21/05/2026
HMRC does not usually chase you before a deadline passes.
The dates are fixed, the system is automated, and penalties are issued whether you remembered or not.
Every year, many business owners end up paying avoidable fines simply because they were unaware of the deadlines or assumed they would receive multiple reminders first.
If you are self-employed, earn rental income, run a limited company, or receive untaxed income, these are important Self Assessment deadlines to know for the 2025/26 tax year.
5 October 2026
If this is your first time filing a Self Assessment tax return, this is the deadline to register with HMRC.
31 October 2026
This is the deadline for paper tax returns. If you miss this date, you will need to submit your return online instead.
31 January 2027
This is the most important deadline for most taxpayers because several things become due on the same day:
• Your online Self Assessment tax return
• Any outstanding tax owed
• Your first payment on account
If you miss this deadline, HMRC automatically issues a £100 late filing penalty, even if you do not owe tax.
The longer the delay continues, the more serious the penalties become:
• After 3 months, additional daily penalties of £10 per day can apply
• After 6 months, HMRC may charge an extra penalty equal to 5% of the tax owed
• Interest and separate late payment penalties may also be added
31 July 2027
Your second payment on account is due by this date.
There is also a major change arriving from April 2026 that many business owners and landlords are still unaware of.
If your qualifying income from self-employment or property exceeds £50,000, Making Tax Digital reporting requirements will apply to you. This means quarterly updates to HMRC will become mandatory rather than filing everything once a year.
Staying organised with your records and planning ahead for these dates can save a significant amount of stress, penalties, and unnecessary financial pressure later on.
General guidance only. Always speak to a qualified professional for advice based on your personal circumstances.