Enter the values used by inventory days of supply
Estimate how many days your on-hand inventory will last at a chosen daily unit demand rate. Enter the assumptions for the same time period and currency, and check any minimum or maximum values displayed next to the input fields.
Sellable units on hand, Expected units sold per day.
Change one variable so you can see the effect without mixing several assumptions.
The worked example below shows the formula and the independently rendered default-input results.
Calculate inventory days of supply from sample inputs
These are the same starting values loaded into the interactive calculator above. The displayed results below come from the same calculation engine as the live tool.
Step 1 — Record the inputs
Step 2 — Identify the formula
Step 3 — Substitute the values
For this exact worked case, use Sellable units on hand = 600 units; Expected units sold per day = 25 units/day. Replace named formula variables with their input values as shown below. Keep the units consistent; a percent is divided by 100 wherever the model requires a decimal rate.
Step 4 — Read the calculated answer
Rounding follows the calculator display: whole units may be rounded up when an indivisible unit is required, while other values typically show up to two decimal places. The result is conditional on the entered assumptions, not a market quotation.
How to interpret this inventory days of supply result
Use sellable units and demand measured in the same units. Lead time, inbound orders, promotions and variable demand are not automatically included.
Connect the number to a replenishment, capacity, or working-capital decision. Verify whether the data represent actual demand or a forecast.
Scenario comparison
Compare average demand with a peak-demand period and extend the lead time to see where the plan becomes fragile.
Assumptions and limitations
Lead-time variation, supplier constraints and demand spikes can make a simple average misleading.
- Sellable units on hand: Enter a finite numeric value of at least 0. Use a consistent definition across comparison cases.
- Expected units sold per day: Enter a finite numeric value of at least 0.01. Use a consistent definition across comparison cases.
Frequently asked questions
What does this calculator include?
It uses the named inputs above and the formula shown in the worked example. No other fees, revenue streams, or external data are automatically included.
Why could my real result be different?
Lead-time variation, supplier constraints and demand spikes can make a simple average misleading.
How should I compare two results?
Compare average demand with a peak-demand period and extend the lead time to see where the plan becomes fragile. Record the assumption that changed so a higher or lower answer is interpretable.
Inventory Days of Supply calculation method
Use sellable units and demand measured in the same units. Lead time, inbound orders, promotions and variable demand are not automatically included.
What this estimate does—and does not—include
This tool is designed for quick planning and comparison. For tax, accounting, legal, investment, lending, or other regulated decisions, verify the result against the rules and assumptions that apply to your situation.
CalcScoutHQ shows the calculation logic so you can check assumptions, understand the result, and reproduce the math independently when needed.