The fine is the smaller problem
Overstaying accrues a daily fine up to a cap, payable at departure or when the situation is regularised. Most people focus on that number. The consequence that actually matters is the re-entry ban: longer overstays trigger bans measured in years when you leave, and those follow you into every future application.
How people end up there
Rarely by choice. The common routes are a refused extension where the applicant did not realise the clock had restarted, a departure without a re-entry permit that quietly voided an extension, a passport renewal that separated the stamps from the new book, and simple misreading of a stamp. None of these look like immigration offences at the time.
If it has already happened
Act on it rather than waiting. The consequences scale with duration, so every additional week narrows the options and worsens the outcome. Whether the right step is a short extension, a change of basis or a planned departure depends on the length of the overstay and the status underneath it — but all of them are better than a further month of hoping.
What prevents it
A calendar rather than a memory. Extension expiry, 90-day reporting windows, re-entry permits before travel and permit renewal dates all live in the same place, with lead time built in. Nearly every overstay we see was preventable a month earlier at no cost at all.