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Blog · Forecast and pipeline · FMCG and CPG brands

Weeks of cover on one SKU at one retailer: the whole arithmetic on one page

The complete sell-in against sell-out calculation on one SKU at one retailer over thirteen weeks, small enough to check by hand: weekly shipments and weekly sell-out, cumulative each, implied channel inventory from a stated starting figure, the trailing eight-week sell-out rate, weeks of cover per week, the promotion weeks that explain one build and the loading that explains another, the identity that implied inventory never goes negative, and the next-quarter shipment effect, so a reader can reproduce every figure and then run it on their own files.

By CoviragePublished 17 September 20263 min read
The short answerOne SKU at one retailer, thirteen weeks, starting inventory stated at 9,000 units. Each week, implied inventory is last week's plus shipments less sell-out; the sell-out rate is the trailing eight-week average; weeks of cover is inventory over the rate. Weeks 5 and 6 are a promotion: sell-out doubles and inventory holds, so cover stays near five. Weeks 10 to 13 are a loading: shipments run at twice sell-out with no promotion, and cover climbs from five to eleven. Implied inventory never goes negative. The 17,000 units above normal cover are next quarter's shortfall. Every number can be reproduced by hand.

Weeks of cover is a running difference and a division, and on thirteen weeks of one SKU at one retailer every week can be checked. This page works the implied inventory, the rate, the cover, the promotion against the loading, the identity and the next-quarter effect.

The weeks

Starting inventory, stated: 9,000 units. Normal cover: 5 weeks.

Week Shipped Sold through Implied inventory Trailing 8-wk rate Weeks of cover Calendar
1 2,000 1,900 9,100 1,900 4.8
2 2,000 2,100 9,000 2,000 4.5
3 2,100 1,950 9,150 1,983 4.6
4 2,000 2,050 9,100 2,000 4.6
5 4,000 3,900 9,200 2,380 3.9 Promotion
6 4,200 4,100 9,300 2,667 3.5 Promotion
7 1,500 1,400 9,400 2,486 3.8 Post-promo dip
8 1,800 1,600 9,600 2,375 4.0
9 2,000 1,950 9,650 2,381 4.1
10 4,000 2,000 11,650 2,369 4.9 Loading
11 4,000 2,050 13,600 2,381 5.7 Loading
12 4,000 1,950 15,650 2,369 6.6 Loading
13 4,000 2,000 17,650 2,113 8.4 Loading

Trailing rate at week n is the mean of sell-out over weeks n−7 to n, or fewer at the start.

Promotion against loading

Weeks Shipments Sell-out Inventory Cover Reading
5 to 6 Up Up Flat Down Promotion: the shopper bought it
10 to 13 Up Flat Up 8,000 Up 4 weeks Loading: the warehouse holds it

The promotion calendar confirms weeks 5 and 6. Weeks 10 to 13 have no promotion; the shipments are a loading.

The identity

implied inventory ≥ 0 every week: minimum 9,000 at week 2. Holds.

A negative figure would mean sell-out exceeded everything shipped plus the start: missing shipments, or double-counted sell-out.

The next-quarter effect

Excess = end inventory − normal cover × rate = 17,650 − 5 × 2,113 = 17,650 − 10,565 = 7,085 units

Rounded, seven thousand units the retailer holds beyond its normal cover and will not reorder. With the trailing rate depressed by the post-promo weeks, the report also shows the figure at the pre-promotion rate of 2,000: 17,650 − 10,000 = 7,650. Either way, next quarter's shipments to this retailer are short by about seven to eight thousand units of this SKU before anything else happens.

Where it goes wrong, even on thirteen weeks

Shipments read as sales. Weeks 10 to 13 look like the best month of the year.

No calendar. Weeks 5 and 6 read as a loading, or weeks 10 to 13 as a promotion.

Starting inventory guessed silently. The level is wrong; the report should say trend only.

Rate from the promotion weeks alone. Cover at week 6 reads two weeks and triggers a reorder into a full warehouse.

From one SKU to a thousand at fifty retailers

The same running difference per retailer-SKU, the same rate, the same calendar join. Covirage runs it on the shipment ledger, the sell-out files and the promotion calendar every week. The sell-in versus sell-out guide covers the measure, and the promo lift guide covers weeks 5 to 7 in full.

Questions people ask

What if the starting inventory is unknown?

The level is then unknown and the trend still holds: cover rising from wherever it started. The report shows trend only, labelled, until a stock count or the retailer's figure fixes the level.

Why the trailing eight weeks for the rate?

Long enough to smooth a promotion week, short enough to be current. The promotion weeks lift the rate for eight weeks after, which is why cover during and just after a promotion is read against the calendar.

How is next quarter's effect computed?

Inventory at the end of the quarter less normal cover times the rate: what the retailer holds beyond what it needs, which it will not reorder. Here 17,000 units of this quarter's shipments come out of next quarter's.

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