I have a problem with another trigger.

We have Opps with periods more than a month, usually, 6 or 12 months.
When I ran a report, it only gives me the total value of the opp for each month, how can i ran reports on specific months and only see the partial value for this specific period?

for example: Opp with period feb 2016 - jan 2017 total of 120 K€
my report period is for Q1 2016, so i want to see only 20 K€ (feb + mar 2016)