Admins! Is it possible to delete the redundant post (this one - without attachment)

Easiest way is to use a helper column. Attached is an example with different possible solutions:

You can define dynamic named range (dnDateMonth in my example), and use this to calculate the helper column DateMonth;
Or you can calculate month number directly in helper column - like in alternate helper column DateMonth2;
You can calculate current month like in named cell nCurrMonth, and use nCurrMonth in formula to calculate the amount for current month;
You can select the month using Data Validation List for cell nMonth, and use nMonth in formula to calculate the amount for selected month. You need a helper sheet (which can be hidden) to create a list of available months which is based on your date amount entries.