Days of Supply (DOS / DIO)

Days of supply is stock divided by a demand rate: how long what you hold would last at the pace you are consuming it. Weeks of supply and days on hand are the same ratio in different units, and days of inventory outstanding is the same ratio in dollars — the inventory leg of the cash-to-cash cycle.

The demand basis is the whole argument. Trailing days of supply divides by what actually shipped over some past window; forward coverage divides by what the plan says will ship. They agree in a steady-state portfolio and disagree exactly when it matters — on a ramp, into a season, on an item approaching end of life. Trailing coverage on a product about to be discontinued looks comfortable right up to the moment the demand stops.

The second thing to settle before publishing is what happens where demand is zero. Mathematically the answer is infinite; operationally those items are the most interesting inventory in the portfolio. Letting them drop out of the number, or letting them run to infinity inside an average, are both ways of not looking at them.

Also answers to DOS · DOH · Days on Hand · DIO · Weeks of Supply · Forward Coverage

Three switches. The first one has to be labeled on every chart, because trailing and forward coverage answer different questions and look identical.

• Averaging coverage across items — The classic never-average-a-ratio failure. A mean of item-level days of supply is dominated by whichever items happen to have thin demand; pool the stock and pool the demand, then divide.
• Infinite days — Items with no demand either blow up the average or get quietly excluded, and both versions lie. Cap the value, and publish the count of capped items beside the number.
• Trailing and forward switched mid-deck — Two slides, two demand bases, one metric name — and an audience that reasonably assumes they are comparing like with like. Label the basis on the chart itself.
• Window sensitivity — A 30-day trailing window and a 90-day trailing window are different metrics that share a name, and the difference is largest exactly where demand is changing. Print the window.
• Coverage read off the planning grid — Coverage read off a planning grid carries two reading rules. The projected-balance row is a closing balance per bucket — a LAST, never a sum down the time axis. Bucket dates are a vendor rule: Oracle dates supply and demand to a non-daily bucket's last working day, firm, implement and input-data dates exempt, so finer coverage is precision the grid does not carry — an inference from that rule, not the grid: SAP's Advanced MD04 dates elements individually. Name your system's bucketing rule before quoting coverage finer than the bucket.

Stock by storage location on MARD with valuation on MBEW for the value cut. The demand side comes from movement or order history rather than from a stock table, so the window you sum it over is an explicit choice.

F41021 carries the balance and F4111 the movements that give a trailing demand rate. If the demand basis is forward instead, it comes from the forecast file, with the forecast type in the key.

InventSum is on-hand and InventTrans supplies issues for a trailing rate; ForecastSales is the forward basis. Pin the company, and reach site or warehouse through InventDim.

MITBAL and MITLOC carry the stock side per warehouse and location. The time-phased plan supplies forward demand, with the order category deciding which rows are plan rather than firm demand.

Sum the on-hand quantity detail before joining anything to it — the table is finer-grained than the item and organization it is usually treated as. Material transactions give the trailing rate; forecast dates give the forward one.

These carry the stock side and the trailing demand rate. A forward basis has to come from planning extracts landed beside them, so a forward coverage view in Fusion depends on two extract paths staying in step.