The daily allowance calculator can be accessed in two different places.
For version 3.7.0 and newer, on the iPhone go to the 'More Tab' and locate the Daily Goal Calculator.
and then choose 'Daily Goal Calculator' (this option can also be found on the left side menu on the iPad).
Alternatively go the calculator tab and choose the appropriate calculator.
For older versions of the app.
First place is go to the 'More' tab and choose Daily Allowance Calculator
Or secondly go to the calculators tab and choose the daily allowance calculator for the standard iPhone switch.