If you download thearcheryprogram and input all your data you can look at a shot replicator that shows elevated and depressed shot angles.
Or you can look at it this way. When you shoot a fixed pin site on level ground at the target 20 yds away you are lofting the arrow to get it to the spot. The amount of loft for your 20 yd shot depends mostly on the speed of your arrow. As soon as the arrow clears the bow gravity starts pulling it to the ground and on a level shot this pull is perfectly perpendicular to the flight path of the arrow so the trajectory of the arrow receives the "FULL" effect of gravity. The arrow is going essentially straight and level and gravity is pulling straight down.

Now if you get up in your treestand and point your bow down at a depressed angle for a 20yd shot (when I say 20yd shot I mean the distance from your front foot to the target, same as the level shot) if you use the same 20yd pin and hold spot on your arrow will hit high. This is because gravity is no longer pulling perfectly perpendicular to the flight path of the arrow. The arrow is getting the same amount of loft it got for the level shot but the flight path of the arrow is at a downward angle. Gravity still pulls the same but since the flight path of the arrow isnt perfectly perpendicular (like the level shot) to gravity's pull the arrows trajectory only recieves a "partial" effect of gravity's pull. In short the arrow doesnt drop as much when you shoot it downhill or uphill for that matter. Like I said in the beginning, this assumes your shot ranges are the same distance and you're using a fixed pin site (not a pendulum).
I imagine there are some formulas out there for gnats assing this stuff but during hunting situations I'm judging distance with my eyes and calculating arrow drop based on how depressed the shot is so a calculator wouldnt do me any good in the treestand. I think thearcheryprogram will give you the most exact answer.

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