Need computation breakdown

[jmcph]

Need Help! I wish to compute for Principal and Interest. My computation is relatively simple, Interest will be computed only if total collection EXCEEDS the loan amount. 

My sample data are: 

For the month of March

cummulative collection of 6,920 is LESS than Cummulative loan amount, so the collection of 5,770 is purely PRINCIPAL

For the following month (April)

cummulative collection exceeds the cummulative loan amount, thus the current month collection of 5,080 should be divided into

2,000 Interest

3,080 Principal

How should i formulate my PRINCIPAL and INTEREST measure to achieve my desired output?? 

Any help will do. Thank you

[amitchandak · Accepted solution]

@jmcph ,New measure assuming other are measure

Principal= if( [cummulative collection] >  [cummulative loan amount], [collection] - ([cummulative collection] - [cummulative loan amount]) , blank())

Interest = if( [cummulative collection] >  [cummulative loan amount], ([cummulative collection] - [cummulative loan amount]) , blank())

for else part I have used blank, but you can use other formula