What happens if my Delaware LLC misses the 1 June tax?

Delaware adds a US$200 penalty plus interest of 1.5% a month on the tax and penalty. The US$400 annual tax applies to every LLC on the register at any point in the year, with no proration, even if it had no income. Unpaid tax also stops the LLC being in good standing, which banks check.

Source: Annual tax instructions for LLCs, LPs and GPs, Delaware Division of Corporations