How many luck points does it cost to get a better attack roll with Lucky?

Question

For the Lucky feat there is something I need clarified. The feat says (PHB p. 167):

"... Whenever you make an attack roll, an ability check, or a saving throw, you can spend one luck point to roll an additional d20. You can choose to spend one of your luck points after you roll the die, but before the outcome is determined. You choose which of the d20 is used for the attack roll, ability check, or saving throw..."

My DM interprets this as:

1. Spend 1 luck point to roll a d20
2. Spend 1 more luck point to replace a d20 roll with the new "lucky roll" if you want... otherwise you have used up only 1 point to roll the d20

I always read it as:

1. Spend 1 point, roll a d20 for luck. Replace the old roll with no additional cost

What is correct?

Answer 1

Your DM is wrong.

The ability wouldn't have 3 points if you had to spend 2 to use it once. The confusion in the wording is the second sentence. All it does is clarify when the luck point can be spent.

Example:

You are climbing a mountain and there's a rockslide, the DM says, "Make a DEX save to see if you get knocked off."

You roll a fail on your save. Instead of taking the fail, you can spend a luck point to see if the gods of luck are with you and help you make your save. You roll another D20 as your save, and you choose which of the two you take for your roll.

Answer 2

Your DM is definitely misinterpreting the rules.

"... Whenever you make an attack roll, an ability check, or a saving throw, you can spend one luck point to roll an additional d20. You can choose to spend one of your luck points after you roll the die, but before the outcome is determined. You choose which of the d20 is used for the attack roll, ability check, or saving throw..."

The first part of the feat, highlighted in bold, tells what happens when you have the feat and you use a luck point. The latter part, highlighted in italics, states when you are able to use a luck point. Which is before your failure has been roleplayed by you and your GM before the results of the roll have been disclosed.

So what this means is that you can immediately use a luck point after rolling a 1 on the d20, roll a second d20, and take the result of the second roll.