Well, the clue's in the title. 

You've done your normal attack/s and now it's your hasted action. 

Can you hold your hasted action?

Thanks.

I believe the answer is "no".

The hasted action has an explicit list of what actions can be taken and the "ready" action is not among them.

Quote from Septimus_Pilgrim >>

Well, the clue's in the title. 

You've done your normal attack/s and now it's your hasted action. 

Can you hold your hasted action?

Thanks.

Straight up "no".

Haste

Choose a willing creature that you can see within range. Until the spell ends, the target's speed is doubled, it gains a +2 bonus to AC, it has advantage on Dexterity saving throws, and it gains an additional action on each of its turns. That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.

When the spell ends, the target can't move or take actions until after its next turn, as a wave of lethargy sweeps over it.

The Ready action is not one of the options you can take with the action granted by Haste.

If you can use Hasten to attack then use the Hasted action to attack and the regular action to do Ready. I don't see anything in the text that prohibits that, since it does not specify that the additional action is subsequent to the regular action.

That wasn't the question, but yes I see where you're going: the order of "hasted action" & "actual action" on your turn doesn't matter.

You can do whatever you want with your actual action, but you can only do what Haste says you can do with its "action", which cannot be used to take the Ready action.

Thanks everyone.

Quote from BioWizard >>

If you can use Hasten to attack then use the Hasted action to attack and the regular action to do Ready. I don't see anything in the text that prohibits that, since it does not specify that the additional action is subsequent to the regular action.

I was asking because if I held my primary action and I have multiattack I'm effectively losing 1 or 2 attacks whereas, as you can only attack once with your hasted action once holding it wouldn't lose you anything. That was my thinking anyway.

Well, thanks to all for clearing that up!

Quote from Septimus_Pilgrim >>

Thanks everyone.

Quote from BioWizard >>

If you can use Hasten to attack then use the Hasted action to attack and the regular action to do Ready. I don't see anything in the text that prohibits that, since it does not specify that the additional action is subsequent to the regular action.

 

I was asking because if I held my primary action and I have multiattack I'm effectively losing 1 or 2 attacks whereas, as you can only attack once with your hasted action once holding it wouldn't lose you anything. That was my thinking anyway.

Well, thanks to all for clearing that up!

 If by "Multiattack" you mean the "Extra Attack" class feature, that only applies when you take the Attack action on your turn. If you Ready an attack to trigger with your reaction on someone else's turn, you can only make one attack.

Quote from jd2319 >>

Quote from Septimus_Pilgrim >>

Thanks everyone.

Quote from BioWizard >>

If you can use Hasten to attack then use the Hasted action to attack and the regular action to do Ready. I don't see anything in the text that prohibits that, since it does not specify that the additional action is subsequent to the regular action.

 

I was asking because if I held my primary action and I have multiattack I'm effectively losing 1 or 2 attacks whereas, as you can only attack once with your hasted action once holding it wouldn't lose you anything. That was my thinking anyway.

Well, thanks to all for clearing that up!

 If by "Multiattack" you mean the "Extra Attack" class feature, that only applies when you take the Attack action on your turn. If you Ready an attack to trigger with your reaction on someone else's turn, you can only make one attack.

 Yeah, that's what I'm saying. I wouldn't want to hold my regular attack action as it encompasses my extra attacks and would therefore waste them. That's why I wanted to know if I could hold my hasted action, so as not to waste the extra attacks.

Quote from Septimus_Pilgrim >>

Quote from jd2319 >>

Quote from Septimus_Pilgrim >>

Thanks everyone.

Quote from BioWizard >>

If you can use Hasten to attack then use the Hasted action to attack and the regular action to do Ready. I don't see anything in the text that prohibits that, since it does not specify that the additional action is subsequent to the regular action.

 

I was asking because if I held my primary action and I have multiattack I'm effectively losing 1 or 2 attacks whereas, as you can only attack once with your hasted action once holding it wouldn't lose you anything. That was my thinking anyway.

Well, thanks to all for clearing that up!

 If by "Multiattack" you mean the "Extra Attack" class feature, that only applies when you take the Attack action on your turn. If you Ready an attack to trigger with your reaction on someone else's turn, you can only make one attack.

