Help Needed: How to build formula? - CountIf(s), MRound, IndexMatch

[ReetzX]

Hi all.

I have the below forumula:
=IF(D3="";"Not Sold";(MROUND(D3-INDEX(AllRiskCars!G:G;MATCH('Sold Cars'!B3;AllRiskCars!A:A;0));30)/30)*INDEX(AllRiskCars!U:U;MATCH('Sold Cars'!B3;AllRiskCars!A:A;0)))

It's counting a "cost" where it set's a fixed amount every month - But it only needs to do this for a certain period (ex. 31/02-2018 - 31/02-2019, 12 Months)
When the period is passed it needs to take the last last possible amount (The highest) and put in when period is passed.

It needs to be with an index match, because the amount can be in between (200 - 500)

Is there any hardcore excel guy that can help me with this, or have any idea how this can maybe be build?

If you need anymore info please give a heads-up. :confused: