Self Assessment: what you actually need before 31 January

Every January, the same thing happens. Someone sits down in the last week of the month fully intending to finish their return, gets four screens in, and discovers they cannot find a P60, or a dividend voucher, or the completion statement from a property they sold in June. The return then does not get filed, and a penalty follows that had nothing to do with the tax owed.

The fix is boring and it works: gather the documents first, in one sitting, before you open anything official. Below is the list in roughly the order that people find they are missing something.

Employment and pension income

• Your P60 for the tax year, from every employer you had
• A P45 for any job you left during the year
• Your P11D if you had a company car, medical cover or other benefits
• Pension statements — both what you drew and what you contributed

Pension contributions are the single most commonly missed item on returns prepared by the taxpayer themselves. If you are a higher-rate taxpayer paying into a personal pension, relief above the basic rate is not given automatically — it has to be claimed on the return.

Self-employment

• Total income for the year, and the invoices behind it
• Business expenses, split by category rather than one lump sum
• Details of any equipment bought, for capital allowances
• Bank statements covering the full year, business and any mixed personal account

Property

• Rental statements from your letting agent, or your own rent records
• Mortgage interest statements — interest, not the total payment
• Invoices for repairs, and separately for any improvement work
• Completion statements if you bought or sold during the year

Investments and everything else

• Dividend vouchers or a consolidated tax certificate from your broker
• Bank and building society interest for the year
• Gift Aid donations — these extend your basic rate band and are frequently forgotten
• Child Benefit received, if anyone in the household earns above the charge threshold
• Student loan plan type, if you are repaying

If you are already late

Filing late is better than not filing. Penalties escalate the longer a return is outstanding, and a return that is filed — even late — stops the worst of that escalation. If there is a genuine reason for the delay, there is an appeal process, and it is taken more seriously when the return is already in.

If you have several years outstanding, that is a more common position than most people assume, and there is a defined route through it. It is worth taking, because HMRC treats coming forward voluntarily very differently from being found.