All the leaves are brown and the tax returns are due

The approach of autumn heralds a self-assessment deadline. Melanie Bien shows what to look out for as you fill in the form

It may be the last thing you want to do, as summer gives way to the long autumn nights, but completing your 2003-04 tax return and sending it back to the Inland Revenue by the end of the month will save you time and effort in the long run. It could also reduce stress, as you may be eligible to pay the tax you owe throughout next year - rather than coughing up a one-off lump sum in January.

It may be the last thing you want to do, as summer gives way to the long autumn nights, but completing your 2003-04 tax return and sending it back to the Inland Revenue by the end of the month will save you time and effort in the long run. It could also reduce stress, as you may be eligible to pay the tax you owe throughout next year - rather than coughing up a one-off lump sum in January.

Return your form by 30 Sep- tember and the Revenue will work out the tax you owe, or provide a rebate for what you are due, saving you from complicated calculations. And errors: research from IFA Promotion reveals that miscalculations on self-assessment forms will cost UK taxpayers £296m this year.

You must pay your tax bill by 31 January, or face an automatic £100 fine. However, if you owe less than £2,000, you can choose to pay this through your PAYE code instead. This will enable you to spread your payments throughout 2005, avoiding the stress of remembering the various deadlines during the year. It also means you won't have to fork out a large sum of money straight after Christmas, says the Association of Chartered Certified Accountants.

Even if you owe more than £2,000, so can't spread your payments out, getting your return in now means you will know what you owe and have enough time to plan how to pay for it, advises Jason McLaughlin, tax partner at accountants McLintock & Partners.

Around one in three taxpayers are obliged to complete a self-assessment return. If you are a higher-rate taxpayer, self-employed, have invested money to earn interest or have a new source of untaxed income - such as rental property - you may need to complete a return.

Most taxpayers received their forms in April for the 2003-04 financial year. If you didn't get a form, and think you need one, contact the Revenue now. The deadline will be extended from 30 September to two months after the date on which your return is issued.

If you want the Revenue to work out your tax bill, don't delay. Gather up all the paperwork you need, including your P60 or P11D from your employer, your bank statements and bills, details of investments, and any earnings through self-employment. If any of the information you need is missing, you may just have enough time to obtain replacement copies before the end of the month.

Filling out the form itself shouldn't take longer than an afternoon, unless your tax affairs are extremely complicated. Arm yourself with a calculator and pencil at first (in case you make mistakes) and take care to complete the form fully and correctly. Every year, returns are rejected because of simple errors such as failing to sign the form or ticking boxes only to omit the relevant information.

If you submit your return before 30 September but it's rejected because you've forgotten some information, the Revenue won't guarantee that it will calculate your tax before the 31 January deadline. So double-check before you send off the form.

Make sure you photocopy your return before you send it to the Revenue, and use it to check the taxman's calculations, as mistakes do happen. Any tax you owe will be shown on a Statement of Account, which you should receive in mid-December. This comes with a payslip for you to make any required payment by 31 January next year. If the Revenue owes you money and you have ticked the box asking for a refund, this will be settled according to the method indicated.

Even if you miss the 30 Sep- tember deadline, you may still be able to avoid having to do any calculations. If the Revenue receives and processes your return by 30 December, it will aim to get the tax calculation to you in time for 31 January 2005, although this isn't guaranteed.

But if you have internet access, you can file the return online right up until 31 January and your liability will be calculated automatically. Go to www.inlandrevenue.gov.uk and follow the links. To use this service, you have to apply to the Revenue for a registration number, and this process could take a couple of weeks. In other words, don't leave it until the last week of January before registering.

Remember that 31 January 2005 is the absolute cut-off date for filing your return. By then you must have sent back your form, calculated your liability and paid any tax you owe.