Retail Sell-Through Rate, Weeks of Supply (WOS) & Stock-to-Sales

Use one consistent inventory cohort and period

This example starts with B2 units available, sells B3 of those units during the selected period, and has no later receipts, returns, shrinkage or transfers. Ending stock is therefore B2-B3. If those movements exist, calculate ending stock from the inventory ledger instead.

Sell-through here means units sold divided by opening available units. The inverse is explicitly beginning-stock-to-period-sales; other stock-to-sales definitions use ending or average stock and are not interchangeable. Use the same units and reporting period.

Weeks of supply divides ending stock by a supplied average weekly sales rate. The rate may be fractional and is not a guaranteed demand forecast or reorder date. Zero weekly sales with stock remaining means no finite estimate, not proof of dead stock. Zero ending stock returns zero weeks, including when the observed sales rate is zero.

Sell-through of the opening inventory cohort

For this closed cohort the result lies between zero and one. With no opening stock, the ratio is undefined.

=IF(COUNT(B2:B4)<>3,"Invalid inputs",IF(OR(MIN(B2:B4)<0,B2<>INT(B2),B3<>INT(B3),B3>B2),"Invalid inputs",IF(B2=0,"N/A",ROUND(B3/B2,4))))

Remaining weeks of supply

Use the supplied weekly run rate for the same product and units. Do not infer permanent obsolescence from a zero rate.

=IF(COUNT(B2:B4)<>3,"Invalid inputs",IF(OR(MIN(B2:B4)<0,B2<>INT(B2),B3<>INT(B3),B3>B2),"Invalid inputs",IF(B2=B3,0,IF(B4=0,"No finite estimate",ROUND((B2-B3)/B4,2)))))

Beginning stock divided by period sales

This is the inverse of the stated sell-through when sales and opening stock are positive. With no sales, return N/A.

=IF(COUNT(B2:B4)<>3,"Invalid inputs",IF(OR(MIN(B2:B4)<0,B2<>INT(B2),B3<>INT(B3),B3>B2),"Invalid inputs",IF(B3=0,"N/A",ROUND(B2/B3,2))))

Further reading

• Microsoft Support — IF function