Days of Supply Calculator
See how long inventory will last at your current usage rate, flag low coverage, and compare stock on hand with incoming supply.
Inventory and usage
Paste comma- or semicolon-separated CSV, including the header. Use decimal points without thousands separators, YYYY-MM-DD dates, and one consistent unit per item. Use the shown column names; unrecognized columns are refused. IDs are case-sensitive text: leading zeros are kept. Each paste supports up to 5,000 data rows. Calculations run in your browser; nothing is uploaded.
item, on_hand, plus exactly one of adu or monthly_usage per row; optional open_supply defaults to zero.
Stock coverage
3 items: 2 below threshold, 1 with no usage. Selected coverage includes open supply, as of 2026-11-01.
| Item | ADU | On hand | Open supply | On-hand days | Selected days | Coverage date | Status |
|---|---|---|---|---|---|---|---|
| A | 10 | 120 | 30 | 12 | 15 | 2026-11-16 | Below threshold |
| B | 10 | 60 | 0 | 6 | 6 | 2026-11-07 | Below threshold |
| C | 0 | 40 | 0 | Undefined | Undefined | No usage | No usage |
Selected days of supply by item
Bars share a scale from 0 to 15 days.
- A15 days · Below threshold
- B6 days · Below threshold
- CNo usage · No usage
Formulas and worked example
ADU = monthly usage ÷ 30.44 when daily usage is not supplied. On-hand days = on hand ÷ ADU. With open supply included, days of supply = (on hand + open supply) ÷ ADU. Coverage date = as-of date + floor(days of supply). Flag when selected days are below the chosen threshold. Zero usage has no defined days of supply or coverage date.
On November 1, 2026, item A has 120 units on hand, 30 units of open supply and ADU of 10. On-hand coverage = 120 ÷ 10 = 12 days. Including supply, coverage = (120 + 30) ÷ 10 = 15 days, running out on November 16, 2026. It is below a 20-day threshold. Item B’s monthly usage of 304.4 means ADU = 10; 60 units give 6 days, through November 7. Item C has zero usage and is flagged No usage. All example numbers are locked by calculation tests.
FAQ
How is monthly usage converted?
Average daily usage = monthly usage ÷ 30.44, the same average month length used by the buffer calculator. Supply exactly one of adu or monthly_usage per row. Zero usage is allowed and is flagged separately; blank usage is missing data.
How is the coverage date calculated?
Coverage date = as-of date plus the whole-number part of days of supply, using calendar days. For example, 1.5 days from November 1 runs out during November 2. A zero-usage item has no calculable exhaustion date. Seasonal demand, weekends and future demand changes are not modeled.
Does open supply prevent a stockout?
Only if it arrives in time. Including open supply assumes it is available on the as-of date; this tool does not model receipt dates. Compare the on-hand-only days column before relying on incoming orders. The checkbox controls the selected coverage, coverage date, chart and threshold flags.
Why are no-usage items flagged?
Dividing by zero does not provide a useful coverage estimate. These items show No usage and no coverage date, even when stock is zero. Review whether the item is inactive, new, seasonal or missing demand history.
Is my data uploaded?
No. Calculations and CSV parsing run in your browser, and the numbers and files you enter are never sent to a server, unless you choose to share a link, which carries the single-item inputs in its address. The page has no ads, sign-up or third-party trackers; the site host keeps standard anonymous visit counts.
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