When configuring an additional fee on Stays.net, in the [Set an amount] field, you will be able to set the fee calculation model as shown in the image below:

Check out below what each option means:

Per night
This option makes the fee created variable depending on the length of the guest's stay, that is, the amount of the fee will be multiplied by the number of nights of the reservation.
Some OTAs accept only a single fee. So, in case you choose this option in your system, it will be applied only to your website.
Per reservation
It is the most common option regarding additional fees.
A single amount is charged, regardless of the length of stay or other variables.
Per guest and nights In this option the amount varies according to the number of guests and to the total of nights of the reservation.
The calculation is done as follows: the amount of the fee is calculated in relation to the guests and the result will be multiplied by the number of nights.
Fee = (amount of the fee  X number of guests) X number of nights.

For percentage fees, the base amount for calculating will always be the original daily rates total, that is, without application of other fees!

Now that you already know how the fee calculation models are available on Stays.net, how about checking out more related subjects?