Key Self Assessment deadlines
Having the support of a qualified chartered accountant and taxation technician will help keep your affairs on the right track and you should not miss any deadlines when you are following their guidance.

Key Date for Completing and Sending Back Your Tax Return
31 October 2009
If you wish to submit a Tax Return on paper.
31 January 2010
If you will complete a Tax Return via on-line submission.

Don't lose sight of 31 January payment deadline!
31 January 2010 is also the deadline to pay your final amount of tax for 2008/09 and, in many cases, make a first payment on account for 2009/10.

Again, having the support of a qualified chartered accountant and taxation technician will help keep your affairs on the right track.

At this stage you may find it difficult to calculate the tax you owe accurately (even with the tax calculation guide supplied!) so this is another time for estimating.

You may decide to be generous in your guesstimate - overpayments will come back to you in due course.

If you do this it is important to complete the details under question 19, which tells HMRC how you would like any over payment refunded to you.

Is the deadline really 31 January?
Tax returns need to be received by HMRC by 31 January to avoid the late filing penalty, but in practice this means if the return is in HMRC's letterbox when they open for business first thing on 1 February, you will have met the deadline.

It is possible to hand deliver your return to a local HMRC office, though you won't get a receipt for your return nowadays - so you may need to think about how to prove your delivery in case there is a subsequent dispute. Delivery by your accountant is an effective proof since he will receive confirmation for his batch of submissions.

Recent BBC news story regarding the January deadline.

HMRC key dates page

OTHER DEADLINES

Reporting new income and gains:
You only have six months from when the tax year ends to report any new income or liable capital gains.

If you become self-employed
You have three months after the calendar month in which you began self-employed work to let HMRC know.

There are key deadlines for filing (sending in) completed tax returns and paying the tax due. If you miss the filing deadline you'll have to pay a penalty. You'll also have to pay interest, and sometimes an extra surcharge if you don't pay tax that's due on time.

If you file your tax return online the deadlines are more generous if you don't want to calculate the tax due yourself. It'll also be dealt with faster and you'll get any repayments due sooner.

HMRC has 12 months from the filing deadline to check and make enquiries about your return. Some of these checks are random, while others may be triggered because figures need further explanation.

They can also correct any obvious errors within nine months of receiving your return. They'll usually let you know on your tax calculation, but in some cases may call to clarify a point. You can ask for a review of any such changes within 30 days.