Formula for amount on previous month based on current month

I'm asking for the best probable formula for my ageing account, for example,

DATE ENTITY INVOICE AMOUNT
23-Nov-13 Entity 1 Invoice 1 3,315.66
23-Nov-13 Entity 2 Invoice 2 11,532.65
12-Dec-13 Entity 3 Invoice 3 2,524.50
6-Jan-14 Entity 4 Invoice 4 2,000.34
6-Jan-14 Entity 5 Invoice 5 3,349.28
6-Jan-14 Entity 6 Invoice 6 1,072.59
13-Jan-14 Entity 7 Invoice 7 6,697.69
13-Jan-14 Entity 8 Invoice 8 10,626.12
13-Jan-14 Entity 9 Invoice 9 2,148.61
6-Feb-14 Entity 10 Invoice 10 3,349.28
8-Feb-14 Entity 11 Invoice 11 4,494.06
8-Feb-14 Entity 12 Invoice 12 3,383.84

< 30 DAYS 31 - 60 DAYS > 61 DAYS
? ?? ???
what would be the best formula to compute the amount from previous months that would automatically update, in addition to Alt+= then click the amount. Thank you.

To Sixthsense Forum Guru,

Thanks but quite bit close. The analysis came FALSE..Our current date is February 21, 2014 and I need the amount that is over 60 days (Dec. 2013 downwards - 17,372.81); 31 - 60 days (month of January 2014 - 25,894.63) Less than 30 days (month of February - 11,227.18), and will automatically update as time goes by. Please help..

Many thanks and regards

So this isn't as elegant as a single formula, but you can hide the extra column if needed. It should update based on today's date.

To cffndncr,

Thanks, I think this might help a little bit.

Best regards

I do what I can