Hi there.  I wanted to talk about balancing dungeons and encounters.  It seems to be something a lot of DMs, especially newer ones, have questions about so let's get into it.  I'll share how I do it, and please let me know how you do it because I'm interested.  

First of all let's differentiate the terms "dungeon" and "encounter".  An encounter is a single high stakes combat where the players are full life and resources, and will more than likely long rest afterwards.  A dungeon is a generally hostile environment that the players are actively exploring that contains a series of mini encounters.  

Most people are likely familiar with the easy-medium-hard-deadly scale with encounter balancing, which you can find in Encounter Builder.  Those aren't useful in my opinion but the Daily Budget value, (notice that), is very useful.  If the Adjusted Exp for the encounter equals the Daily Budget, then that should make for a good, challenging single encounter for a tactically competent group of players.  They will likely win, but not necessarily if they get unlucky or play it poorly.  

As for dungeons, double the Daily Budget and disperse that amount about the area in clumps of adjusted exp per each mini encounter.  You can count traps as easy-deadly encounters depending on how dangerous they are.  Again assuming a tactically competent group of players, this will be a challenging dungeon that needs to be respected.  They should need to short rest at some point, and if things go poorly will need to retreat before clearing the place.  

Well I guess that's all.  Feel free to let us know how you balance things.  

I never do single encounters with a long rest immediately afterwards. That tends to favor per-day spellcasters and make short-rest focused classes, like Fighters and Warlocks, feel useless. Plus, in my experience, if you go above a Deadly encounter (1/3 of the daily XP budget) the players will likely lose due to the monsters' sheer offensive power.

As for the dungeons, I usually use just the daily budget, but make all encounters Deadly, though I'll usually throw a trap or something on top. (Easy and Medium encounters are often laughable pushovers so I almost never use them.) That translates to three fights in the dungeon, which is fine, as my dungeons tend to be small and linear. It's nice because players can easily clear the whole place in a single 4-hour play session. I plan for two short rests within the dungeon, usually one after each fight—if the players need to long rest or retreat, that's fine, but they'll likely fail their mission objective, especially since the monsters are wise to what's going on.

Outside of dungeons I generally run 2-3 adventuring days with little to no combat at all because it feels more realistic to me and honestly, combat is the slowest part of the game. So a Medium-Hard fight here or there progresses the plot and maintains verisimilitude, but I don’t honestly expect it to be enough danger in a single day that I really worry about balance. (It’s kinda like the fiber powder I mix into my coffee every morning, keeps things moving regular like without filling me up or slowing me down.)

But after a few days, all of that puzzle solving, social interaction, and clue gathering will inevitably lead them somewhere that someone doesn’t want them to go. That’s when I bust out the meat grinder and they have 3-4 combat encounters back to back to back to back, and the easiest one is guaranteed to be at least Hard, and the rest are all Deadly+. (You know when that little bar in the encounter builder geys filled up goes all the way red? Yeah I keep adding stuff and don’t even do the math anymore since I can do just as well going with my gut. Basically, I don’t even try to make the combats “winnable,” I try to make them so challenging that by the end of that “day,” the players are just as spent and exhausted as their characters.But they keep winning them anyway. They just keep finding ways to succeed no matter what I throw at them.

Admittedly, we play with a higher than normal amount (and power level) of magic items because our main DM likes to make it rain cool shi—stuff on his players. In his opinion that’s part of what makes heroes awesome. Like how Conan found the Legendary Sword of Crom (aka: The Atlantan) when he was still the equivalent of 3rd-level character. For example, when I rotated into the DM’s seat for the current story, the first thing I did was give an excuse for the party’s employers to “appropriate” three Major Legendary items and two major Very Rare Items from the party of 4 11th-level PCs. (I’m talking Robe of the Archmagi level stuff, in fact that was one of the confiscated items.)

They each still have at least 2-3 Uncommon and 1 Rare Magic Items plus consumeables, And I am also dropping some fun toys of my own creation on them as well because one of my favorite parts of the game has always been homebrewing unique stuff nobody will find anywhere else. And I’m almost positive that when we switch chairs again the he will simply return all of that richatuff right back to the party, but balancing stuff will be on him at that point so it’ll basically be OPP at that point. But he might say the Boons (additional feats) the party is currently reviewing could wear off too. Again, that’s up to him when we switch backnagain so I ain’t sweating’ it. (Not my circus, not my monkeys.)

But I also have a secret weapon to ensure that every fight ends up exactly as tough as in needs to be, no more, and no less.

I “hot fix” the encounter when necessary. If the fight turns out To be too easy, a monster’s HP migh double mid combat. (One time I even tripled a monsters HP over the course of the encounter.)
   Another fight turned out waayyy tougher than I had intended and they were only on their 2nd fight out of the 4 I had planned. After three full rounds of combat not a single PC had done a single point of damage to that thing but they were literally getting eaten alive. Considering that the average fight in 5e is over in 3-4 rounds I was worried. So on the fourth round when someone finally rolled as high as a 19 total on an attack roll, that was the exact instant that monsters AC dropped from 20 down to 19. 🤫
   The next fight (#3/4) was much more deadly than the first two had been, but the enemies came in waves so it was manageable, it still lasted over 12 rounds and took us 2 full 3.5 hour sessions to complete it. nd that fourth fight got adjusted downward before they even walked through the door one of them got off a luck sleep and the fight was suddenly much shorter than expected, much to their relief. Because by that one they were scraping the bottom for whatever they had left in the tank.

But the players never see those levers being pulled behind the green curtain DMs’ Screen. They have absolutely no way of knowing how many HP a creature has when the fight started, they only know how much damage it took the win. So if those two numbers turn out not the be the same it doesn’t really matter because I’m the only one who knows and it isn’t metagaming when the DM does it. 😜

Quote from NaivaraArnuanna >>

I never do single encounters with a long rest immediately afterwards. That tends to favor per-day spellcasters and make short-rest focused classes, like Fighters and Warlocks, feel useless. Plus, in my experience, if you go above a Deadly encounter (1/3 of the daily XP budget) the players will likely lose due to the monsters' sheer offensive power.

As for the dungeons, I usually use just the daily budget, but make all encounters Deadly, though I'll usually throw a trap or something on top. (Easy and Medium encounters are often laughable pushovers so I almost never use them.) That translates to three fights in the dungeon, which is fine, as my dungeons tend to be small and linear. It's nice because players can easily clear the whole place in a single 4-hour play session. I plan for two short rests within the dungeon, usually one after each fight—if the players need to long rest or retreat, that's fine, but they'll likely fail their mission objective, especially since the monsters are wise to what's going on.

Yes, you might be right that it tends to favor full casters who can dump all their spells, but sometimes the situation is unavoidable.  If the players pick a fight or a powerful enemy catches up to them, you have a single large encounter on your hands.  Just an inevitability of DMing.  You can’t just say “I never do this.”  

So you use just a single daily budget for you dungeons?  Makes sense for a smaller one that is intended to be fully cleared without much trouble.  Depending on how skilled to players are at dungeon crawling. 

True, I should say I never plan it. Even if an old enemy appears and attacks in town, though, I still count that as another “room” in whatever dungeon they’re doing that day. Many of my “dungeons” are actually journeys, investigations, or even military battles, but the fights per day and the way I balance them remain the same. As for when players pick fights, there’s no need to balance then. They’ll stop the commoner shopkeeper, and get stomped by the knight captain and his guards. At that point, balance is out the window.