I am trying to replicate a built-in function in our application that calculates Days Forward Coverage (How many days can your supply fulfill demands in a given horizon).

I know how to arrive at the desired result which is by manually counting the number of days and now I am trying to figure out what the formula would be to get to the desired result based on the data below.

Current Inventory Total Demand Total Supply Horizon
523,843 1,442,280 1,643,843 361 days

The built-in function that we have shows that the Current Inventory would be able to fulfill future demands for the next 82.81 days.

I'm trying to find what would be the formula that could get me 82.81 days, but no luck so far and I've been stuck on this problem for a week now.

  • $\begingroup$ On the surface, it doesn't look as if we have enough information here. What is "Total Supply", say, as opposed to "Inventory"? Is there a way to meet Demand that doesn't draw from Inventory? And, more directly to the point, how long will unmet Demand wait? Presumably the authors of this app have a lot of history to draw from, but we have none. $\endgroup$
    – lulu
    Nov 9, 2022 at 11:56
  • $\begingroup$ My apologies. The Total supply is the Current Inventory + all the supplies that would come within the given horizon. All Demands would be deducted from the Current Inventory. It doesn't really matter how long a Demand has to wait before it could be fulfilled. $\endgroup$
    – Brilight
    Nov 9, 2022 at 12:39
  • $\begingroup$ Well then, the rate at which "Supply" is converted to "Inventory" is critical. If $100\%$ of Supply is instantly converted to Inventory, you have more than enough to meet all of the Demand. So, presumably, the issue is that it takes time to create more Inventory. $\endgroup$
    – lulu
    Nov 9, 2022 at 12:44
  • $\begingroup$ Cheap observation: Current inventory is a bit more than $36\%$ of Demand, so if we spread Demand uniformly over the year, you could meet demand for about $131$ days without converting anything from Supply. So...somehow you are heavily frontloading demand (which is why I asked if Demand had some kind of time stamp on it). $\endgroup$
    – lulu
    Nov 9, 2022 at 12:53
  • $\begingroup$ Yes, the Demands fall on different days across the given horizon. We can see that the current Inventory of 523,843 can only cover the demands for the next 82.81 days (which has a total demand of 526,008) and the next 277 days has a total demand of 916,272. $\endgroup$
    – Brilight
    Nov 9, 2022 at 13:00


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