I have overpaid tax in the UK this tax year, and for cash flow reasons, it would be best to get this back as soon as I can by filing a tax return as soon as possible after the year ends. How quickly does the HMRC accept self-assessment tax returns after the end of the tax year?

  • I don't know the answer (but it's a good question) - however, be aware that submitting very early can lead to complications: telegraph.co.uk/finance/personalfinance/tax/11950784/… – Vicky Mar 15 '19 at 17:23
  • Also note that if you haven't done one before you need to register for the system, which requires some info to be sent through the post and therefore can take several days. Make sure you do this in advance of when you need it. Also, you will need some information from your employer (P60, P11D) and bank account interest statements etc. which won't necessarily be available straight away at the end of the tax year, so it's not necessarily just about HMRC's ability to accept the return. My employer doesn't issue P11Ds until July. – Vicky Mar 15 '19 at 17:25
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    Re the telegraph issue, I'm not sure if HMRC actually collect an underpayment for year N in the year N+1 taxcode, rather than year N+2. What may have actually happened in that case was that they adjusted the tax code for year N+1 based on the assumption that things would happen the same as in year N, i.e. to get PAYE for year N+1 more accurate. – GS - Apologise to Monica Mar 15 '19 at 18:23

Checking my records, I have successfully submitted a return on 10th April for the just-finished tax year, and I received the refund (several thousand pounds) on 19th April.

As outlined in this question, you don't need a P60 before you submit if you can infer the figures on it from your final payslip. Likewise you should be able to calculate savings interest yourself from bank statements. If you expect a P11D then you have more of a problem as those are typically not issued for a few months.

HMRC will typically immediately adjust your tax code for future tax years based on the information in a tax return. For example if you claim a certain amount of gift aid, personal pension relief, savings interest and employment expenses, they will assume the next tax year will have the same figures and will issue a tax code designed to get PAYE exactly right the next year.

This may or may not work to your advantage, for example if you make a large one-off pension contribution in year N, they will assume it will happen in future years too and will end up underpaying tax via PAYE for year N+1 and year N+2 until you submit the tax return for year N+1, so you'll end up owing them money - not a problem if you plan for it as it just makes your cashflow better, but you have to be aware of that. In extreme cases if you have a lot of underpaid tax in year N+1/N+2 might even lead to them demanding a payment on account for the following tax year.

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