DVSA rules in the UK mean that you can get an MOT test done on your vehicle up to a month, minus a day, before the current MOT validity expires.
As an example, if your MOT expires on October 1st, you can get it tested as early as September 2nd. However, if you get your MOT done early (before it’s actually due), it does not affect or change the expiry date of your new MOT certificate. So, when you get your updated certificate, it will still be valid for 12 months from the original expiry date.
This flexibility on dates allows you to ensure your car meets the required standards without risking any days driving it without a valid MOT certificate. That said, if you get your test done early, before it’s due, it means you will be paying for an MOT test before you legally need to.