@Suzi2 Airbnb charges guests a separate fee apart from your 3%. This fee is added on top of your nightly rate, hence you cannot know the actual amount the guest pays. This added amount ranges between 6 - 12%
From the Airbnb help centre:
"The exact amount of the service fee is displayed before guests confirm a booking. Service fees for guests typically range between 6-12% but can be higher or lower depending on the specifics of the reservation. The higher the subtotal, the lower the percentage so you can save money when booking large reservations."
Sometimes Airbnb can also charge VAT, based on the local tax laws.