A post-Christmas treat: file your tax return

Christmas shopping may be the main thing on your to-do list right now. But unless you relish the prospect of spending January in a panic, chasing up paperwork, there's something less exciting you need to pay attention to filing your self-assessment tax return.

First the good news not all of us need bother. If you need to submit a tax return, then HM Revenue & Customs (HMRC) should have notified you by post back in April, and told you how to go about filing a return. You are likely to have to fill in a return if you tick one or more of these boxes: you earn £100,000 or more a year; you are self employed; you have income from property or investments; you are seeking tax relief on large work-related expenses; or you receive child benefit and your income exceeds £50,000 (this last is a new addition for a full list, see here).

If you only earn a salary from an employer (taxed on a pay-as-you-earn basis) and your other tax affairs are simple, you probably haven't been contacted. Although if you've moved recently, make sure that you (or your employer) have given HMRC your current address.

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So what if you do have to file a return? You'll have to file electronically the deadline for paper returns was 31 October, but there's still plenty of time to file online to hit the 31 January 2013 deadline. If you've done it before, you can simply get online with your existing user name and password. However, if you're doing it for the first time, you'll need your ten-digit Unique Taxpayer Reference (phone 0845-900 0444 if you don't have it).

You can then register for online services here. You'll create a password and receive a user ID. Now you need to wait for HMRC to send you an activation code. Once you have that, activate the account within 28 days, and you can start to file online.

To make your life easier, get certain key documents together first. These include your P60 from an employer (or P45 if you left work last year), annual interest statements from banks, and statements relating to dividends paid from investments. Having all this ready makes filling in the return much easier.

Failure to file on time can land you with a £100 fine, plus added charges once you are three months late, so don't put it off, however tedious it may seem.

And if you think you may have failed to pay enough tax (by not declaring income, say) in previous years, the good news is that HMRC is running its first tax amnesty for the general public. Come clean now and you should avoid a hefty fine.