Margin funding is calculated based on the amount, interest rate, and the number of seconds that funding was provided/taken.
Margin funding interest to pay:
Please note, if a user reserves and returns funds within an hour without using them, then they will pay a full hour’s interest.
Margin funding interest earnings:
The provider of funding will receive the interest paid by the user borrowing, minus a 15% fee.
For instance, if you have an active $10,000 USD offer at 0.06% you would earn $6.00 USD per day. On those $6.00 USD a 15% fee is charged, so $0.90 USD. You will receive $5.10 USD per day that the offer is taken.
Bitfinex will charge a minimum of one hour's interest to the borrower on any funding that is borrowed and subsequently returned without being used in a financed position.
The user that has provided the funding will receive the full hour earnings, minus a 15% fee.
If you have any questions contact the support team for further explanations, by providing as much information as you believe is relevant.