I wanted to buy Mega spool of Seaguar Fluorocarbon and I wonder if it has shelf life, so I need to buy smaller spool, if not ill buy biggest spool.

Tackle shops use 5,000 yards spools to make money re spool  reels by the yard. IMO you are better buying 600 yard spools on sale twice a year during sales. 

Tom

If stored properly I think the shelf life is virtually unlimited.

Some of my reels have fluorocarbon that is over a year old.  I have boxes that have been in my bait cabinet for years.  It’s all good.  I even have a spool of mono that is over 5 years old and still good.

 

As stated above, if stored cool, dry, and dark it should last indefinitely. I still have almost 3,000yds of Pline Tactical filler spools from the BOGO sale TW had several years ago.  

2 hours ago, Jig Man said:I even have a spool of mono that is over 5 years old and still good.

 

I have some big spools of Big Game from the 90’s I found in the back of a cabinet. I’m tempted to use it but it would just be my luck to hook my PB and then find out it’s no good

I've used Tatsu on a reel for over 4 years, and Invisx for more than 5.  I'm sure you'll be good.  I've got some on a big spool that is three years old, and have no second thoughts about using it to spool up some new reels.

The big 5,000 yard spools have large diameter arbors to reduce cold flow pressure deforming line. The question to ask yourself is would you want your reel spooled with old line off the bottom of the filler spool?

Tom

Sure sells more line if you promote the idea that line expires in a week.   Wouldn't it be great if plastic biodegrade that fast.

 

As with any plastic, store it properly at room temperature and you'll be fine for a long long time.  Not that hard to do.  Leave it in 100+ degrees heat, exposed to UV and weather and you will have problems with most everything.  I worry more about and take more care of my cigars and whisky than with fishing tackle.

FC has much higher thermal and UV tolerance then Nylon mono that needs UV inhibitors added to protect it.

Mono line needs to be kept under 105 f and above freezing temps away from sunlight, FC doesn’t.

Tom