I keep getting different information when it comes to pot odds and when it’s +EV play. For example, I’ve been told if you are getting 2-1 odds you need 33% equity for it to be +EV and 3-1 you need 25% and 4-1 you need 20%. Is this correct? The reason it’s been confusing is that Ive also been told if you are getting 3-1 on a call then you need to be right 33% for it to be profitable call? These might be different concepts but I’m trying to understand the difference between them and how to calculate pot odds correctly

You can always convert odds to percentages by adding the 2 numbers together and then dividing by that number.

A simple example:

Assumimg a peefectly fair coin and ignoring environmental factors, the odds of fliping heads or tails is 1:1 (that is both occur with the same frequence). What is the probability you flip heads or tails?

Well 1+1 = 2. 1/2 = .5 so the probability you flip a head or a tail is .5 (or converted to percentages .5×100 = 50%).

The same can be applied to any odds:

2 to 1 ; 2+1 = 3 ; 2/3 = .66 ; 1/3 = .33 (missing extra .01 from repeating decimals)

3 to 1; 3+1 =4 ; 3/4 = .75 ; 1/4 = .25

4 to 1; 4+1 = 5; 4/5 = .80 ; 1/4 = .2

3 to 2; 3+2 = 5 ; 3/5 = .6 ; 2/5 = .4

16 to 21; 16+21 = 37; 16/37 = .432; 21/37 = .567

Normally when talking about pot odds we only care about the "to x" term because that's how much money (ignoring rake) it"s going to cost you to continue so you want to make sure you can make at least that much back out.

You’ve been told wrong.

3 to 1 pot odds means the win amount if you win is 3 and the amount you risk, the call amount, is 1. Therefore, after you call, the total pot is 3+1=4 and you have contributed ¼ of that.

Your “fair” share of the total pot is ¼ and that is the needed win probability to break-even so that EV=0. If your equity is less than that, then EV is negative.

After you get odds and % straightened out, these numbers are for break even. In theory you should make $0 and lose $0 when you make such plays. In my experience, it's better to focus on situations when you're equity and odds are significantly in your favor. Rather than focusing on such marginal spots.