Is there a rule of thumb for when "help" is better than making an attack?

Question

For simplicity, let's say that my reasonable combat actions are either making a melee attack or aiding another fighter doing the same. Is there a quick rule of thumb for deciding which is better in terms of average damage done?

How do

• differences in the two fighters' attack modifiers,
• differences in damage dealt, and
• the target's relative AC

factor in? Since it's basically just moving extra d20 from me to the other person, it seems like it's better to Help if the other character has either better to-hit or better damage, unless it's really easy for us both to hit and both do damage. How does the actual math work out, and where's the switchover point for that "unless"?

Answer 1

Let's work an example here. And then see if we can work out something of a rule of thumb.

Let's say we have a L5 life cleric and a L5 rogue (of any stripe). The Cleric has burned (or wants to save) his spell slots so he's stuck with cantrips or his melee attack.

They've both used their abil up to get their primary attack stats up to 18. And we'll give their target an AC of 18 and a Dex save of 4. I'll use my DPAD calculator for this.

If they make straight attacks they do

 Rogue:  11.9 
 Cleric: 4.5 

If they cleric uses his action to give the Rogue Advantage, the rogue will do

 Rogue: 15.7

This is a net win for the party and is something the Cleric should do with his action. Using Help for the rogue is a good idea if the rogue does not have another way to get advantage.

There's a reason I chose the cleric here though. They lag a bit behind other potential melee classes in damage as their extra damage options are later than extra attacks/damage options are for the rest. This would also apply to a wizard who is out of spells, though their cantrips tend to do slightly more damage as they are attacks rather than save effects.

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So if you're a caster without a great basic attack (or down to cantrips for whatever reason), and the thing you are facing is a tough nut to crack (think: you need to roll 16+ to hit him), you're probably better off using your action to give advantage to a party mate who can do big single hits.

The important thing here is to remember the single attack focus here. It doesn't do you a lot of good to give advantage to a fighter whose damage for the turn is going to be spread across several attacks. This is a power that is meant for your cleric or wizard to make the Rogue's strike bigger.

The rogue can usually get her sneak attack off by herself (between the fact that advantage is unnecessary at times and she can often use her bonus action to get it), but occasionally she may need help from an ally. The example shows that even if she can use SA advantage can still help more than a cleric's cantrip.

Answer 2

Helping in combat is very situational. It increases the chance of a critical hit from 5% (1 in 20) to 9.75% (39 in 400), decreases your chance of an automatic miss to 0.25% (1 in 400), and moves the 50% marker (the number you can expect to roll equal to or higher than) from 11 up to 15.

Because of this, it pays to take Help in combat for the following situations, provided that your ally does not have advantage from some other means. (Since help only grants advantage, it's never worth your action if your ally already has it.)

1. Your ally in attempting an attack which may end the battle, such as a disarm.
2. You cannot reliably deal damage, such as if you have no weapon you are proficient in, have a substantial strength penalty, or are unarmed.
3. Neither you nor your ally can reliably hit, but they would do more damage if they hit.

Answer 3

Mathematically, the seemingly easy conclusion of "you double his hit chances" is wrong. Actually, you cut in half his miss-chance.

However, looking at it from a purely mathematical point is very, very time consuming because there is so much to factor in. Ok, granted, if you both have a weapon and you both do a standard attack, then yes, you can have math tables. But more often than not, you don't. Because if you were doing standard attacks with standard weapons, god that would be boring. So you have specials. And now it gets interesting. What your friends special attack worth? And what do you trade in for it? Do you have a special attack, too? Do the special attacks can be done all night, or do they exhaust like spell slots?

Helping your friend means his attack will hit more likely. On the other hand, your attack has no chance to hit at all. So if

your hit chance * your average damage

is smaller than

(100 - (100 - (his hit chance)) / 2) * his average damage

then go ahead and help him.

Hit chance means the percentage. If you need a 17 on a d20 to hit, that's 20% hit chance for example (a d20 has 20 sides, so each side will come up 5%, and for a 17 you can use 4 sides, 17, 18, 19, 20). This formula does not take criticals in account.

But I would say for the sake of having fun, skip the math lesson. If your friend does something cool, that should land straight in your opponents face, go give him a hand. This is a game, have fun playing it. Math can wait for monday morning.