There is no fixed deadline for claiming your State Pension, but it is not usually paid automatically, so you need to apply when you want to start receiving it. You can normally apply up to four months before reaching State Pension age. If you apply after reaching that age, you may be able to request backdating, usually for up to 12 months, although this can affect other benefits or pension choices. Check the latest rules and apply through the official GOV.UK State Pension service.