Binance will double referral commission rewards to 40% for all accounts that hold 500 BNB or more, starting from 2018/05/19 0:00 AM (UTC). Each user’s commission rate will then be adjusted at 0:00 AM (UTC) each day based on their BNB holdings. The commission rate for all other users will remain at 20%.
https://support.binance.com/hc/en-us/articles/360004047051-Binance-Doubles-Referral-Rewards