Bitfinex offers different fee tiers categorized by user’s 30-day volumes, which is calculated every 12 hours.
Your 30-day volume is a moving sum of all trades executed between the current time and the previous 30 days.
You are able to check your account’s fee tier by following the link below: https://www.bitfinex.com/reports/summary
The general fee range is found here: https://www.bitfinex.com/fees
In general, all orders are charged a maker or taker fee. Maker fees are paid when you add liquidity to our order book by placing a limit order under the ticker price for buy and above the ticker price for sell. Taker fees are paid when you remove liquidity from our order book by placing an order that is executed against an order of the order book.
A Post-Only Limit Order ensures that you will pay the maker fee and not the taker fee unless matched with a hidden order.
If after checking this, you believe you have been incorrectly charged contact us through our support channel, and provide us with the order ID, in question.