I don't really keep track of milestone or XP which is a bad idea. Can someone explain to me how it works, it's weird that I don't already know. Because I've run multiple campaigns without this knowledge, I think that I was levelling my players up way too quickly. They would level up after every other major battle, so a quick goblin ambush or killing a few animals wouldn't count. So after two major battles, level up. This led to one of my campaigns finishing at level 8 (it was a very short campaign). How should I go about doing this, and how do most people deal with it?

XP: Each encounter is worth an amount of XP based on the Challenge Rating of the enemies, and how many there are.  There are online calculators you can use that show how much XP such encounters are worth per player-character.

Milestone:  When the party accomplishes a significant task, like the completion of a major story arc, they level up.

What you're doing allows the party to level up much faster than most tables, which gives the players more oportunity to play with higher-level class abilities, but does shorten the campaign, because they effectively become demigods much sooner.  If you want the game to go longer or the leveling to go slower, maybe have two big battles to get to L2, then they need to win 3 major battles to get to L3, etc.  That way the more they grow, the more it takes to get more powerful.  Keep in mind, if you want the party to make it to L20, doing this will make the game take multiple years to complete.

I was in a DCC game where he didn't look at xp or narrative climaxes at all.  The character surviving one session got it from L0 to L1, then 2 more sessions to get to L2, etc.  Granted, DCC only goes to L10, and even doing leveling that way, very few characters ever survive to L5.

There's no right or wrong way to go about leveling, and some groups really enjoy leveling fast. It just depends on what you want the power-up experience to feel like. 

XP is great because your players know exactly how far away they are from leveling up, and every battle allows them to get a little closer. XP's potential drawbacks are that 1) it can encourage combat as the solution to every problem, since there is no pre-existing XP value for puzzles, social encounters, skill challenges, or exploration, and 2) the DM has to calculate and distribute XP, which can be confusing or tedious for newer DMs. 

Milestone is great because the DM can set the pace for the adventure and when significant moments (combat or otherwise) are reached, and level-ups become a welcome surprise. Milestone's potential drawbacks are that 1) the players are in the dark about when they will reach their next power-up, and 2) the DM has to figure out what those milestones will be. 

What you've been doing is just a fast-paced milestone campaign. Whether it's big fights or X number of sessions, that's been the criterion for your players' power-ups. And if that's what you want and what they enjoy, that's perfectly fine to keep doing. If they're advancing faster than you like, though, you can plan a little ahead and pick the moments or really important battles that you will let them level up after. Maybe instead of awarding them a new level after a hard fight, you wait until the BBEG of that current arc is defeated, or they do something that has a dramatic impact on the story world. 

Personally, I run my campaigns as milestone and my players advance very slowly - they went from level 4 to level 11 in 2.5 years of weekly play. I like to let them get very good at using their resources and abilities at each level, and I only bump them up after they survive something tremendous or do something tremendous that is directly linked to the narrative. Combat is rarer in my games than most, too, so RP choices and intelligence-gathering factor significantly into my milestones. That would not be fun at a lot of other tables, but it worked for us.

Something seems odd here. If you're not tracking XP or milestones, how are your players leveling up? Once every couple fights is pretty fast for XP, but a milestone system would mean they only go as fast as you choose to let them.

Are you miscalculating how much XP the encounters are worth? I think in my first game, I got it into my head that the XP from each monster was per player, not divided amongst the players, which obviously would've had them leveling up four or five times as fast as they should've if that game had gone on much longer.

Do it by games played, if you can. The below assumes 4-6 hour game sessions, with at least one decent combat per session. Attach a milestone if you like, but it works out this way with XP anyway for me.

• Level 1: Level up after 1 session, or possibly mid-session.
• Level 2: 1 session
• Level 3: 2 or 3 sessions
• Level 4 to 7: 4 sessions
• Level 8 +: 5 sessions

Your PCs will hit level 20 after about 80 sessions, which is probably about right for a full campaign, as playing once per fortnight you should get there in 3 years.

My group now, thankfully, uses milestone leveling... and that's going to look different from DM to DM.

We started the one campaign back in june 2021 (or something like that) and we play every other week (I mean that's the goal it's not always a guarantee and it hasn't always been DnD every time we meet up either) and the campaign is finally starting to finish up now.... Ideally I'd like this current game to be done in like sixish sessions but what will be will be.

I started my players at level 4 and they are currently level 9... and depending on numerous factors they might get to ten before it ends... I honestly don't feel like they need it to compete with what exists (and I'd have to make things harder than they currently are in my head if I do) and while I don't know how things are going to play out I do feel like they have enough items and power level to survive, with right decisions, without needing me to fudge my rolls.

Not like fudging rolls is something I need to do to save them as a DM, I often roll badly as a DM lol

This is fine if you are fine with it.

If you are not, then extend it out a bit more -- maybe four big fights.

