Does the sorcerer's Extended Spell metamagic option extend the duration of a spell exponentially or linearly? [duplicate]

Question

When it mentions that you can spend 1 sorcery point to double its duration, up to a maximum of 24 hours, does it mean that every time you spend a sorcery point you add the original duration again? Or does it exponentially double the duration?

For example, if I spend 4 sorcery points on a 1 minute spell, does it become 5 minutes (1 minute duration added four times) or 16 minutes long (1 minute doubled four times)?

What I meant by this question is just using Extended Spell on a spell once, but using more than 1 sorcery point on it as per the metamagic's description.

I know you can't re-extend a spell if it's already active, but I'm talking about the initial casting, where you can spend multiple sorcery points to double the spell's duration.

Answer 1

Extended Spell only extends the duration once by doubling it.

A caster can't use Extended Spell multiple times on the same casting, and the feature doesn't accommodate using multiple sorcery points at once.

This is addressed directly in the Sage Advice Compendium

At the bottom of page 5 of version 2.4 of the SAC, it says:

Metamagic rules state you can’t use multiple Metamagic options on a single spell. Can you use one option multiple times?

A sorcerer can use one Metamagic option once in the casting of a spell, not the same option more than once. For instance, a sorcerer can’t quadruple the duration of a spell by spending 2 sorcery points on Extended Spell.

This is further discussed in this Q&A: Can you use Extended Spell Metamagic more than once?

Can't pump more sorcery points through Extend Spell

The wording is that you can spend one point.

When you cast a spell that has a duration of 1 minute or longer, you can spend 1 sorcery point to double its duration...

A wording that would have permitted multiple points would be "...for every point spent.." or "... can spend 2 sorcery points to quadruple it's duration and so on..."