Nobody knows that, not even Seagate.
A harddrive can die at any point starting from the day you turn it on for the first time. According to a study by Google, it doesn't even matter much how you stress the harddrive.
My rule of thumb is to expect three years of service from a harddrive and anything beyond that is a bonus. But you might get lucky and have the same harddrive work for ten years.
Since you don't know how long a harddrive will last, you need to take this into account by backing up important data regularly, and if you can't accept having to wait for a harddrive replacement if your drive dies, then you need to buy a spare drive you can save until you need it.