Days supply is one number that tells you everything about inventory health. Here's how to calculate it, segment it, and actually use it to make decisions.
Days supply is the answer to one question: "At my current sales pace, how many days would it take to sell every car on my lot?" It's a simple number. But it tells you almost everything you need to know about whether your inventory is healthy or toxic.
Get it right, and you have a tool that governs pricing decisions, stocking decisions, and acquisition strategy. Get it wrong, or ignore it, and you'll sit on aged inventory, tie up capital, and burn cash on carrying costs.
Here's how to calculate it, interpret it, and use it to actually move inventory.
Days supply is simple math:
Days Supply = (Total Units in Inventory / Average Daily Sales) × Days
Let's say you have 45 cars on the lot. Last month, you sold 30 cars across 30 days. That's 1 car per day on average. So your days supply is 45 days. It would take 45 days to sell out your current inventory at your historical sales pace.
If next month you have 45 cars and sell 2 cars per day, your days supply drops to 22.5 days. Same inventory. Faster sales. Lower days supply. That's the signal you want.
Most dealers calculate this number monthly or quarterly. That's too slow. Days supply should be a weekly or even daily number. Markets move fast. Your inventory aging rate changes week to week. You need current data to react.
Overall days supply is useful. But it's also useless by itself. Here's why: You might have 45 days supply overall, but that doesn't tell you about the composition of your inventory. You might have 20 days supply on SUVs but 80 days supply on sedans. Or 15 days supply on units under $15K but 60 days on units over $30K.
This is critical because different segments have different sales velocities. A popular sedan in your market might move in 20 days. A niche truck might take 60 days. If you're carrying too much of the slow segment, your overall days supply is artificially high—and your cash is stuck.
Smart dealers calculate days supply by:
When you segment like this, you see the real story. Maybe your overall days supply looks fine, but you're overstocked in trucks and understock in compact SUVs. Your allocation strategy is wrong. You need to fix it at acquisition, not wait six months to fix it with repricing.
The industry target is 30-45 days. This is the sweet spot. It means:
Some hot markets run 20-30 days. Sports cars, popular SUVs, in-demand colors and trims. These segments move fast. Days supply of 20 is fine because you're selling through quickly.
Slower segments or vintage colors might run 50-60 days. That's OK if it's intentional. You acquired them at a good price, and you're moving them at acceptable gross. But if you're at 80 days, you're holding too much dead weight.
The key is intentionality. Know why your days supply is what it is. Don't let it drift.
When days supply exceeds 60, money stops moving. Here's what happens:
The easiest way to kill a dealership isn't bad salespeople. It's a lot full of aged inventory and no capital to buy fresh stock. You're paying to store other people's cars while good deals drive past your gate.
Counterintuitively, days supply that's too low is also a problem. Below 20 days, you start running real risks:
The ideal is stability within the target range. 30-45 days. Enough selection. Enough velocity. Enough margin to be intentional.
Days supply is a pricing signal. Here's how to read it:
Segment days supply is 15-20: This segment is moving fast. You can hold price. Buyers want it. Margin is there. No need to discount.
Segment days supply is 30-40: This is healthy. Price is fair. A small discount ($300-500) could accelerate sales. Consider it if aged units are creeping in.
Segment days supply is 50-60: Getting long in the tooth. These cars need to move. A meaningful discount ($1,000-2,000) is justified. Repricing should be automatic.
Segment days supply is 60+: You're holding dead weight. Discount heavily ($2,500-4,000) or make an exit decision. At this point, the math says wholesale it. You'll recover more capital and kill the carrying costs.
This isn't guesswork. It's math. When days supply goes beyond your target, prices come down. It's not personal. It's inventory management.
Days supply should also govern what you buy. Here's the framework:
If segment days supply is below 20: You're understocked. This segment is moving faster than your supply. Buy more. Same body style, similar price band, similar model. Fill the gap.
If segment days supply is 30-45: You're at target. Buy selectively. New inventory should replace units sold, not expand the segment. Stay balanced.
If segment days supply is above 50: You're overstocked. Stop buying this segment. Don't acquire another sedan if you have 14 sedans aging on the lot. Let current inventory move first. Only new acquisition should be opportunistic (great deal, great unit, can price and move it fast).
