Self Assessment is a system that some people use to report their income and 'capital gains' (profits on the sale of certain assets) to HM Revenue & Customs (HMRC), or to claim tax allowances against their tax bill. It involves completing a paper or online form called a Self Assessment tax return.

How Self Assessment works
Most people pay tax on their earnings or pensions through PAYE (Pay As You Earn). Under PAYE the employer or pension provider deducts tax on behalf of HMRC, and you don't usually get a Self Assessment tax return.

But if you're not on PAYE, and/or are due to pay additional tax because of other income not taxed through PAYE (for example from property or investments above a certain amount, or because you're self-employed) you have to account for this income through Self Assessment. HMRC uses the figures you supply on the tax return to work out your tax bill, or you can work it out yourself.

It's called 'Self Assessment' because you're responsible for making sure the details you provide are right.

Who gets a tax return and when?
Tax returns are usually sent out in early April, following the end of the tax year to which they apply. (A tax year runs from 6 April to 5 April.)

They may also go out at other times, for example, if you want to claim an allowance or repayment or you want to register for Self Assessment for the first time.

Registering for Self Assessment:
If you don't receive a Self Assessment return but think you should, or your circumstances change, phone your Tax Office as soon as possible.

The two types of tax return:-
If you have simple tax affairs including, employees, pensioners and the self employed with turnover less than £15,000, you'll receive the short four-page return.

If your affairs are more complicated you'll receive the full return. This has twelve core pages and extra pages you may need to complete, depending on what sorts of income you get.

If you receive a return you must fill it in and send it back by the deadline even if you don't think you need one.