The tax return filing deadline is 31 January each year where the return is filed electronically. Use this self-assessment tax return checklist to avoid problems with HMRC, or not paying the right amount of tax.

Points to check Practical matters
Include all income sources It’s easy to miss off a bank account or dividends from shares etc. on your return, especially if you’re up against the deadline and have several sources of income. Income tends to stay at a similar level year on year, so check the figures against the previous year’s. If there is a difference in any particular area, do some investigating to make sure you’ve picked everything up.
Check capital gains If you dispose of assets for more than you paid for them, you may need to report the details on the capital gains supplementary pages. However, you can ignore this if your total gains don’t exceed the annual exemption for the tax year, and the proceeds don’t exceed four times the annual exemption. If you are selling a property that has been your only or main residence, check the occupancy history. If it was your main residence for only part of the ownership period, the private residence relief exemption might only apply to part of the gain.
Report losses If you dispose of assets for less than you sold them a loss arises and no tax is due. You might be tempted to ignore these and not report them. However, if you don’t then you won’t be able to use them to reduce future gains, so always report losses.
Pension contributions You need to report any pension contributions other than those deducted by an employer from your gross pay. Doing so will ensure you receive the full tax relief but watch out! If your total contributions exceed £40,000 in a tax year, you might be liable to the annual allowance charge. If your contributions do exceed £40,000, check your contributions for the previous three years, as you can carry any unused allowance forward.
Charitable donations Donations made to registered charities mean tax relief for higher and additional rate taxpayers. Check your bank statements to ensure you pick everything up. Memberships to organisations like the National Trust or English Heritage count as donations if you’ve gift aided them, as well as one-off entry fees into various zoos, museums and exhibitions around the country.
State pension A common misconception is that the state pension is exempt from tax. This is false, though it isn’t taxed at source. Don’t forget to include the amount you receive if applicable.
Higher income child benefit charge If you (or your partner) are in receipt of child benefit and either of your incomes exceeds £50,000, you will be subject to the charge. Don’t forget to include the relevant details.
Marriage allowance If you are a basic rate taxpayer, and your partner does not fully use their personal allowance, they can elect to transfer up to 10% of it to you. This can reduce your tax bill.
Payments on account By default, you will be required to make payments on account for the next year’s tax liability. These are calculated at 50% of the previous year’s tax bill and the first of them is payable on 31 January before the tax year starts, i.e. on the same date as the balancing payment for the return you are filing. Payments on account are only due if your tax not collected at source exceeds both £1,000 and 20% of your total tax liability for the year. However, you can claim to reduce them if you know your income will reduce, or if your tax owing at the end of the year will be less next time. Use caution though, if you reduce them too far you will be charged late payment interest. Read more here
Filing Check that the return files successfully. You should receive a confirmation reference.
Coding out If you want HMRC to collect your tax due via a future PAYE code, you need to have your return filed by 30 December. The amount owing cannot exceed £3,000.
Other tax reliefs Ensure you have claimed any trading or capital losses available from earlier years. If you have made investments under the EIS, VCT or SEIS then you can claim the income tax relief as long as you have been issued with the certificate saying you can do so.

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