The Self Assessment countdown: an AI chasing plan for practices

Last checked: 16 October 2026

"Every January it's the same: half my clients send their paperwork in the last fortnight."

This plan runs from mid-October to the 31 January deadline. AI does the repetitive writing (chasers, explainers, payment reminders), and you keep control of the facts and the figures. All the prompts use placeholders. Never paste a client's UTR, National Insurance number or bank details into an AI tool.

The dates that drive the plan

All for the 2025 to 2026 tax year (6 April 2025 to 5 April 2026):

• 31 October 2026: paper returns must reach HMRC by 11:59pm.
• 30 December 2026: last date to submit online if the client wants to pay through their tax code.
• 31 January 2027: online returns must be submitted, and the tax paid, by 11:59pm.
• Source: GOV.UK, Self Assessment deadlines, https://www.gov.uk/self-assessment-tax-returns/deadlines (checked 16 October 2026, 05:39 BST).

Payments on account are due by midnight on 31 January and 31 July. Each is usually half of the previous year's tax. They aren't needed if last year's tax bill was under £1,000, or if more than 80% of the tax was paid outside Self Assessment, for example through a tax code (https://www.gov.uk/understand-self-assessment-bill/payments-on-account, checked 16 October 2026, 05:39 BST).

Week by week

Mid-October: sort the list

• Split clients into three groups: all records in · some records missing · nothing yet.
• Flag anyone filing on paper, because 31 October is close.
• Check authorisations for new clients. For Self Assessment, GOV.UK lists Online Agent Authorisation as the online route and form 64-8 as the paper route. Agents shouldn't use a client's HMRC sign-in details or access their online tax account. If a client is digitally excluded, give them the authorisation request link and a number for HMRC, which will pass them to its Extra Support Team (https://www.gov.uk/guidance/how-to-get-authorised-to-act-as-a-tax-agent-on-behalf-of-your-clients, page updated 7 October 2026, checked 16 October 2026, 05:39 BST).

1 November: first chaser

Send email 1 of the chasing sequence to every client in the "missing" and "nothing yet" groups. The full 3-email prompt is on our client records page: /use-cases/client-records-chasing.

8 and 15 November: follow-ups

Send emails 2 (offer a 10-minute call) and 3 (firm, with your internal cut-off date). Set your own cut-off well before January, e.g. 1 December.

Late November: the "what's still missing" list

[Copy] button on this block (required).

Here is a list of what each client has and hasn't sent, using client codes only (no names or tax references).
For each client, write a one-line status and the single next action. Group them: ready to prepare / waiting on one item / waiting on several items / no response.
List: [paste, e.g. "C014 – bank statements Apr–Jun missing; receipts received"]

Worked example (dummy data, example output): "C014 – waiting on one item: bank statements April–June. Next action: call on Tuesday." "C027 – no response to 3 emails. Next action: phone, then letter."

December: prepare, approve, and explain the bill

Prepare returns for the "ready" group first. When you send a return for approval, explain the January payment in plain English: [Copy] button on this block (required).

Write a short, friendly email to [CLIENT_FIRST_NAME] explaining what they need to pay by 31 January 2027 and why.
Figures: tax for 2025 to 2026 £[x]; payments on account already made £[y]; first payment on account for 2026 to 2027 £[z]; second payment on account £[z] due 31 July 2027.
Explain "balancing payment" and "payment on account" in plain words. British English, under 150 words. Don't change or recalculate my figures. If they don't add up, say so.

Worked example (dummy data, example output). A client's tax for 2025 to 2026 is £4,200. They made two payments on account of £1,800 (£3,600 in total).

This follows GOV.UK's worked example for payments on account (link above). Each payment is "usually" half the previous year's tax, so always use the figures on the client's HMRC statement.

Check every number before you send: the balancing payment, both payments on account and the total. Make sure the dates are right too.

Clients who want to pay through their tax code need their return submitted online by 30 December 2026.

Early January: final push

• Re-run the "what's still missing" prompt.
• For anyone still outstanding, send a final chaser with the penalty facts, below. Quote the GOV.UK figures, not the AI's version.

31 January 2027: deadline

Returns submitted and tax paid by 11:59pm.

The penalty facts to quote

Late filing: an initial £100. After 3 months, £10 a day, up to a maximum of £900. After 6 months, 5% of the tax due or £300, whichever is greater. After 12 months, another 5% or £300, whichever is greater. Late payment: 5% of the unpaid tax at 30 days, 6 months and 12 months, plus interest (https://www.gov.uk/self-assessment-tax-returns/penalties, checked 16 October 2026, 05:39 BST).

After the deadline: records

Self-employed clients must keep records for at least 5 years after the 31 January submission deadline of the relevant tax year. Returns sent more than 4 years after the deadline need records kept for 15 months after sending (https://www.gov.uk/self-employed-records/how-long-to-keep-your-records, checked 16 October 2026, 05:39 BST).

Next steps

• The full 3-email chasing sequence and a new-client onboarding prompt: /use-cases/client-records-chasing
• Help clients keep tidier books next year: /use-cases/bookkeeping
• The latest tool prices and checks: /updates

Prices

The prompts work on the free plans of ChatGPT and Claude. ChatGPT: free plan; Go £6.99/month; Plus £19.99/month. Claude: free plan; Pro £20/month or £199.99/year. Both are UK App Store in-app prices (web prices may differ), from the StackSmart directory, checked 16 October 2026.

Last checked: 16 October 2026.