It is important that you read the contract that you sign, as this will let you know exactly how long you have to work. If you don’t do this then you risk being sued or receiving a bad reference and, if you end up working notice that you were not expecting, you could find that you are late starting the next job that you have lined up, which could obviously have negative consequences. Usually, the more notice you can give, the better, as this shows that you are being respectful to the fact that the company will have to replace you.