The length of time for which you should buy Term Life Insurance should be proportionate to the amount of time your need exists. If you have a new baby and want to provide for your child if something should happen to you, I would recommend 25 or 30 year Term, to get them through college, and also to cover other children you may have. If you have just gotten a 30 year mortgage, 30 year Term is good for that.
If you do not have a specific need in mind and are getting Term insurance for the price, it is usually a good idea to lock it in for as long as you can afford. If your health would change even a little bit, it can be much more expensive to buy a new Term policy in the future.
The question assumes that your financial liabilities, future obligations, and any philanthropy have a limited time certain horizon. If you’re under age 50 you can secure up to 30 year, a period that coincides with a 30 year mortgage as an example. If you over age 50 the length of term coverage becomes shorter.
If you do not have a specific need in mind and are getting Term insurance for the price, it is usually a good idea to lock it in for as long as you can afford. If your health would change even a little bit, it can be much more expensive to buy a new Term policy in the future.