I've been playing Open Legend RPG and I love that the Advantage in that game can be stacked. I love it when players try to strategize and stack as much advantage as possible.

I want to do this in D&D, but triple advantage doesn't really differ much from normal advantage. So, I was thinking of giving a +1 modifier for advantage instead of a double roll. This way players can stack +1 for every clever thing they do.

Will this work or will this throw D&D off balance? Any idea?

PS. Disadvantage could stack as well with -1s.

This is going to be difficult to balance

Having advantage on a roll is roughly equal to having +5 to your roll, and having disadvantage is roughly equal to having -5 on your roll.

Your suggested change would require somebody to have 5 different sources of advantage to get the same bonus as they do now, which seems extremely difficult to get unless you start also house-ruling a lot of ways to get advantage.

And once you start houseruling a lot of ways to get advantage, to try and make up for advantage now being weaker, you're making special abilities that only work when you have advantage a lot stronger.

By changing just this one thing, you're very likely going to have to make a lot of extra changes that will break other parts of the balance.

Giving a +1 modifier is, under the vast majority of circumstances, weaker than giving Advantage

Below is a table with two sets of Columns:

• The possible results for a regular D20 roll, no other modifiers


• The possible results for a D20 roll made with advantage, no other modifiers

beginarrayr
& & textNormal & & & textAdvantage & \
textOutcome & textOdds & text# of Trials & textOdds to Pass & textOdds & text# of Trials & textOdds to Pass
\ hline
text[1] & text5.000% & 1 & text100.000% & text0.250% & 1 & text100.000%\
text[2] & text5.000% & 1 & text95.000% & text0.750% & 3 & text99.750%\
text[3] & text5.000% & 1 & text90.000% & text1.250% & 5 & text99.000%\
text[4] & text5.000% & 1 & text85.000% & text1.750% & 7 & text97.750%\
text[5] & text5.000% & 1 & text80.000% & text2.250% & 9 & text96.000%\
text[6] & text5.000% & 1 & text75.000% & text2.750% & 11 & text93.750%\
text[7] & text5.000% & 1 & text70.000% & text3.250% & 13 & text91.000%\
text[8] & text5.000% & 1 & text65.000% & text3.750% & 15 & text87.750%\
text[9] & text5.000% & 1 & text60.000% & text4.250% & 17 & text84.000%\
text[10] & text5.000% & 1 & text55.000% & text4.750% & 19 & text79.750%\
text[11] & text5.000% & 1 & text50.000% & text5.250% & 21 & text75.000%\
text[12] & text5.000% & 1 & text45.000% & text5.750% & 23 & text69.750%\
text[13] & text5.000% & 1 & text40.000% & text6.250% & 25 & text64.000%\
text[14] & text5.000% & 1 & text35.000% & text6.750% & 27 & text57.750%\
text[15] & text5.000% & 1 & text30.000% & text7.250% & 29 & text51.000%\
text[16] & text5.000% & 1 & text25.000% & text7.750% & 31 & text43.750%\
text[17] & text5.000% & 1 & text20.000% & text8.250% & 33 & text36.000%\
text[18] & text5.000% & 1 & text15.000% & text8.750% & 35 & text27.750%\
text[19] & text5.000% & 1 & text10.000% & text9.250% & 37 & text19.000%\
text[20] & text5.000% & 1 & text5.000% & text9.750% & 39 & text9.750%\ hline
textAverage & 10.500 & & textAverage & 13.825
endarray

From these two tables, we can make a few casual observations:

• For a "coin-flip" roll, where a 10- fails and an 11+ succeeds, giving Advantage to someone is like giving them a +5 on their roll.
  
  
  • Sidebar: the Player's Handbook (Passive Checks, page 175) specifically says to just give +5 to Passive checks that would otherwise have Advantage (or -5 for checks with Disadvantage)
  
  


• There are a few times where your variant might be better, but they're limited.
  
  
  • The only time that giving someone +1 on their roll, which is what your system does, would be strictly better than having Advantage is if they would otherwise need to roll a natural 20 to succeed: in those circumstances, their odds improve from 5%→10%, whereas with normal Advantage, they'd go 5%→9.75%.
  
  
  • For two sources of Advantage, they'd need to be facing a check that requires at least a natural 19 (10%→20% with your system, 10%→19% with normal Advantage)
  
  
  • For three sources of Advantage, they'd need to be facing a check that requires at least a natural 18 (15%→30% with your system, 15%→27.75% with normal Advantage)
  
  
  • On the other side of the spectrum, a +1 bonus is only better than normal Advantage if the roller must roll a natural 1 to fail(5%→0% for your rule, 5%→0.25% for Advantage), a +2 is only better on a roll requiring a natural 2 to fail (10%→0%, 10%→1%), a +3 is only better on a roll requiring a natural 3 to fail (15%→0%, 15%→2.25%)
  
  

Under normal gameplay circumstances, having more than 3 sources of Advantage is, strictly speaking, incredibly unlikely. So as a consequence, replacing Advantage with a strict +1 (stacking) bonus is going to reduce the power of Advantage by a considerable amount.

You'll need to come up with rules for how to handle features like Elven Accuracy

Elven Accuracy, a feat that can be taken by Elves and Half-Elves, has a specific effect that plays off the nature of how Advantage affects rolls:

• [...]


• Whenever you have advantage on an attack roll using Dexterity, Intelligence, Wisdom, or Charisma, you can reroll one of the dice once.

—Elven Accuracy, Xanathar's Guide to Everything, pg. 74

So if you allow characters in your campaign to take this feat, or any feat that has similar effects on an Advantage roll, you'll need to make a decision about how this feat should behave under these circumstances, bearing in mind that being given the option to reroll a single die is far less powerful than being able to do so when it is paired with another die in an Advantage roll.

Adding and subtracting values in the way that you have proposed is very much how 4th edition D&D worked. 5th edition has deliberately stepped away from that with the concept of "bounded accuracy".

The advantage/disadvantage system in 5e is designed to be simple and elegant. As someone who has played and DM'd both editions I really appreciate the simplicity of rolling two dice instead of doing a bunch of last-moment adding and subtracting. If your table really enjoys tactical combat and trying to finesse every angle then I suggest you try 4th edition out as it might appeal to you.

I don't think what you're proposing will work very well in 5th edition, as you can see in the graph in David's answer.

This makes one advantage significantly weaker and it becomes very difficult to reach enough advantages to compensate.

For demonstration purposes, let's take a standard d20 advantage roll minus a flat d20:

On average, this results in about +4 or higher as a benefit. This will require four stacked advantages before you get the approximate benefit of one advantage. You can read further on the effects of advantage in this Q&A.