It's all too tempting to leave 2020/21 tax return completion to the last minute, BUT the reasons for not doing so are multiple:- 1) if you are employed under PAYE you will only be able to have any underpayment arising collected via your tax coding for the year 2024/25 if you submit your tax return by 31st October 2023 for paper returns, or 30th December 2023 for online versions. If you miss this deadline, the full amount of any underpayment will become due for payment on 31st January 2024. Delay could therefore cost you the taxpayer considerably in cash flow terms.2) if your tax return is submitted after 31st October 2023, you will not have the option of completing a paper form - HMRC will only accept an online version. Guard against computer problems by keeping your options early - complete your tax return early to avoid potential problems.3) if your tax return is submitted after 31st October 2023, the onus is on YOU as the taxpayer to calculate your own tax liability and to make any payment on due, regardless of whether you hold a relevant payslip. If your return is submitted before that date ,the onus is on HMRC to calculate your liability and provide any relevant payslip in good time for payment.4)If your return is late, you will be fined a minimum of £100, regardless of whether you have a tax liability or not - the longer the return remains outstanding, the higher the penalty - it could be as much as £1200) the earlier you complete your tax return, the more notice you will have of any liability and the faster you will receive any refund due. There are no advantages to late completion - be smart, be swift.