How much stock do you actually have left? The math behind the stockout date
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Knowing a product is starting to run low says nothing precise. Knowing there are 6 days of stock left at the current pace does, and it lets you act before the stockout instead of reacting after it. The calculation behind that estimate isn't complicated, it just has to be applied consistently rather than guessed.
The basis: an average consumption rate, not a hunch
The first step is measuring how many units go out per day on average, over a reference period (30 days is a common choice, long enough to smooth out one-off swings, short enough to stay representative of recent activity). This number replaces the subjective impression with something verifiable.
Calculating the number of days left
Once the average daily consumption is known, dividing the stock quantity by that average gives the number of days left before a stockout, at the current pace. A product with 40 units in stock and an average of 5 units going out per day lasts 8 days, not a while longer.
Why a rolling window changes everything
An average consumption calculated once and never updated goes stale the moment activity changes (seasonality, a new customer, a discontinued product). Recalculating over a rolling window, one that moves forward every day, keeps the estimate tied to recent reality instead of a snapshot from months ago.
The limits worth knowing
This calculation assumes fairly regular consumption. A product used only during a seasonal peak or a one-off event will get a skewed estimate during a quiet period, or an overly high one right after a spike. Useful as a daily reference point, not as an infallible forecast for a highly irregular product.
From forecast to order
Knowing the number of days left makes it possible to calculate a suggested reorder quantity: restocking to a target level before the countdown hits zero, instead of ordering an arbitrary amount once the stockout has already happened.
Frequently asked questions
?Over what period should average consumption be calculated?
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30 days is a good compromise for most businesses: long enough to smooth out day-to-day swings, short enough to reflect recent activity rather than an outdated average.
?What about a product with very irregular consumption?
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The calculation stays indicative for that kind of product. It's better to rely on a manual threshold alert, set by hand based on real knowledge of the business, rather than on an average that doesn't reflect occasional use.
?Does the suggested reorder quantity account for supplier lead time?
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The base calculation gives a number of days left at the current pace, without factoring in supplier lead time. It's up to the user to compare that lead time against the days left to know whether there's enough margin before ordering.
See Fluxalyo's consumption forecasting module →