Calculated Tax - Percentage Value

Hello,
Yes, it is expected behavior.
“Calculated Tax” tax codes should be used on purchase-related items only (supplier invoice, purchase order etc.), as they support “reverse-charge” case - where both tax disbursed and received is reported by buyer. 
Effective tax rate on customer-related item (invoice/order) for such tax type is zero. 

if you carefully look on the screenshot you have shared, you can see that Domaine (Domain) for your code is set to Achat (Purchases).
 

Thank you, ​@Adam Bereda . The domain is a customization we added and it does not affect the standard behavior of IFS.

If a Calculated Tax is added to a Sales Object, is it expected that the tax rate will be 0%, even if a different rate is defined? (we do get 0% on sales and purchases objets)

Yes, that’s what I mentioned - Effective tax rate on customer-related item (invoice/order) for such tax type is zero. Tax will be reported by customer.

​@Adam Bereda  when i add the tax to a purchase order i still get a 0% instead of 20%

Again - it is as expected; Calculated tax does not increase value payable to supplier, it just generates two additional tax transactions - for tax disbursed and received to be presented in purchase tax register and sales tax register (tax payable and tax deductible)