Companies House penalties are fixed and escalate with time. For a private company, filing accounts one day late attracts a penalty of £150, and the amount rises in steps as the delay lengthens: up to one month late, one to three months, three to six months, and over six months, where the penalty reaches £1,500. If the company has filed late in the previous year as well, the penalties double, so a company that misses two years in a row can face £3,000 for the second late filing alone. Persistent late filing also damages the company's public record.
The official guidance is the best place to check the current rules before you rely on memory. The government page on company filing requirements Companies House filing requirements https://www.gov.uk/running-a-limited-company/company-filing-requirements explains the deadlines, the penalty scale, and the appeal process in plain language. Read it alongside your own company's deadlines, because your accounting reference date determines every date that matters, and a change of year end shifts all of them. If you are unsure of your deadline, check it at Companies House rather than guessing from last year's dates.
Late filing is therefore best treated as a preventable cost, not an occasional misfortune. The penalties are automatic, they escalate quickly, they double for repeat offences, and they sit alongside the reputational damage of a late-filing flag on the public register. A simple system of dated reminders, monthly bookkeeping, and early action when problems arise will keep a micro-entity clear of all of it. If your deadlines are approaching and your records are not yet in order, the sensible move is to get specialist help now, from Micro Entity Accounts https://microentityaccounts.co.uk/