Leveling up and Constitution modifier

[Lost_Nomad]

So I just hit Level four (I feel like I have hair where there was no hair before)
anyway I plan on adding the two points to my Constitution which would move my modifier from +3 to +4.
when I roll my hit dice to get more HP do I use the +3 or the +4?

[Sicarius Victis]

You use the +4.

Not only that, but when your CON mod increases by +1, you als o gain one hit point per level that you already have.

[TundraBuccaneer]

I'm pretty sure you also get the extra hp for previous levels. So adjust your health as if it was +4 from the beginning.

[Lost_Nomad]

Really? thats awesome

[Sicarius Victis]

I'm pretty sure you also get the extra hp for previous levels. So adjust your health as if it was +4 from the beginning.

That's what I was going for with the second part of my comment.

[Lost_Nomad]

That's what I was going for with the second part of my comment.

not that I don't believe y'all but is there a part in the Players Handbook that explains this?

[Sicarius Victis]

If your Constitution modifier changes, your hit point maximum changes as well, as though you had the new modifier from 1st level. For example, if you raise your Constitution score when you reach 4th level and your Constitution modifier increases from +1 to +2, you adjust your hit point maximum as though the modifier had always been +2. So you add 3 hit points for your first 3 levels, and then roll your hit points for 4th level using your new modifier.

Here it is, on page 177.