If you miss the January filing deadline for the online filing of your tax return, HMRC will charge you an instant £100 penalty.

In some circumstances, this can be reduced provided a valid reason exists for the delay in submission. TaxCalc features a reasonable excuse form, although HMRC find very few reasons acceptable these days.

Penalties can increase substantially until your return is filed and the tax is paid:

• After three months late, a fine of £10 per day is charged up to a 90 day maximum of £900. This is in addition to the £100 penalty, meaning a total penalty of £1,000.
• After six months late, a further fine of either £300 or 5% of the tax due, whichever is the highest, will be charged. This is on top of the penalties above.
• After 12 months late, another £300 or 5% of the tax due, whichever is the highest, will be charged. Again, this is charged on top of the penalties above.

HMRC have the power to charge higher penalties for serious disregard of the filing deadline.