How do you calculate WIP day of supply?

WIP DOS is calculated (According to me) WIP in money divided by product material sales by day.

Take the previous weeks sales and divide by number of working days (Typically days on which products can be sold) normally 5 days per week.

Then divide WIP in money by Sales per working day from the previous week.

Not totally accurate but good enough.

You can use forceatsed sales for the following week but only if you have very accurate forecasts.

If you have only consumption based sales then use sales from the previous week.

You can use also previous months sales by must divide by working days in that month.