Calculating Annual Contract Value - start date end date

[ballist1x]

Hi i am tyring to calculate the annual value of Contracts for example the total to be billed in 2018, 2019 etc

Acontract has a

Start Date: Format dd/mm/yy

End Date: Format dd/mm.yy

total value £

Monthly value£

if a contract has a monthly value of £100 and goes from 1/1/2017 to 31/6/2018

i want to be able to select a drop down filter that i can select, for example, 2017 and it returns £1,200 (12x months * £100)

Also, if i select on the drop down 2018 it would return the value £600 (6 months * £100)