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PARTLY

As of 13 August 2026, AI can only partly calculate your payment on account.

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 costsJulius AI is listed as an AI data analyst that lets you upload a spreadsheet, ask questions and get analysis.

If this goes wrong: you pay too little or too much, and you still have to resolve the difference with HMRC.

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 your HMRC Self Assessment online account and the relevant tax calculation or statement, then note the tax year and copy the figures that relate to the amount due.
    2. Gather records of any payments already made and any changes since the HMRC calculation, such as changed income or an amended return.
    3. Paste those figures into the prompt, keeping the wording and labels from HMRC rather than summarising them from memory.
    4. Ask the chatbot to calculate each payment on account, any balancing payment and the total separately, and to list every assumption or missing figure.
    5. Recalculate the arithmetic yourself with a calculator and compare each result and payment already recorded with your HMRC online account.
    6. Ask an accountant or tax adviser to check the position if the HMRC figures are unclear, your circumstances changed materially, or the chatbot says an exception or reduction may apply.

    Prompt

    I need to calculate my UK Self Assessment payment on account. Use only the figures and facts I provide, do not invent or estimate anything, and ask for missing information before calculating. First identify whether a payment on account appears to apply from the HMRC information supplied. Then calculate each payment on account, any balancing payment shown by the figures, and the total amount due. Keep these separate and show every step of the arithmetic. Do not give tax-planning advice or decide that a relief, exception or reduction applies unless the supplied HMRC calculation explicitly says so. State which figures must be checked against my current HMRC online account and tell me when the result cannot be verified without an accountant or tax adviser. My details are: tax year [insert tax year]; HMRC tax calculation or Self Assessment summary [paste it here]; payments already made [insert amounts and dates]; other HMRC payment-on-account information [paste it here]; relevant changes since that calculation [describe them or write none].

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

What it gets wrong

  • AI cannot access your HMRC account or know whether the figures you pasted are complete and current.
  • AI cannot reliably decide from a short description whether an exception, reduction or unusual tax treatment applies.
  • AI cannot take responsibility for the amount you pay or for errors in your Self Assessment return.
  • A neat calculation can still be wrong if the underlying HMRC tax calculation or payment history is wrong.

What caps this at PARTLY: verification cost, legal accountability and judgement under ambiguity.

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 ChatGPT calculate my payment on account?
Partly. It can calculate the arithmetic from a correct HMRC tax calculation and payment history, but it cannot access your account or confirm that your figures and circumstances are complete. This is not professional advice, so ask an accountant or tax adviser about a serious or unusual case.
What information do I need to calculate my payment on account?
You need the relevant HMRC tax calculation, tax year, payments already made and any information about changes or amendments. Copy the labels and figures from HMRC rather than relying on an estimate or memory.
How do I check my payment on account calculation?
Check the arithmetic with a calculator, then compare the figures and payment history with your HMRC Self Assessment online account. If the result depends on an exception, changed circumstances or an unclear tax calculation, have an accountant or tax adviser check it.
Can I reduce or avoid my payment on account?
AI can explain the information you provide, but it should not decide whether you qualify to reduce or avoid a payment on account. Check the current HMRC guidance and speak to an accountant or tax adviser before making that decision, because you remain responsible for the return and payment.

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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