Days to sell inventory: how to calculate it
Days to sell inventory is the number of calendar days between buying a resale item and selling it. Measure it for one item, or average it across the items you sold in a period to see how long your money stays in stock before a sale brings it back.
The figure shows how long cash stays tied up. It does not show whether a purchase was a good one, so read it next to the item's cost and fees. For the fee terms, see what is a resale fee.
How do you calculate days to sell for one item?
Days to sell equals the sale date minus the purchase date, counted in whole calendar days. Weekends count too, because the item is still in your stock over them.
For each item you want to measure:
- Find the purchase date on the deal the item came from.
- Find the sale date on the sale that included the item.
- Subtract the purchase date from the sale date.
How do you calculate inventory days for a period?
Days to sell for one item tells you about a single sale. To judge a whole period, use the days sales of inventory (DSI) formula, which compares the stock you hold with the cost of what you sold:
Inventory days equals average inventory cost divided by cost of goods sold, times the number of days in the period.
Average inventory cost is the stock cost at the start of the period plus the stock cost at the end, divided by two. Cost of goods sold is the purchase cost of the items you sold in the period. Use 365 days for a year, or the number of days in a shorter period such as 30 or 90.
Worked example
The numbers below are an example. Four resale items sold in the spring, and the days to sell come from each item's purchase and sale dates.
| Item | Purchased | Sold | Days to sell |
|---|---|---|---|
| Desk lamp | March 1 | March 12 | 11 |
| Cast iron pan | March 3 | April 2 | 30 |
| Film camera | March 10 | April 23 | 44 |
| Vintage radio | March 10 | June 22 | 104 |
The average is (11 + 30 + 44 + 104) divided by 4, which is 47.25 days. The median, the middle value once the four numbers are sorted, is (30 + 44) divided by 2, which is 37 days. The radio sold after 104 days and pulls the average up. Look at both numbers before you decide that a category moves slowly.
For a separate 90-day period, the stock cost 1,400 at the start and 1,600 at the end, and the items you sold cost 2,000. Average inventory is (1,400 + 1,600) divided by 2, which is 1,500. Inventory days are 1,500 divided by 2,000, times 90, which is 67.5 days.
How do you measure sell-through rate?
Sell-through rate is the share of the units you had available that sold in a period. It measures how much of the stock moved. Days to sell measures how long each sale took.
Sell-through rate equals units sold divided by units available, times 100. Units available is the stock on hand at the start of the period plus the units you bought during it.
Say you had 5 units on April 1, bought 3 more during April, and sold 4. Sell-through is 4 divided by 8, times 100, which is 50%. Dividing by only the 3 units bought in April gives about 133%, because it counts sales of older stock in the numerator and leaves that stock out of the denominator.
Leave returned units out of the sold count, because a returned unit is back in stock. Use the same dates for sales and purchases, so both counts cover the same window.
What to do with slow stock
Slow stock is any item that has waited well beyond the time your past sales usually took. Inventory aging, which counts how long each unit has been waiting, is the simplest way to find it. Work through the unsold items in this order:
- Filter for old stock. Open the inventory list and apply the 60-day or 90-day aging filter. It shows items that are still In Stock or Listed and were bought at least that many days ago.
- Compare the cost with the price you realistically expect. The profit formula in how to calculate resale profit shows what the item would return.
- Pick one action for each item: lower the price and relist it, return it if the source accepts returns, or remove it if it is damaged or no longer for sale.
- Update the status to match what you did, so the inventory totals stay right.
- Track the median days to sell for each category over time. A category that drifts upward deserves a closer look before you buy more of it.
The how to track resale inventory guide covers the monthly review in more detail.
What FlipKeep records and what it leaves to you
FlipKeep stores the dates this calculation needs. Each deal has a purchase date, each sale has a sale date, and an item marked as Listed can carry a listed date, which appears in the item's activity. FlipKeep does not calculate days to sell or sell-through rate.
To work out the figures yourself, use the aging filter to find old stock, then export the inventory CSV. Each row includes a purchase_date and a sold_date column, so the subtraction is one formula per row. For a spreadsheet layout, see the reseller inventory spreadsheet template.
These limits affect the numbers you get:
- The aging filter shows only items that are In Stock or Listed. Sold, returned, and removed items do not appear in it.
- Aging counts from the purchase date. The listed date is not in the CSV export.
- If an item sells, comes back, and sells again, the inventory CSV shows the latest sale date.
- The aging filter is read-only. Applying it does not change any record.
FlipKeep gives full access during a 30-day trial. After the trial, your existing records stay available to view, search, and export without a purchase. Adding purchases and sales, editing records, and iCloud continuity need full access. The trial includes it, and after the trial a one-time purchase gives full access.
Common questions
How do I calculate days to sell inventory?
Subtract the purchase date from the sale date for each item, counting whole calendar days. For a period, average the results across the items sold, and check the median too, since one slow item can move the average a long way.
What is a good number of days to sell?
There is no universal target. Compare each category with your own earlier results, because a seasonal item and an everyday item sell on different timelines.
Is sell-through rate the same as days to sell?
No. Sell-through rate is the share of available units that sold in a period. Days to sell is how long each sale took.
Does the aging filter include items that have sold?
No. The aging filter only shows items that are still In Stock or Listed.
Can FlipKeep show the days between listing and sale?
FlipKeep stores the listed date and shows it in an item's activity. It does not calculate the gap between listing and sale, and the CSV export does not include the listed date.
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