. There fore, the tax code for that will be 810L.

If your age is between 65 and 74, you get a tax code that starts with P, and you are entitled to have tax free allowance £10,500 for 2012-13. If you're over 75, you get a Y code, and a tax free allowance of £10.660.

If you have additional income or receive goverment benefits, the code will be different. It is better to talk to a qualified accountant or contact HMRC directly.