Free tool
Weeks of supply calculator
Enter on-hand units and average weekly sales to get weeks of supply, days of supply and a projected run-out date.
Your stock and sales
Estimated weeks of supply
8 weeks
- On hand (incl. on order)
- 1,200 units
- Days of supply
- 56 days
- Projected run-out date
- in 56 days
- Versus target
- +300 units
Positive means you are carrying more than the target weeks of cover; negative means less.
The formula
Weeks of supply = (on hand [+ on order]) ÷ average weekly sales
Days of supply = weeks of supply × 7
Excess or shortfall = (weeks of supply − target) × average weekly sales
- On-hand units
- Units in stock right now.
- Average weekly sales
- A trailing average of units sold per week, or a forward forecast for a seasonal or promoted item.
- On-order units
- Units already ordered but not yet received, included only when the toggle is on.
- Target weeks of supply
- The cover you are aiming to hold, to compare against what you have.
Worked example
- A warehouse holds 1,200 units and sells an average of 150 units a week, so weeks of supply is 1,200 ÷ 150 = 8 weeks.
- Days of supply is that figure × 7: 8 × 7 = 56 days.
- Against a 6-week target, the variance is (8 − 6) × 150 = 300 units above target.
When it applies
- Steady sellers, where a trailing average of weekly sales is a fair stand-in for the weeks ahead.
- Comparing cover across SKUs or categories on one consistent unit, weeks, regardless of price or unit cost.
- Flagging excess stock or an approaching stockout against a target you set for the category.
When it breaks down
- Seasonal or promoted items, where trailing sales misstate the weeks ahead; use a forward forecast in the average weekly sales field instead.
- SKUs that stock out often, since lost sales during the stockout hide real demand and understate the sales rate feeding the calculation.
- Cover looked at on its own, without lead time and safety stock: weeks of supply says how long stock lasts, not whether a reorder will land in time.
Common mistakes
Using a trailing average that includes stockout weeks
Weeks with no stock to sell pull the average down, which then overstates weeks of supply on the very item that most needs a reorder.
Comparing weeks of supply to lead time without adding safety stock
Lead time is how long a reorder takes to arrive; weeks of supply is only cover, not a margin for demand or delivery running long. Safety stock is what covers that gap.
Mixing units and dollars
On-hand entered in dollars against a sales rate in units, or the reverse, produces a ratio that is not weeks of anything. Keep both sides of the formula in the same unit.
Questions
What is the formula for weeks of supply?
Weeks of supply = on-hand units (plus on-order units, if included) ÷ average weekly sales. 1,200 units on hand against 150 units sold per week is 8.0 weeks of supply.
How is weeks of supply calculated?
Divide the units you have (on hand, and on order if you count it) by your average weekly sales rate. The result is how many weeks that stock covers at the current sales pace.
Weeks of supply vs weeks on hand?
They are the same measure under two names. Both divide available units by the weekly sales rate to say how many weeks of cover remain.
How many weeks of supply should I carry?
Enough to cover your supplier's lead time, plus a safety-stock cushion for how much demand and lead time vary. There is no single right number across items; size it per SKU with the safety stock calculator rather than picking one target for everything.
What is the difference between weeks of supply and days of supply?
Days of supply is weeks of supply × 7: the same cover, expressed in days instead of weeks. It is the more convenient unit when a supplier quotes lead time in days.
Related
Published by Skuvelo. Results are estimates computed from the figures you enter, not a reading of your own sales or stock.
A calculator answers once. Skuvelo keeps answering.
This tool computes one number from what you type. Skuvelo computes it continuously, for every SKU, from your own sales and stock.