Zero! Hosts are paid 100% of the price they set for the experience.
Eatwith guests pay a 20% service fee covering the booking processing fee, advertising, insurance, and Eatwith support. This is added to the amount you indicate you will charge for the experience. For example, if you have entered $20 as the price for your experience, when a guest books, they will pay $24 ($20 + $4 (20% of 20)).