Retail planning, explained
What is weeks of cover?
Weeks of cover is how long the stock you hold will last at a given rate of sale: stock divided by weekly sales. It reads like a stock figure, but only half of it is counted. The stock is a fact. The rate of sale is a choice, taken from the weeks just gone or the weeks to come, and most of the ways cover misleads come from forgetting which one went in.
This guide covers the arithmetic, forward and backward cover, the 4 traps that skew the figure and what good cover looks like by category type.
6 min read · Updated 21 October 2026
The basics
Cover turns units into time.
600 units tells you very little on its own. At 10 a week it is more than a year of stock. At 300 a week it is gone by the weekend. Cover fixes that by expressing the holding in the unit every line shares: weeks of selling.
That is why the trade meeting runs on it. It puts a fast line and a slow one, a big store and a small one, March and November, on a single scale. Low cover says buy, chase or move stock in. High cover says stop sending, move stock out or look at price.
It can be counted in units or in value. Units suits a line or a store. Value suits a category, where units at different prices do not add up. The arithmetic is the same.
The calculation
The arithmetic is a single division.
Weeks of cover = stock ÷ weekly rate of sale.
Take the 600 units in one store. Over the last 4 weeks the line sold 80, 90, 100 and 130 units: 400 in total, an average of 100 a week. 600 divided by 100 is 6.0 weeks of cover.
- 600
- Units on hand, counted
- 6.0
- Weeks of cover at 100 a week
The 600 is a count: somebody can walk into the stockroom and check it. The 6.0 is that count divided by an assumption, that the next 6 weeks will sell like the last 4. Nothing in the figure says so.
Forward and backward
Forward cover answers the real question.
Backward cover divides by what has already sold, usually the average of the last 2 to 4 weeks. It needs no forecast and describes the past accurately. Forward cover divides by what is expected to sell, and answers the question the meeting is really asking: when does this run out?
The same 600 units, read forward. The line is building, and the next 5 weeks are expected to sell 120, 140, 150, 150 and 90.
| Week | Expected sales | Stock at end of week |
|---|---|---|
| 1 | 120 | 480 |
| 2 | 140 | 340 |
| 3 | 150 | 190 |
| 4 | 150 | 40 |
| 5 | 90 | 0, sold out partway through |
The 40 units left after week 4 last 40 ÷ 90 of week 5, so forward cover is 4.4 weeks. The shortcut, stock divided by the average of the next 4 weeks, gives 600 ÷ 140, or 4.3. Either way, the backward 6.0 promised 1.6 weeks the shelf will not have.
- 6.0
- Weeks of cover, backward
- 4.4
- Weeks of cover, forward
Backward cover is still worth reading as the check on the demand forecast. When the two are far apart, either the line is changing pace or the forecast is wrong. Both are worth knowing before anyone orders.
4 traps
Most traps live in the denominator.
The stock in the sum is rarely the problem. The rate it is divided by, and what gets counted alongside the stock, is where cover goes wrong.
- In-transit units.
- Add 200 units landing in week 3 and the line looks like 800 units of cover, about 1.4 weeks more at 140 a week. Those units do nothing for a shelf that empties first. Cover on hand answers "do we run out before the delivery?" Cover with in-transit answers "do we need to order more?" Both are right. Say which one you mean.
- Promotional weeks.
- The 130 in the example's last week was a promotion. Leave it in and the rate is 100, for 6.0 weeks. Take it out and the rate is 90, for 6.7. A promotion in the history makes cover look shorter than it is and invites a chase nobody needs. A promotion in the weeks ahead does the opposite, so forward cover has to include it.
- Size-level cover.
- A style can show 6 weeks while its best size shows 1. Size 12 holding 30 units and selling 25 a week has 1.2 weeks, and the store trades as if it is out of stock while the style total looks fine. Cover read only at style level hides the broken size until it is too late to replenish.
- Seasonal products.
