How to sum a value for a certain period of time (certain number of months/years)

[muketaz]

Hi everyone! First of all I want to express my excitment for the brand new site, thank you to everyone who makes the growth of the community possible. 

My question is about calculatting fixed costs, amortization mainly.

I have a table of payments ("Pagos") in wich all the expenses are registered. Every time I buy a thing that has amortizable costs I complete the number of years that I will be paying that amortization, and calculates the monthly cost for that amount of years. 

Then I have this formula, to divide payments monthly: "Mes de pago": EOMONTH([Fecha pago], 0) 

I create a view and agroupates payments by "Mes de pago" and count for the total amount of payments, so I have something like this:

And the same view for fixed costs and variable costs. Is there a formula with I can sum the value of amortization since present month and for 24 months, only for that period.

I know its a little bit messy, but I can explain better if you have any question.

[Joseph_Seddik]

https://help.appsheet.com/en/articles/895302-slices-the-essentials