Weeks Of Supply Calculator

Work out weeks of supply instantly with clear inputs, formula shown and shareable results.

About Weeks Of Supply Calculator

Weeks of supply converts an inventory position into time at the current rate of sale, which is how retail buyers actually think. Including units on order is essential, because a comfortable on-hand position can conceal an incoming over-buy.

Formulas

Weeks of supply

WOS = Current inventory / Average weekly sales

Target inventory

Target units = Target weeks of supply x Average weekly sales

Worked example

With the default values below, Weeks Of Supply Calculator returns Weeks of supply on hand of 15.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Current inventory: 4,800
Average weekly sales: 320
Units on order: 1,200
Target weeks of supply: 12

Results

Weeks of supply on hand: 15.00
Weeks of supply including on order: 18.75
Inventory at the target weeks of supply: 3,840
Excess (+) or shortfall (-) against target: 2,160

Step by step

1Values used
2Weeks of supply
3Target inventory
4Weeks of supply on hand= 15.00
5Weeks of supply including on order= 18.75
6Inventory at the target weeks of supply= 3,840
7Excess (+) or shortfall (-) against target= 2,160

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What target is appropriate?

8-12 weeks for basics with reliable replenishment, 4-6 for fast fashion, and much higher for seasonal goods bought once ahead of season.

Why does it break down on new lines?

Because there is no sales history to divide by. Use a planned rate of sale until four to six weeks of actual data exist.