Are you wondering if the personal allowance is prorated – i.e you are only given a portion of it if you only work for part of the tax year?
Perhaps you are about to leave the country or maybe you have just left college and only just started work. Perhaps you are checking what happens when someone has died.
In any case the answer is no, the personal allowance is not prorated – everyone is given the full personal allowance to use in one tax year.
For example, if you are in full time education, and you start work in the January of a particular year, then you are still given the whole personal allowance that you can apply to your earnings from January to 5th April. So for 2016/17 you could earn £11,000 and not have to pay any tax on that money.
Or maybe you leave the country half way through the tax year and become non-resident then you are still entitled to use the whole of the personal allowance for the period of the year that you were resident in the UK (there are other complex rules on earnings overseas that may have to be taken into account though).
Or, if someone dies perhaps in May, then their executors can still set their earnings for that tax year against the whole personal allowance for that tax year. They would then need to claim the overpaid tax from HMRC.
One upshot of this, if it is the case that you start or finish earning in the middle of the tax year, is that it is possible that you will pay too much tax as your tax code may assume that your personal allowance should be spread over the whole tax year.
In terms of starting a new job, you may be taxed at the basic rate to start with until your tax code is sorted out.
If you have stopped earning part way through a tax year, you should check how much tax you have paid. If you think you have paid too much tax then you can reclaim this overpayment at the end of the tax year. In some circumstances you may be able to get a refund of over paid tax before the end of the tax year. Check with the tax office if you need clarification.