- A coat holding 1,000 units in early October, after a September selling 20 a week, has 50 weeks of backward cover. With November expected at 120 a week, forward cover is about 8. At the other end of the season, cover that runs past the last selling week is not cover. It is next season's markdown.
What good looks like
Good cover depends on what you sell.
There is no single right number. A figure borrowed from another retailer brings their lead times and their customers with it. Good cover bridges the gap the line actually has to bridge, and that gap changes by category type.
| Category type | What cover has to bridge | Where it should finish |
|---|---|---|
| Continuity lines | Supplier lead time, plus the review period, plus safety stock for the swings | Never at zero. A steady level, topped up |
| Seasonal and fashion | The weeks left in the selling window | Close to zero on the last selling week, by design |
| Short shelf life | Sales before the stock expires | Always shorter than the shelf life |
| Long-lead imports | The time until the next delivery can land | Above that gap until the next delivery arrives |
| New lines | The time until real sales replace the forecast | Short in stores, with depth held back centrally |
For a continuity line the sum is direct. A 6-week lead time, reviewed weekly, needs at least 7 weeks of forward cover when the order is raised, plus the safety stock the line's swings ask for. Anything less runs out before the order lands.
Too much cover costs too. Every surplus week is cash the business cannot buy with, which is why high cover and a tight open-to-buy tend to turn up in the same place.
In merchmix
merchmix keeps cover live.
In core, stock cover sits beside availability, overstock and understock for every style, product, store and merchandise week, and it is live in seconds. The figure in the meeting is the one on the screen, not the one from the last rebuild of the sheet. See inventory management.
The traps are read where they happen. Size analysis reads stock cover and incoming stock by size, so a broken size shows before the style total moves. Allocation and replenishment use weeks of cover, in-transit units, target stock levels and safety stock to recommend store quantities, so stock already on its way is counted before more is sent. See allocation and replenishment.
When one store runs short of cover and another runs long, yukti drafts the rebalance or the refill. You approve it, or let it run.
Drag the growth on last year below. The stock on hand and on order does not move. The cover held does.
Your cover, on your own data.
Questions, answered.
What is weeks of cover?
Weeks of cover is how long the stock you hold will last at a given rate of sale. It is stock divided by weekly sales, in units or in value.
How do you calculate weeks of cover?
Divide stock by the weekly rate of sale. 600 units selling 100 a week is 6.0 weeks of cover. The rate can be the average of recent weeks (backward cover) or the expected sales of the coming weeks (forward cover).
What is the difference between forward and backward cover?
Backward cover uses the sales that have already happened. Forward cover uses the sales expected next, and answers when the stock will actually run out. When a line is speeding up or slowing down, the two can be weeks apart.
Should weeks of cover include stock in transit?
It depends on the question. Cover on hand tells you whether the shelf lasts until the delivery lands. Cover including in-transit and on-order stock tells you whether you need to buy more. Both are valid, as long as everyone in the meeting knows which one is on the screen.
How many weeks of cover should I hold?
Enough to bridge the gap the line has to bridge: lead time plus review period plus safety stock for continuity lines, the remaining selling weeks for seasonal lines, less than the shelf life for anything that expires. A number borrowed from another business brings its lead times with it.
Is weeks of cover the same as weeks of supply?
Usually, yes. Weeks of supply, stock cover and weeks on hand describe the same sum. Some teams use days of cover for fast-moving lines, which is the same division with a daily rate.
What does high weeks of cover mean?
More stock than the expected rate of sale needs. On a seasonal line, any cover that runs past the end of the selling window is likely to end in a markdown. On a continuity line, it is cash tied up that the open-to-buy cannot spend.
Why is weeks of cover different at size level?
Because sizes sell at different rates. A style can show 6 weeks of cover while its best size has 1, and the store trades as if it is out of stock. Size-level cover is what allocation and replenishment should read. In core plus, both work with size curves and size overrides alongside weeks of cover.
Now you can argue with the figure.
merchmix shows cover by style, store and size, live in seconds. See it in a demo, or try it free for 6 weeks on your own data.