One month and seven days after the end of your VAT period, for both the return and the payment. So a quarter ending 31 March is due by 7 May. Most businesses file quarterly on a stagger HMRC allocates at registration, and you can ask to change the stagger to align with your year end, which is worth doing. If you pay by direct debit, HMRC collects three working days after the deadline, which quietly buys you a little more time. The annual accounting scheme replaces this with one return a year and interim payments on account, which suits businesses with steady turnover and poor appetite for quarterly admin. Filing and payment penalties are separate, and paying late is the more expensive of the two.