Revenue for a given period for a mobile app is simply a full income before Apple Tax (15% or 30% cut).
How to calculate Revenue?
It can be done in three ways:
Via App Store Connect dashboard. Go to your account and then refer to Sales and Trends tab.
Via Apple Sales Reports. It's a technical report which you can download in CSV and then analyze.
Via raw transaction events. This is the most accurate option which works on a user level. Get all information about users' transactions, sum all revenue and subtract re refunds. You'll get more detailed analytics including revenue source and attribution, currency and more.
For Android, it works in the same way only with Google Play Console.
How Adapty helps?
Adapty automatically calculates Revenue from raw transactions. Get all the information about metrics on a user and events level without a single line of server coding. And it works for all platforms.