Martin Lewis urges action before January Self Assessment deadline to avoid £100 fine

Martin Lewis warned that about 5.65 million people had yet to file Self Assessment returns as of 5 January 2026, and the online filing deadline is 11:59pm on 31 January; missing it carries an initial £100 penalty.

Martin Lewis has urged people with Self Assessment obligations to act before the January deadline rather than leave tasks until the last minute. HMRC figures reported that around 5.65 million people still needed to submit returns for the 2024–25 tax year as of 5 January 2026. The online filing deadline is 11:59pm on 31 January. Mr Lewis noted that late filing and late payment bring financial charges and make resolving issues harder as services become busier. Key facts: - About 5.65 million people had not submitted Self Assessment returns as of 5 January 2026, according to HMRC figures. - The online filing deadline for the 2024–25 tax year is 11:59pm on 31 January 2026. - Missing the filing deadline triggers an initial £100 penalty; further penalties can include daily fines after three months and additional charges at six and 12 months, with separate late payment penalties and interest applied. - Mr Lewis highlighted that interest on unpaid tax is reported at 7.75% and said paying an estimated amount may reduce later charges. Summary: Missing the deadline leads to immediate and escalating penalties and interest, and HMRC contact lines and accountants are reported to be busier as the cutoff approaches. The filing deadline is 11:59pm on 31 January; undetermined at this time.