I know there's been a ton of threads posted like this, but I just don't understand how to do it on my own. I was hoping you guys could help explain it to me.

Okay so sample hand. 1/3 NL Live

3 limpers, we pick up 99 in the CO and limp. SB completes and BB checks.

Flop-10 Q 7 Pot-$15

Everyone checks flop.

Turn-9 Pot-$15

SB bets $24, we raise to $75, he shoves $34 more over and we call.

So the pot is at $233 and our equity is at 22.73%.

What would our expected loss be on this hand?

I think I'm misunderstanding the way to calculate it because if I multiply $233 by 77.27% (KJ hand) it's $180.04 and then multiply $233 by 22.73% (99 hand) it's $52.96. Now if I subtract them I get a negative EV/loss on the hand of $127.08.

I've only put $112 into the pot, so shouldn't my EV loss on the hand be something under $112?

Ah, I forgot to say that Villain has KJo for the straight

Assuming your math is correct you have put in 112 and will get 52.96 back for a loss of 59.04.

Fellow newbie here, sorry to hijack this thread but is that level of maths really important in poker?

Its blown my mind just looking at it :/

Hey thanks for the reply, can you show me exactly how you got that?

At any balanced point of the hand, ie, when you face no bet, you 'own' the amount of the pot that an equity calculator gives you for your hand against your perceived range of the villain's hand.

At the turn the pot starts as $15, the SB bets you raise to $75 and the SB comes in for another $34 on top. At this point you have to call $34 to stay in the hand and realize your equity, the question is should you? If you fold to any bet the EV of this is $0.00.
If you do call the final pot will end up as 15 + 2 * (75+34) = $233

An equity calculator will tell you what equity your hand has so the question is do you have more than $34 of equity in this pot, if you don't you should fold at this point.

You say your equity is 22.73% so if you stay in the hand you pay $34 to 'own' 22.73% of $233 and in the long run this is $52.96
It costs you $34 to call to realise your final pot equity of $52.96. It would be a good call. Note that it doesn't matter what you put in previous to this final bet only the final complete pot size and the amount to call to stay in it.
Here it cost $34 and you get $52.96, so calling at this point nets you $18.96 in the long run.
Typically for allins your needed equity to break even is (the cost to call)/ (Final pot size including your call)

Don't forget that you have to use a sensible range for the villain's hand to make sense.

It's pretty important to be able to determine whether the decisions you make are going to win or lose money for you overall, yes. Like most math, it gets easier with practice.

So I would be considered running $52.96 below EV in this hand? Since I ended up losing the hand? I'm just trying to calculate how bad I'm running in all in pots kind of like how HEM does.

Yes, your EV was $52.96, so since you won $0 you're $52.96 under EV, just like if you'd won you'd be $180.04 over EV.

Sorry I thought you just wanted to know how to calculte the EV of the $34 call decision, not what HEM is doing.

HEM only calculates adifference of EV in specific spots, only when the hand goes all-in before the river for all players involved. You lost a bit of allin EV on this hand but in the long run it doesn't matter, if you see a graph of several thousand allins the actual win line bobbles about a little wider than the allinEv line but as the number of hands increases the difference between the two is relatively less and less important.

In this case HEM would only calculate the EV diff for the turn $34 call point onwards so the final pot would be $233 and you 'own' 22.73% of it so in the long run you expect $52.96 but in general you never get exactly what you are 'owed' in any specific hand as you either win or lose.
In the hand you lost so you got $0.00 and the allInEv should show
$0.00 -$52.96 = -$52.96
ie, you got $52.96 less than expected.

If you had won you would have got $233 and so the allInEv would show
$233 -$52.96 = $180.04
ie, you would have got $180.04 more than expected.

Okay thanks a lot buddy, this is exactly what I was looking for but I was having a tough time explaining it

You wouldn't need to do that at a table because you're already all in. The calculation you'd need to do would be more like this.

The turn is a 9 giving you a set and a full house draw. There is $15 in the pot. Your opponent bets $15. You raise to $50. Your opponent now moves all in with his remaining $120 in chips ($35 call plus $85 more). Should you call?

First, let's say your opponent is very tight and you know he wouldn't do this without a straight. So assume you're behind. You can win if you make a full house and you have 10 outs for that, which is about 4:1 against. Add up what's in the pot. In a real game, you can look at the chips and figure it out. If you're following this example, it adds up to $200 and it's $85 to call.
$200:$85 is only about 2.5:1 and you're not getting the pot odds you need to call, so you fold.