 Yeah, that's what I'm saying. I wouldn't want to hold my regular attack action as it encompasses my extra attacks and would therefore waste them. That's why I wanted to know if I could hold my hasted action, so as not to waste the extra attacks.

That's one of many reasons why you can't take the Ready action with Haste, and also why Extra Attack only applies on your turn.

So I am rembering the same limitation that we're all talking about here, that the action you Ready is just a single attack and not a full Attack Action (benefiting from your Extra Attack feature).... but I'm not actually seeing that in the text? Am I blind?

Ready

Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on your turn, which lets you act using your reaction before the start of your next turn.

First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it. Examples include "If the cultist steps on the trapdoor, I'll pull the lever that opens it," and "If the goblin steps next to me, I move away."

When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger. Remember that you can take only one reaction per round.

When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell's magic requires concentration. If your concentration is broken, the spell dissipates without taking effect. For example, if you are concentrating on the web spell and ready magic missile, your web spell ends, and if you take damage before you release magic missile with your reaction, your concentration might be broken.

"You choose the action you will take in response to that trigger." How is "I take the Attack action" (and all that that entails) not an eligible choice to make?

It's a stipulation of Extra Attack itself:

Extra Attack

Beginning at 11th level, you can attack three times, instead of twice, whenever you take the Attack action on your turn.

The number of attacks increases to four when you reach 20th level in this class.

You get the "full benefit", that benefit is just restricted to your turn.

CC, you can definitely ready the Attack action. But Extra Attack specifies “When you take the Attack action on your turn...”

Phew, I was worried it was just a mass delusion!

However, that does make me realize that monsters with Multiattack, such as a Black Bear (or Druid Wildshaped as such) get a little more out of Readied actions than I've been playing them as, assuming there was something about the Ready action itself that limited it to a single attack. 

Also, it calls into question the outer boundaries of Bonus Actions which might trigger upon having taken an "Attack action." On the one hand, "Bonus Action" itself does include some "on your turn" language, which probably means that Bonus Actions only exist on your own turn and not others. On the other hand, both Bonus Actions and Reactions fall under the header of a section labeled "Your Turn", and I think we all recognize that Reactions can occur outside of your own Turn. The special Bonus Action Two Weapon Fighting attack does not include any "on your turn" language itself, so the only thing stopping you from using it after a Readied attack would be a limitation on Bonus Actions in general being taken off-turn. I'd give that limitation a.... probably pretty solid 100% RAI rating, but only about a 90% RAW rating given that "your turn" may not really mean "your turn" each and every time it's found because of that heading.

Anyway, the Multiattack stuff at least is interesting for a Druid or someone who is Polymorphed.

Quote from Chicken_Champ >>

Phew, I was worried it was just a mass delusion!

However, that does make me realize that monsters with Multiattack, such as a Black Bear (or Druid Wildshaped as such) get a little more out of Readied actions than I've been playing them as, assuming there was something about the Ready action itself that limited it to a single attack. 

Also, it calls into question the outer boundaries of Bonus Actions which might trigger upon having taken an "Attack action." On the one hand, "Bonus Action" itself does include some "on your turn" language, which probably means that Bonus Actions only exist on your own turn and not others. On the other hand, both Bonus Actions and Reactions fall under the header of a section labeled "Your Turn", and I think we all recognize that Reactions can occur outside of your own Turn. The special Bonus Action Two Weapon Fighting attack does not include any "on your turn" language itself, so the only thing stopping you from using it after a Readied attack would be a limitation on Bonus Actions in general being taken off-turn. I'd give that limitation a.... probably pretty solid 100% RAI rating, but only about a 90% RAW rating given that "your turn" may not really mean "your turn" each and every time it's found because of that heading.

Anyway, the Multiattack stuff at least is interesting for a Druid or someone who is Polymorphed.

No to readying Multiattack, for the same reason you can't ready Extra Attack--it only works on the creature's turn.

Multiattack

A creature that can make multiple attacks on its turn has the Multiattack action. A creature can't use Multiattack when making an opportunity attack, which must be a single melee attack.