Postby JRG » Thu Jul 03, 2014 8:24 pm
The tax code doesn't prevent tax being deducted, it determines the amount of tax to be deducted. Your taxable income (i.e. the amount you pay tax on) is calculated by deducting your personal allowance from your annual income.
If your annual income is £10,000 and your tax code is 1000L (i.e. your Personal Allowance is £10,000) then your taxable income is £0, so your tax would be £0 x 20% = £0.
If your annual income is £15,000 and your tax code is 1000L (i.e. your Personal Allowance is £10,000) then your taxable income is £5,000, so your tax would be £5,000 x 20% = £1,000.
If your annual income is £20,000 and your tax code is 1000L (i.e. your Personal Allowance is £10,000) then your taxable income is £10,000, so your tax would be £10,000 x 20% = £2,000.
Simples!