It'd probably be better for one of the two Modifier: Bonus to be Modifier: Set, so that it doesn't just add to a different Unarmored Defense like Monk's or Barbarian's, potentially giving 10 + Int + Cha + (Wis or Con).

I'm making a custom dragonborn race from scratch with it's own options of what family they belong to, and one of the options is supposed to have an unarmored AC of 11 + DEX at 1st level, and then 12 + DEX at 6th and so on. The problem is I can't find a modifier type that lets me make it so that it increases at specific levels? I am grateful for any help I can get! :)

 I wonder how well it'd work if in the trait, you made an Option for each upgrade. So like "Upgrade1", Required Character Level: 6, check the Is Granted checkbox, add modifier for Set Unarmored Armor Class  - 12 + DEX

The system should use the best Unarmored AC calculation. But I haven't tried doing this myself.

Is there a way to add proficiency to AC (Including the increased prof as one levels up)?

Yes! There's a text box below Fixed Value, called Additional Bonus Types. Click in the box and you'll be able to select Proficiency Bonus, which will be added to the modifier.

Why use "bonus" here instead of "set" what's the difference? I'm trying to do 10+Dex+Wis but the double Set>Unarmored>Dex/Wis with Ignoring the Dex bonus isn't working for me. The wisdom modifier isn't being added at all

The Wis wasn’t being added because of the Set Modifier. If you tell the system to use Modifier->Set for two different things, only one thing can be “Set” at a time, so the system will only use the higher value. That’s why it’s better to use Modifier->Bonus in that situation.

Hey guys. Looking for some help with a new class I'm trying to build into DNDBeyond from a purchased 3rd party book. Here is the the portion I am currently trying to input:  

" While you are not wearing any armor, your Armor Class equals 11 + your Dexterity modifier + your Constitution modifier. "

Now I seem to have the DEX and CON modifiers inputted correctly and they are working on my test character when he is not wearing armor. When armor is applied (Light Armor) it goes back to the armor (11) plus the DEX Bonus (not from the feat.).

Right now the modifiers i have on are Bonus-> Unarmored Class -> CON, Bonus -> Unarmored Class -> DEX, both working as said.

You don’t need to add the Dex, that’s automatically applied. For a calculation of 11+Con mod + Dex mod all you need is the following modifier.

Modifier: Set->Subtype: Unarmored AC->Ability: Con->Fixed Value: 1

Thanks IamSposta. Really appreciate your input and knowledge. Worked perfectly. 

So... it seems dnd beyond hate me or something. I'm trying to make two races, each with their own unarmored ac. One like the tortle with a flat AC of 17

so set - unarmored ac- fixed value:7

Ignore- unarmored dex bonus

The other one is supposed to be 13+dex
so set - unarmored ac- fixed value 3.
but for some reason the first one works with the fixed value, but is refusing to ignore the dex. so dex 16, ac 20.
And the other one just isn't working at all. dex 16, ac 13. I've been doing everything I can for hours now, and it just doesn't work.

After you added the Modifiers, did you remember to re-save the entire race using the main [SAVE CHANGES] button under Basic Information? If you don’t the system won’t pick up your changes. After that it can sometimes take up to 20 minutes for those changes to filter to the character sheet. And your character might be stuck on an old version of the race, so you may need to “wake it up.” Please see the General Homebrew FAQ #s 6 & 6-B for more information: (https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/131411-a-homebrewers-how-to-faq).

Holy crap you were right! Shouldn't be surprised though, you're good at this. Thanks mate.

I’m trying to do a basic unarmored AC of dexterity (13+dex for those that are curious) and no matter which method I try, or in which way I reload the character I’m using to see the changes, nothing’s working. It still shows the base AC as 10.

Never mind. I fixed it. Just needed to switch the Set to Bonus and re-apply the race in the character editor

I am trying to do the same, but I keep getting a crazy high AC of 26 following these steps. When I feel like it should only be 16 for my math. Either my math ain't matching and I am misunderstanding how this bonus stacks, or I am entering something wrong. My Homebrew Race has an Unarmoared AC of 13 + Constitution Modifier. In the homebrew creator I currently have:

Modifier -> Set -> Unarmored Armor Class -> Fixed Value -> 3
Modifier -> Bonus -> Unarmored Armor Class -> Ability Score -> Con
Modifier -> Ignore -> Unarmored Dex AC Bonus

When I go into the character sheet and look at the AC I have the base of 10, it is then adding 13 Unarmored AC onto that, and then the Constitution Modifier on top of that which is a +3 in the case of this character. Is that right? Seems incredibly high for an unarmored first-level character.

** Edit - I tried changing Set to Bonus for the fixed +3 to Unarmored AC, and this did stop it from adding an additional +13 to the AC and only the +3. However, now it doesn't seem to removing the Unarmored Dex Bonus properly as I still see it showing up. In addition to this, It is also not removing the +3 and the Con Modifier Bonus when I equip armor. Now I really don't know what is going on. **

Try this:

• Modifier: Set->Subtype: Unarmored AC->Ability Score: Con->Fixed Value: 3
• Modifier: Ignore->Subtype: Unarmored Dex AC Modifier

Then re-save the whole homebrew, wait 20 minutes, and then remove the homebrew from your PC and add it back again and see if that fixes it.

Okay, new quandary for this thread. I'm setting an unarmored defense, but what if I want the feature to also add a +1 to their AC while they wear armor? Is that possible while homebrewing it? Or do I have to have my players do that manually here on D&D Beyond?

You would also apply the following Modifier:

• Modifier: Bonus->Subtype: Armored Armor Class->Fixed Value: 1

Huuuuuge! Thanks Sposta!!