Any tax you owe based on your Self Assessment return must be paid by 31 January following the end of the tax year. So for the 2025/26 tax year, payment is due by 31 January 2027. If you also make payments on account (advance payments towards next year’s tax bill), the first payment is due on 31 January and the second is due on 31 July. If you miss the payment deadline, HMRC will charge interest from the day after the deadline. After 30 days, a 5% surcharge is added to any unpaid tax, and further surcharges apply at 6 and 12 months. If you cannot pay on time, it is best to contact HMRC early to discuss a payment plan.
