Using 'if' in equation

I would like to perform a calculation on a field based on the value of another field e.g (if field 1>31, then set field 2=field +field 4, else set field 2=0). Is this possible?

Sorry for selecting potentially incorrect category. Typing this on my iPad, and I am unable to select any other topic choice below…

For anyone looking for how to do this...

http://helpdesk.knackhq.com/support/solutions/articles/5000443405-equations#conditionals