In April 2014 the tax allowance for an individual when up to £10,000 per year. This means that you can earn up to that amount every year without having to pay any tax. Anything you earn over the £10k you will be taxed a percentage of. If you are unsure as to whether your tax is correct there are a few simply checks you can make. Check the tax code on your wage slip, for the majority of this it is 100L unless you are receiving benefits in kind. There are also many free salary calculators out there that will work out your Tax and NI off your salary.
When it comes to self employed, the tax allowance for an individual is the same amount, ten thousand pounds per annum. This figure is based on the profit you make in the year, not the turnover. Many self employed people do not pay tax in the first year as this is when they are building up the business. With self employment you are also allowed to deduct any business expenses from your turnover thus reducing the profit you are making.