Average Weekly Sell Through Percentage Formula

If you sold a constant percentage of the inventory each week, then weekly sales would be decreasing as inventory decreased.

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	B	C	D
3	today's date	10/24/2018
4	markdown date	2/1/2019
5	weeks until markdown	14.3	C5: =(C4-C3)/7
6	targeted sell through %	75%
7	today inventory	10,000
8	ending inventory	2,500
9	average weekly sell through %	9.909%	C9: =1 - (C8/C7)^(1/(C5-1))

Oops; that should be ...

	B	C	D	E
3	today's date	10/24/2018
4	markdown date	2/1/2019
5	weeks until markdown	14.3		C5: =(C4-C3)/7
6	targeted sell through %	75%
7	today inventory	10,000
8	ending inventory	2,500
9	average weekly sell through %	9.248%		C9: =1 - (C8/C7)^(1/C5)
10
11	Week	Date	Inventory
12	0	10/24/2018	10000.0	D12: =C7
13	1	10/31/2018	9075.2	D13: =D12*(1-$C$9)
14	2	11/7/2018	8235.9
15	3	11/14/2018	7474.2
16	4	11/21/2018	6783.0
17	5	11/28/2018	6155.7
18	6	12/5/2018	5586.4
19	7	12/12/2018	5069.8
20	8	12/19/2018	4600.9
21	9	12/26/2018	4175.4
22	10	1/2/2019	3789.3
23	11	1/9/2019	3438.9
24	12	1/16/2019	3120.8
25	13	1/23/2019	2832.2
26	14	1/30/2019	2570.3
27	15	2/6/2019	2332.6

You're welcome.