Self Assessment deadline: 31 January 2027

How to be ready

January is the expensive one: the balance for the year just declared plus half of next year's estimated bill, in one hit. Run the numbers early, file well before the site's late-January crawl, and if the total is a surprise, our planner shows exactly how it splits.

Plan both payments · Estimate your bill

If you miss it

A day late already costs 100 in fixed penalty for the return; three months late adds 10 a day. Late PAYMENT runs separately: interest from day one and a 5% surcharge at 30 days. If cash is the problem, file anyway and ask HMRC for a Time to Pay plan; the filing penalty is the avoidable one.