According to the rules for passive checks (PHB, p 175), having advantage on a check translates to a +5 bonus to the corresponding passive score.
Lots of monsters have Keen Senses, which grant them advantage on Perception checks under certain circumstances. Something I've done ever since the early days of 5e is make a note of this in monster statblocks.
For instance, a wolf has Keen Hearing and Smell, granting them advantage on Perception checks that rely on hearing or smell. By default, a wolf's passive Perception score is 13. Using the above noted rule, their passive Perception score would increase to 18 for the purposes of hearing or smelling. I make it so the Senses line in their statblock reads "passive Perception 13 (18 w/ sounds and scents)". I do this for all monsters / NPCs with a variation on the Keen Senses trait.
I'm just curious to know if anyone else does this, or am I the only one?
I do use the +5, but I do not write it dowm. If the perception could utilize the listed 'keen' sense the passive perception rises by 5.
My full process is follows when someone is hiding and I want to determine if the 'enemy' will detect them:
1.) Check to see if they have the conditions to maintain the hidden status (no direct and clear line of sight unless target is distracted, etc...)
2.) Determine passive perception.
3.) Apply modifies, such as advantage or disadvantage (but also circumstantial modifiers as well - I give bonuses for distance, for example).
4.) Check - does stealth exceed modified passive perception? If no, they are detected. If yes, go on.
5.) Determine if the observer is searching, inactive, active or distracted.
6.) A searching observer is actively trying to be perceptive, such as a guard that is doing their duty. They get a perception roll to see if they can improve upon their passive perception.
7.) An inactive observer is one that is not trying to be observant, such as a guard that is on watch, but they're bored and not great guards. Generally speaking, they're not trying to be observant, but they're not actively doing anything else, either. They get to roll perception to beat their passive perception, but I apply disadvantage to that role. Note that this gives them about a 1 in 4 chance of beating their passive perception.
8.) An active observer is one that is not trying to be observant and is actively doing something else with their action. This could be dashing (moving at 'full speed'), fighting, spellcasting, or something else. They get no perception roll - they are reliant upon their passive perception.
9.) A distracted observer is one that had their attention intentionally drawn away by someone else. They also get no perception roll and are reliant upon their passive perception - effectively being in the same boat as an active observer - but they had disadvantage on that passive perception (-5). Additionally, you do not automatically lose hidden against these observers if there is line of sight.