Can I increase my lifespan by killing myself using the Death Note?

Question

Suppose I wrote that I will be killed by a UFO falling from space in the year 2315 while I am lifting.

Will the Note increase my lifespan? In other words, will I still be alive by then?

Answer 1

No. There are some rules that prevent this. From the Rules of the Death Note wiki:

1. The 23-days rule

   How to use: XXVII

   1. [...]
   2. If you write, “die of disease” for the cause of death, but only write a specific time of death without the actual name of disease, the human will die from an adequate disease. But the Death Note can only operate within 23 days (in the human calendar). This is called the 23-day rule.

2. Situation/cause of death is impossible

   How to Use: LIV

   1. [...]
   2. In the occasion where the cause of death is possible but the situation is not, only the cause of death will take effect for that victim. If both the cause and the situation are impossible, that victim will die of heart attack.

   While an UFO falling on your head is technically unlikely, but not impossible, the fact that you'll be naturally alive by 2315 is impossible. You'll just shorten your life, not make it longer.

3. Setting death after original lifespan

   How to Use: LVII

   1. In the Death Note, you cannot set the death date longer than the victim’s original life span. Even if the victim’s death is set in the Death Note beyond his/her original life span, the victim will die before the set time.

Answer 2

No. There is a rule specifically against that:

In the Death Note, you cannot set the death date longer than the victim’s original life span. Even if the victim’s death is set in the Death Note beyond his/her original life span, the victim will die before the set time.

So basically, you'll die of a natural (or whatever your end-of-lifespan-death would be) death before what's written in the Death Note would take effect.

Answer 3

it wouldn't work, because it's beyond your lifespan. but let's say, if you would ask someone with shinigami eyes if he can tell you, your remaining lifespan you could figure out your death date, and then write something like: [your name] dies peacefully at the 3rd may 2087 (just an example). i think this could work because, you still would die on your date of death.