This discipline prevents the death spiral. Too many dealers say "I'll buy whatever I find at auction." That's how you end up with 100+ days supply and a capital problem. Instead, let days supply guide acquisition. You'll turn inventory faster and deploy capital more efficiently.
Days supply and turn rate are related but different. Turn rate tells you how many times you sell your inventory in a year. Days supply tells you how long an average car sits.
If you have 50 cars and sell 10 per month, your annual sales are 120. Turn rate is 120/50 = 2.4 turns per year. Days supply is 50 cars / (10 cars per month / 30 days) = 150 days.
They measure the same thing from different angles. Days supply is more actionable for managers because it's in time units. "150 days" is more intuitive than "2.4 turns." Use whichever your team understands better. Just be consistent.
Here's what the best dealers do: Every Monday, they pull days supply data segmented by body style and price band. They look for segments that are creeping above target. Then they ask:
One Monday conversation beats four Fridays of crisis management. Days supply is your early warning system. Use it like one.
Calculating days supply manually is slow and error-prone. A good inventory management system calculates it automatically and segments it by the dimensions that matter to your business. You should see days supply updated daily, with trend lines showing whether each segment is improving or degrading.
The best systems also alert you when a segment exceeds threshold. 45 days? Alert. 60 days? Escalation. That automation is the only way to stay on top of it without hiring a full-time analyst.
Days supply is a number that tells you if you're buying right, pricing right, and stocking right. When it's 30-45 days and stable, you're doing your job. When it creeps above 60, you need to act fast. And when you segment it properly, it becomes a decision engine for acquisition, pricing, and movement strategy.
Calculate it. Segment it. Track it weekly. And let it govern your moves. That number will tell you more about your business than a hundred Excel sheets.
See days supply by body style, price band, and age. Get alerts when segments go above target. Make pricing and acquisition decisions with current data.
Book a Demo →Quick answers to the questions dealers ask most.
Days supply is the number of days it would take to sell every car on your lot at your current sales pace. The formula is total units in inventory divided by average daily sales. If you have 45 cars and sell one per day, your days supply is 45. It is the single number that tells you whether your inventory is healthy or backing up.
The industry target is 30 to 45 days. That range gives buyers enough selection without overloading capital or carrying costs. Hot segments like popular SUVs can run 20 to 30 days and still be fine. Anything above 60 means you are holding dead weight and need to act.
Weekly at minimum, daily if you can. Most dealers run the number monthly or quarterly, and that is too slow. Markets and aging rates move week to week, so a stale days supply number leaves you reacting instead of deciding. Pull it every Monday segmented by body style and price band.
Because the overall number hides where you are actually stuck. You might show 45 days supply overall but be sitting at 80 days on sedans and 20 on SUVs. Segment by body style, price band, age bucket, and CPO versus standard. That is how you find the segment that is eating your capital.
They measure the same thing from opposite angles. Turn rate tells you how many times you sell your inventory in a year. Days supply tells you how long the average car sits. A 2.4 turn rate equals about 150 days supply. Use whichever your team thinks in, just stay consistent.
Four things move days supply at a dealership. Your average daily sales velocity (the denominator), the current units in stock (the numerator), your segment mix (full-size trucks behave nothing like compact SUVs), and your price band (sub-$15k inventory typically turns 2 to 3 times faster than $35k+ units). Most dealers track the headline number and miss the segment story. Pull days supply broken down by body style and by price band every Monday. That is where the actionable signal lives.
Dealerships that win at stocking use days supply by segment as the decision filter. If a segment is below 20 days supply, the market is asking for more inventory there, so buy into it aggressively. If a segment is 30 to 45 days, you are at target, buy only to replace. If a segment is above 50 days, stop buying that category entirely until current units clear. The discipline is buying to the plan, not to whatever cheap deal walks through the auction lane that week.
Built and ran used car operations at the rooftop level before moving into training. Co-host of the LotTalk podcast and runs weekly 1-on-1 coaching with used car managers across hundreds of dealerships in the Lotpop client base. Specializes in the daily habits and process discipline that move turn rate from single digits into the 20s.
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