Financial Impact by Quarter weighted by the month?

[johncon60]

I've done calculations for financial impacts by year before - no big deal, but I was requested to dig a bit deeper. I have a list of customers with different end dates and products with varying % increases. So if I customer has a new contract starting in Apr. 2024, I can calculate 5% increase impact for the remaining 8 months. Not a problem. The powers that be, curse those powers, would like the impact by quarter - but scaled as accurately as possible. For example, an April start date, not a problem, 5% for 3 months for Q2. Column M has month, Column N has %. Columns P, Q, R, S have quarters 1-4. My issue is how do determine which quarter and the amount for a month that isn't the first of the quarter, ie, August for Q3? Or November for Q4? How do I determine the impact per the quarter but still weigh it by the months remaining in that quarter? Calculating months, no problem and quarters, no problem but to determine the impact part way through a quarter?