After starting on Dungeon of the Mad Mage (actually after finishing Dragon Heist in 26 - Downtime 2) we are no longer using Milestone Levelup.
Instead we will be using a simplyfied XP method: Number of Medium Encounters Completed by the Party.
Sometimes completing a dungeonlevel and defeating all enemies will get you to the next level up. Sometimes two dungeonlevels will be required.
But since some parts of the dungeon-levels can be bypassed, you might sometimes need more than two dungeonlevel.
Solving social encounters will also get you XP - normally 1/2 or 1 XP, but as much as 3 XP. You do not need to murder hobo your way through every encounter in order to level up.
Encounter difficulty is based on the rules in the DMG.
This handy calculator makes it easer: https://kastark.co.uk/rpgs/encounter-calculator-5th/
Need 18 XP to level up.
Current XP: 18 XP
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Need 18 XP to level up.
Current XP: 18 XP
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Need 18 XP to level up.
Current XP: 18 XP
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Need 18 XP to level up.
Current XP: 20 3/4 XP (Excess lost because you are ahead of the dungeon. And got XP for the Aboleth twice.)
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Need 11 XP to level up.
Current XP: 4 1/4 XP
Inspired by - “Putting the Chips Down” section: https://chaoticneutraldm.com/2020/02/14/dms-guide-to-undermountain-1-thru-3/
This says that Hard Encounter is not needed. As Deadly Encounter is worth double of Medium Encounter. Let's see is that is the case - if it is, then remove Hard, and dial Deadly down to 2 XP.