The self assessment checklist: everything to gather before you file

The January panic is almost never caused by the difficulty of the return. It is caused by not being able to find things. Collect this lot in one sitting and the rest is comparatively easy.

Your identifiers

• Unique Taxpayer Reference (UTR) — ten digits, on any HMRC correspondence
• National Insurance number
• Government Gateway user ID and password, if you file yourself

If you have never filed before, you must register with HMRC first and wait for a UTR to arrive by post. That takes time. Registering in December for a January deadline is how people end up filing late through no fault of their own.

If you are employed as well

• P60 for the tax year
• P45 from any job you left
• P11D for benefits in kind — company car, medical insurance, loans
• Details of any expenses you paid personally and were not reimbursed for

If you are self-employed

• Total sales for the year, and the invoices behind them
• Business bank statements for the full year
• Purchase invoices and receipts, organised by category
• Mileage log or vehicle running costs
• Details of equipment bought — for capital allowances
• Use-of-home figures if you work from home
• Any cash taken out of or put into the business

If you are a landlord

• Rent received per property — agent statements if you use one
• Mortgage interest certificates
• Insurance, ground rent and service charges
• Repairs and maintenance invoices, kept separate from improvements
• Safety certificates, letting agent fees, advertising costs
• Purchase and sale completion statements for anything bought or sold

Everything else

• Bank and building society interest — annual statements
• Dividend vouchers
• Pension contributions, particularly personal ones
• Gift Aid donations
• Student loan plan type and repayments
• Child benefit received, if either partner earns over the charge threshold
• Capital gains — share sales, property disposals, crypto

The five things people most often miss

1. Pension contributions. Higher-rate taxpayers must claim the additional relief through the return. It is not automatic, and it is real money.
2. Gift Aid. Same principle. If you pay higher-rate tax and you donate, you are owed relief you have to ask for.
3. Working from home. Self-employed people routinely under-claim this, either through modesty or uncertainty.
4. Professional subscriptions. Fees to approved professional bodies related to your work are often allowable.
5. Pre-trading expenses. Costs incurred in the seven years before you started trading can often still be claimed in your first year.

Two dates that matter

The online filing deadline and the balancing payment date are both 31 January following the end of the tax year. Registering for self assessment for the first time has an earlier deadline of 5 October. And if your bill is large enough, payments on account fall due in January and July — the single most common cause of a nasty second-year surprise.