Self Assessment deadline (31 January)

The Self Assessment return (form SA100) for the tax year ending 5 April is due online by 31 January the following year. The balancing payment and the first payment on account are also due by this date.

What is this filing?

Self Assessment is the UK system for reporting personal income, gains, and tax for self-employed individuals, higher-rate taxpayers, landlords, and others. Paper returns have an earlier 31 October deadline; the 31 January date is for online filing.

When is it due?

Online return and balancing payment: 31 January following the tax year. Paper return: 31 October. First payment on account: 31 January. Second payment on account: 31 July.

What's the penalty for missing it?

Late filing: £100 immediate, £10/day after 3 months (max £900), 5% of unpaid tax or £300 (whichever greater) after 6 months, same again after 12 months. Late payment: interest accrues from 1 February; first 5% surcharge on amounts still unpaid at 3 March (30 days after the 31 Jan deadline); further 5% at 6 months and 12 months.

How PenaltyProof helps

PenaltyProof tracks the 31 January deadline at practice level. Two-track Self Assessment monitoring (primary + secondary dates like 31 July and 5 October) is available on paid plans.

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