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PARTLY

As of 13 August 2026, AI can only partly calculate your late tax return penalty.

This still needs a person who signs their name to it.

Can you do it?

5 minutesto a draft.

30 minutesto something you’d act on.

Cost, all in£0

Skill neededchat-fluent

Who has to check ityou

What the alternative costsThe supplied tool data does not price a UK accountant or tax adviser for this task.

If this goes wrong: you rely on the wrong penalty, miss an appeal or pay HMRC the wrong amount.

What to actually do

  1. Hand it to a person

    The route this page recommends

    A person who owns the outcome does this end to end, worth it when the failure is dear.

  2. Use a tool built for this

    Second choice

  3. Do it yourself

    The distant third

    A chat interface, chat-fluent skill, and roughly 30 minutes until you can act on the result.

    How to actually do it

    1. Open the relevant late-filing penalty guidance on GOV.UK and your HMRC online account, and copy the current rules and any penalty notice into a document.
    2. Gather the return type, tax year, filing deadline, actual filing date, tax due, payments and payment dates, previous penalties, and details of any reasonable excuse.
    3. Paste those facts and the copied GOV.UK or HMRC guidance into the prompt, replacing each bracketed slot and leaving any unknown item clearly marked as unknown.
    4. Ask the chatbot to produce the rule-based calculation table, showing the arithmetic and separate outcomes for any genuine ambiguity.
    5. Compare each rule, date and figure in the response with the GOV.UK guidance, the penalty notice and your HMRC account, correcting the calculation if any input differs.
    6. If the amount, reasonable excuse or appeal position remains unclear, ask HMRC or a UK accountant or tax adviser before paying or appealing.

    Prompt

    Calculate my possible UK late tax return penalty using only the facts and current GOV.UK or HMRC rules I paste below. Do not invent a rule, date, rate or figure, and do not assume that a reasonable excuse has been accepted. Show every step in a table, including the filing deadline, actual submission date, tax due, payments made, the rule used, and the resulting amount. If the facts are incomplete, list the missing facts instead of guessing. Give separate results for each plausible interpretation where the rules or dates are ambiguous. Clearly label the result as an estimate or rule-based calculation, not an HMRC decision. Facts: [return type] [tax year] [filing deadline] [date filed] [tax due] [payments and dates] [reasonable-excuse details] [previous penalties or appeals]. Current GOV.UK or HMRC guidance: [paste the relevant text or links].

    Open it prefilled in ChatGPT or Claude, or copy it into Gemini, which takes no prefill link.

What it gets wrong

  • AI cannot know whether HMRC will accept your reasonable excuse or change a penalty after an appeal.
  • AI cannot retrieve your HMRC account, penalty notice, filing history or payment record unless you provide the relevant details.
  • AI cannot safely fill gaps in dates, tax due or payments without risking the wrong penalty calculation.
  • AI cannot take responsibility for paying, appealing or disputing the penalty with HMRC.

What caps this at PARTLY: judgement under ambiguity, legal accountability and stakes of error.

How we scored this

Five axes, each scored nought to two by hand: ten means AI carries the task cleanly, and the thresholds that turn a total into YES, PARTLY or NO are published in the methodology. Each axis name links to its definition.

AxisScore (0–2)
Output2
Inputs1
Verification1
Liability1
Effort delta2
Total7 / 10

The methodology and its thresholds are published in full.

FAQ

Can AI calculate my late tax return penalty?
Partly. AI can apply the rules and arithmetic when you provide the exact dates, figures and current GOV.UK guidance, but HMRC decides the penalty and any reasonable-excuse issue. This is not professional advice.
How much is the penalty for filing my tax return late?
There is no reliable single amount without your return type, filing deadline, filing date, tax due, payments and any accepted reasonable excuse. Use the current HMRC notice or GOV.UK rules, then have AI show the arithmetic rather than guess the figure.
Can ChatGPT work out my HMRC late filing penalty?
It can produce a rule-based calculation from facts and guidance that you paste into the chat. It cannot see your HMRC account or decide whether HMRC will accept an appeal, so compare the result with HMRC and ask a UK accountant or tax adviser if the case is disputed.
Can I appeal a late tax return penalty if I had a reasonable excuse?
AI can help organise your timeline and draft a factual explanation from your evidence, but HMRC decides whether the excuse qualifies. This is not professional advice, and a serious or disputed case should go to a UK accountant or tax adviser.

Nearby answers

All Tax returns & HMRC rulings

Assessed by gpt-5.6-luna (gpt-5.6-luna) on 2026-08-13, second-checked by an independent model. Wrong somewhere? Email [email protected] and it gets re-checked.

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