The Self Assessment checklist: records, deadlines and payments on account

January stress is not caused by the tax return. It is caused by the eleven months of records that were never kept, all falling due at once. The return itself — for most self-employed people — is an evening's work when the paperwork is complete, and a fortnight of archaeology when it is not.

This checklist is the complete-paperwork version. Work through it in November and January becomes boring, which is the goal.

First, the admin that must already exist

• Registration. If you started self-employment (or otherwise came into Self Assessment) during a tax year, you must register with HMRC by 5 October after that tax year ends. The tax year runs from 6 April to 5 April.
• Your UTR — the ten-digit Unique Taxpayer Reference HMRC issued when you registered. Everything files against it.
• Your Government Gateway login. Test it now, in daylight, in November. Recovering lost credentials in the last week of January is a queue you do not want to join.
• Last year's return, if you filed one — the fastest way to spot what you are forgetting this year.

The deadlines that matter

• 31 October — deadline for paper returns for the tax year just ended.
• 31 January — deadline for online returns, and for paying what you owe. This is the date that matters for most people.
• 31 January and 31 July — payments on account, if they apply to you (explained below).

File late and the penalty starts at £100 immediately — even if you owe no tax — and grows the longer the delay; pay late and interest runs on the balance. Neither is ever worth it: if cash is the problem, file on time anyway and talk to HMRC about a payment plan.

The records to gather

Business income

• Sales invoices and records of all money in, including cash and platform sales (marketplaces and gig platforms now report seller income to HMRC directly, so completeness matters).
• Bank statements for the year — the backbone every other record hangs off.
• CIS payment and deduction statements, if you subcontract in construction.

Business expenses

• Receipts for everything you intend to claim, organised by category: materials, travel, phone and broadband share, insurance, professional fees, subscriptions.
• Your mileage log, if you claim the flat rate per business mile.
• Your use-of-home working, whether flat rate hours or an apportionment of bills.
• Details of equipment bought in the year, for capital allowances or cash-basis expensing.

Everything that is not the business

• P60 or P45 (and P11D for benefits) from any employment in the year.
• Bank and building society interest, and dividend statements.
• Rental income and expenses, if you let property.
• Pension contributions made personally — these can extend your basic-rate band, so they reduce tax; do not forget them.
• Gift Aid donations — same reason.
• Student loan plan type, and whether you or your partner received Child Benefit while one of you earned above the High Income Child Benefit Charge threshold (check the current figure on GOV.UK).

Payments on account, explained properly

Payments on account are the part of Self Assessment nobody warns you about, and they arrive precisely when a business is young and cash-fragile.

The rule: if your Self Assessment bill is over £1,000, and less than 80% of your tax is collected at source (through PAYE, say), HMRC asks you to pay next year's tax in advance — two instalments, each half of this year's bill, due 31 January and 31 July.

The consequence, in your first year over the line: on 31 January you pay this year's bill plus the first instalment toward next year — one and a half times the bill you were braced for — with another half-bill following in July. It is not extra tax, just tax paid earlier; but as a cash-flow event it deserves to be planned for, not discovered.

If you know your income is falling, you can apply to reduce your payments on account — honestly. Reduce them below what the year finally justifies and HMRC charges interest on the shortfall, so estimate with care.

The case for filing early

Filing in May instead of January changes nothing about when you must pay — the 31 January deadline stands either way — but it changes everything about how the winter feels. You learn the bill months in advance and can save toward it; refunds (CIS subcontractors especially) arrive months sooner; and if something is missing, you find out while there is ample time to fix it. Early filing is the single cheapest stress reduction available in self-employment.

Afterwards

Keep the records behind your return for at least five years after the 31 January deadline — HMRC can ask, and "the receipts are gone" is not a defence. Digitally stored records satisfy this comfortably and take no cupboard space.

And note the direction of travel: from April 2026, Making Tax Digital brings quarterly digital updates for sole traders and landlords with gross income over £50,000 (over £30,000 from April 2027). The January-cramming model of self-employment admin is being retired whether we mourn it or not. The businesses that will not notice the change are the ones whose records are already continuous.

Continuous is what we do. Receipts, invoices and statements flow in all year, every entry is drafted and checked as it lands — AI drafts. AgentLedger validates. People approve. — and your return is assembled from books that were never allowed to fall behind. If you would rather never do January archaeology again, Ask for Details.