As noted above, you are doing the milestone system for them.  I do my milestones by story points (typically one full adventure that could take 15 or 20 sessions easy), ut I know someone who does it this way:

1st session, bump to level two.

after that, it is the level times two in sessions.  This slows it down later on, but lets them get good fun early on.

Pint is this:  you get to do it however you want.

Experience points are great when all you do is dungeon crawls, ime, because then you can just keep pounding away at bad guys. But the rest of the time, it can be a pain as mentioned above. You have to track how much everyone earned, check against their accounting, argue a little, provide bonus xp, and you also have to make sure that you use the right amount for the monsters you throw against them.

I think experience is entirely a personal thing.  XP guidelines in books are just that, guidelines.  So here is my 2 cents.

I agree with Professor Dungeon Master on YouTube that the higher the level, the harder it is to design a game.  The players have so many powers and abilities they can overcome most obstacles, often in a way that is unpleasant from the DM's point of view because they "cheated."  Also, players become much harder to kill after the first few levels, making fights take longer.  It is a "cold war" between the monsters getting tougher and the PCs getting tougher.  While a level 1 character made of glass is not fun to play, a level 12 behemoth who casts a million spells suffers from a worse problem.

For me, I like to get people to level 2 quickly, and then slowly cruise through 2-10, with levels 2-5 being the most fun.  I give XP for killing monsters (roughly what is in a book), completing a major questline (some reasonable (to me) number that I make up), and anything cool the player does: thinking of a good battle tactic, interesting role playing, etc.  For the latter, I keep tally marks on the HP log so I can remember how many bonuses to give, which is 10-20% of the total XP for any given session.  I also agree with Professor DM that low level players should die often; there is a reason all the bakers and farmers don't all run off and become adventurers-because it is dangerous!  This keeps the player levels lower.  If they die, I let them assume an NPC that was 1-2 levels lower than they are.  

You may disagree and your players may want to make god-like characters, but this is what we do and it works for us.  

Leveling is something that is up to the individual DM and group of players. There is no right or wrong answer as to how fast to level.

There is also no right or wrong answer to what levels are more fun to play, what levels make for a good game, or what even constitutes a good game. It varies by group and DM.

Some DMs think characters should have a relatively high chance of dying. Other DMs don't care one way or another or prefer that characters don't die unless due to some specific character decision. Some DMs have troubles with creating high level content because they find the player abilities frustrating. Other DMs love creating high level content just to see the cool ways the players come up with to deal with the situations.

I find some of the differing attitudes between DMs may come down to how adversarial the DM perceives the game to be. Personally, when I DM, I am neutral. I represent the world and the events going on in that world. Those events interact with the players and their decisions. If the characters do something cool, I'll cheer along with the players.

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All of this contributes to what is an appropriate pace for leveling in your campaign. If someone plays Adventurers League, characters can level up after every session though they won't necessarily do so. Other folks feel that higher levels should take longer so they have a non-linear system that increases the number of sessions or big events that the party must face to level as the characters get to higher levels. Other DMs might use a more linear system like two or four major encounters/level. As long as the DM and players are having fun and the DM isn't feeling overwhelmed coming up with content for whatever level the characters might be, then it is all good.

XP leveling is the traditional method for D&D. Each creature has an XP value awarded when they are defeated. Each encounter could also have an XP value assigned by the DM which could be awarded when the encounter is resolved (this applies to both combat and non-combat encounters). Any sort of in game interaction could have an associated XP reward. Total the XP value, divide by the number of characters present and each gets that much XP for the session. This used to be far more significant when every class needed different amounts of XP to level and multiclassing had the XP divided between the classes.

With every class having the same XP progression these days, milestone leveling starts to make more sense. The DM can choose to level the characters up when they have either accumulated about enough XP for the next level or have achieved some specific goals in the game. In the OPs case, they award a milestone level roughly every two major encounters. Perfectly valid. :)

I'm personally taking a "guided milestone" approach. I am tracking the XP the party is accumulating, and then when they get to about where they would level up if doing xp, I find a convenient point for them to level up as a milestone.

I am also remaining conscious of the players and how they are feeling about their characters. If they are still enthusiastically enjoying their newest abilities, then I will postpone a level up. If they seem to be wanting progression, then I will consider leveling them up earlier. The pacing of the game is up to the DM to manage, after all, and if the players are growing bored of their characters, then it's perhaps time to give them a big fight and level them up. If they seem content with the roleplay and aren't so eager for character levels (EG they are building their characters personality, not their ability list), then delay the level up until it seems meaningful.

There are plenty of encounter calculators out there which tell you the xp for defeating them. I've never seen it worth niggling if they don't kill the enemy - in my opinion, an encounter is an obstacle, and if they get past the belligerent ogre by persuasion, it's worth the same xp as if they had killed it - provided you make it about as difficult!