How it is computed
Count the units available for retail. Divide by the units retailed per day over the last thirty days. If the store sold sixty cars in thirty days, that is two a day; a lot of one hundred twenty units is sixty days of supply.
Why it matters
A unit count tells you how many cars you own. Days supply tells you whether that is too many. The same hundred units is a healthy lot for a store selling three a day and a problem for a store selling one.
It drives the buying decision. A desk that knows it holds ninety days of a segment stops buying that segment; a desk that only knows it owns thirty of them keeps buying.
How operators read it
- Run it by lane and by segment, not only for the store. A store at a comfortable total can be short on the trucks that sell and long on the sedans that do not.
- Read it against the market's days supply for the same vehicles. A unit the store has held sixty days in a market that turns it in thirty is a pricing conversation.
- Remember the denominator is a pace. A slow sales month raises days supply without a single car being bought, and the right response may be on the showroom floor, not the buying desk.
Questions people ask
What is the difference between days supply and inventory turn?
They are the same idea in two units. Turn says how many times a year the inventory sells through; days supply says how many days the current inventory would last. Three hundred sixty-five divided by one gives you the other.
Why thirty days?
Because it is short enough to reflect the current pace and long enough to smooth a slow week. Some stores run sixty and ninety alongside it to see the trend.
How A.D.A.M. reads it
A.D.A.M. computes days supply as units in stock over the trailing-thirty-day selling pace and reports it as unavailable, not as zero, when there was no demand to measure. He reads it beside the numbers it trades against, names what the gap is worth, and leaves the decision where it belongs. What an AI advisor should do, and refuse to do.