Executing IF THEN ELSE in Tableau

Question

I have the following graph:

I would like to calculate lapsed rate which is sum of lapsed value divided by sum of inforce value. I use the formula below in calculated field.

abs(sum(if[Status]='lapsed'then[TotalAmount]end))/abs(sum(if[Status]='inforce'then[TotalAmount]end))

However this formula also pick the value from Q2 (quarter 2) 2016.
What I want ?
First check if any quarter does not contain both inforce value and lapsed value then skip that quarter.
In this case I need to calculate lapsed rate which does not include Q2 2016. Can someone help me on how can i do it?