As others have said, it is 50% per contract.
And although it seems like a distinction without a difference, it DOES matter. Because if you've used more than 50% of the points in one contract already, you can only borrow what's left and can't make up the difference by borrowing more than 50% from another contract.
Example:
Contract #1 = 100 points (75 points are already "spoken for" because of reservations that fall next UY, 25 points remaining)
Contract #2 = 100 points (all 100 points available in next UY)
You can borrow up to 50% per contract, but contract #1 only has 25 points available to borrow. So, instead of being able to borrow 100 points (50% of your total points for both contracts), you can only borrow 75 points (25 points from contract #1 because that's all that's left, and 50 points from contract #2 because you can only borrow 50% of each contract).