The tax year runs from the 6th April - 5th April. Your accounts need to be calculated according to these dates. You can start submitting your tax return on the first day of the next tax year 6th April. 31 October is the deadline for paper filing of tax returns  30 December If you are also employed, you can choose to pay any tax due through your PAYE code, instead of making a big payment on 31 January, but only if you submit your tax return before 30 December. 31 January is the deadline for online self-assessment filing. It is also the deadline for paying any income tax due, Class  4NIC and your first payment on account for next year.  31 July is when your second payment on account becomes due.    Use these shortcuts to download the complete calendar with reminders.   Apple iCal Google Calendar Other   Other Keywords: limit; period; timeframe; when