Calculate payment over/shortage

[RusselB]

IN the attached spreadsheet, in column F there is a calculation for the minimum payment due in the following month.
What I've having difficulty with is calculating the amount paid up to and including the 20th day of that month, and then comparing that to the amount that was supposed to be paid, showing what, if any, overage or shortage in payment occurred.
I'd like this in column G.
Since the dates and amounts seemed relevant to solving this, I didn't anonymize that data.

My preference is a solution for OpenOffice, though I do have both Open and LibreOffice installed.

[MrProgrammer]

What I've having difficulty with is calculating the amount paid up to and including the 20th day of that month, and then comparing that to the amount that was supposed to be paid, showing what, if any, overage or shortage in payment occurred.

I don't fully understand how one knows which amounts to include. If it's the amounts in the period to the following 20th of the month =DATE(YEAR(A3);MONTH(A3)+(DAY(A3)>=20);20) and extending back one month =DATE(YEAR(A3);MONTH(A3)+(DAY(A3)>=20)-1;21), based on the date in column A, I'd create auxilllary columns to hold those dates. Then you can use SUMPRODUCT to sum the amounts in (I suppose) column E ($E$3:$E$201) between those dates. You can include a SUMPRODUCT term to restrict the selection to lines with description "xxxxxx xxx" if that's required for your calculation.
[Tutorial] The SUMPRODUCT function

I do not understand from your attachment how one would know "the amount that was supposed to be paid".

[RusselB]

The amount to be paid would, initially, be the amount shown for minimum payment.
The time period would be from the 21st of the previous month up to and including the 20th of the current billing month.
ie: Sum of negative amounts in E from Jan 21 to Feb 20 would be allocated to the amount in column F with the date of Jan. 26
The date discrepancy is due to processing time by the company.

For my purposes, just seeing if the minimum payment was matched, exceeded or short on a month by month basis, with the start of the month being the same date as that in column A that also has an entry in column F
While that doesn't match the companies processing times exactly, I can work with the discrepancy.