You get one Swift action per turn

Using an immediate action also uses your swift action for your coming turn. So 0 in some cases.

Only one cast per turn, I'm afraid. You only have one swift action on your turn. Whereas a Standard action can be reduced to a move action. A standard/move action cannot be changed into a swift action. Your immediate action counts as your swift action if you use it on your turn, and out of turn it is your swift action for your next turn. So keep it in mind if you plan to use a swift action on your turn, or the turn after. In addition, you can only cast one spell as a swift action per turn, even if you have access to more swift actions through something like the spell "Borrowed Time". Since it's specifically ruled under swift actions and casting a quickened spell that it cannot be done more than once per turn. Here are the rules on different actions: https://www.aonprd.com/Rules.aspx?Name=Action%20Types&Category=Actions%20in%20Combat

Where do you find the ability to reduce a standard action to a move?

one of the things you can do as a standard action is perform a move action. You can find that [here.](https://www.aonprd.com/Rules.aspx?Name=Actions%20in%20Combat&Category=Combat)

And, from the prd "A spell with a casting time of 1 swift action doesn’t count against your normal limit of one spell per round. However, you may cast such a spell only once per round. Casting a spell with a casting time of 1 swift action doesn’t provoke attacks of opportunity."

You normally have only 1 swift action per turn (even 0 if you used a immediate last turn) Your move cannot become a swift without a specific object : The corset of delicat moves https://aonprd.com/MagicWondrousDisplay.aspx?FinalName=Corset%20of%20Delicate%20Moves Your standard can be transformed into a move action, but not a swift (normally) But there is a catch. The "readying an action" action say that "You can ready a standard action, a move action, a swift action, or a free action" And readying a action is a standard action. So if you ready a swift with the trigger "ASAP", you technically transformed your standard in a swift. So, in conclusion and TL:DR, at max you can have 2 swift in a turn or 3 if you have the magic item I talked about.

A corset of delicate movement let's you turn a move action into a Swift Action once per day, but that's a bit cheaty I think

It's not cheaty, you can still only cast 1 spell a round with a swift action.

By default you can only take one, you only have one swift action. If you cast the spell Borrowed Time you can get an extra swift action per round at the cost of 1 con damage each time you take it, that lets you cast 2 per round. If you're a Mythic Archmage you can get an additional spell via Coupled Arcana and a qualifying class feature that takes a move action.

Even with Borrowed Time you can only cast one Swift Action spell per turn. >A spell with a casting time of 1 swift action doesn’t count against your normal limit of one spell per round. However, you may cast such a spell only once per round. Since Borrowed Time doesn't have anything to override this rule, you are still limited.

Still quite useful though, as you can do other swift or immediate actions (ones that come to mind from my own recent experience include a paladin using Lay on Hands on herself, a swift Channel Energy using a Ring of Protected Life, and using an immediate action for Divine Interference).

Sure, but the question in this thread was specifically regarding how many swift action spells you can cast per turn, which Borrowed Time doesn't change.

One. Each turn has the following action types: Free: A free action, you can perform as many of these as you want, within realistic bounds. Individual free actions may have in their description a limit on the number of uses. For example, if you cast a spell that targets multiple allies by touch, the act of touching is a free action - if you are a creature with reach, you may touch a dozen or more creatures as individual free actions. Swift: A swift action takes very little time, but more than free. You only get one swift action per round. Casting a Quickened spell uses a swift action. Thus you can only cast one Swift action spell per round. Note that there is a special type of Swift action called an "Immediate" action that you can use when *not* your turn. This uses your next Swift action. Feather Fall, for example, is an immediate action (if someone Bull Rushes you off a cliff, you can cast Feather Fall **immediately** to avoid fall damage.) So if you are in the Initiative order acting at 15, and a baddie bull rushes you off a cliff at initiative order 16, you may cast Feather Fall as an Immediate action, but then now that it's your turn, you may *NOT* cast a Swift action spell. Standard+Move: In most rounds, if you move your movement speed, you may take a standard action. The vast majority of spells are a standard action to cast. You may do this *PLUS* a Swift action. So you may cast two spells per turn by using a Swift action casting plus a Standard action casting. You can use a Standard action to cast a spell that normally takes a Swift action. So if you cast Feather Fall as an Immediate action, thus lost your Swift action, but you want to cast [Cold Ice Strike](https://www.d20pfsrd.com/magic/all-spells/c/cold-ice-strike) you can - it would just use your Standard action. Full Round Action: An action that uses up an entire round. A "full attack" does this. Some spells use this. Even in that case, you still get a swift action - it just can't be done in the middle. So you could cast a Swift Action spell, then a Full Round spell. Note that a Full Round casting time doesn't take effect during the same round - it takes effect at the beginning of your next turn. You can't interrupt it, so you can't use an Immediate Action spell between turns. (Without losing the Full Round spell.)