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Multi-Location Days of Supply Calculator

Enter your total on-hand inventory and total daily demand.

How it is calculated

The tool takes two totals, not a list of sites, so you add the locations up first. days of supply = total on-hand units / total daily demand and weeks = days / 7. Inventory is in units and demand is in units per day, so the result is in days. Days and weeks are shown to one decimal place, while the daily demand echoed back is rounded to a whole number. Demand must be greater than zero and inventory cannot be negative; zero inventory simply gives 0.0 days. The result treats demand as constant and the stock as one pool that can be moved freely between sites, so it says nothing about which individual location runs out first.

Worked example

Three warehouses hold 4,200, 2,650 and 1,800 units, so total inventory is 8,650 units. Their average daily sales are 120, 85 and 60 units, so total demand is 265 units per day. Days of supply: 8,650 / 265 = 32.6 days (32.64 before rounding). In weeks: 32.64 / 7 = 4.7 weeks. At that pace the whole network covers a little over a month of sales.

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Common mistakes

  • Entering one warehouse's stock against the whole company's demand (or the other way round), which makes the cover look far too short or too long.
  • Mixing units: inventory in cases and demand in single items, or demand per week typed as if it were per day.
  • Using last month's total sales instead of the daily average; divide monthly sales by the number of days first.
  • Reading a healthy combined figure as proof that every site is safe; stock in one city does not help a store that has already sold out.
  • Including stock that is on order, damaged or reserved in the on-hand total, which overstates the days left.

Sources

About this calculator

Days of supply (also called days of inventory on hand) tells you how many days your current stock will last before running out, given a rate of demand. For a business with several warehouses or stores, the useful number is often the combined figure — total on-hand inventory across all locations divided by total daily demand across all of them.

Looking at locations individually can be misleading: one site might look dangerously low while another is overstocked, when pooled together the network is fine, or vice versa. Supply chain planners, inventory managers, and retail operations teams track combined days of supply to decide when to trigger a network-wide reorder, spot systemic overstock or shortage risk, and plan transfers between locations before individual sites run out.

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Comments (1)

  • Editorial team

    Run it once for the whole network and again for each site with that site's own stock and demand. The smallest per-site figure shows where stock runs out first, and its gap to the network figure shows how unevenly stock is spread. The default 5000 units at 120 a day is 41.7 days. How do you set daily demand: trailing 30 days or a forecast?

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