What the calculation measures
When on-hand plus reliably inbound inventory reaches the reorder point, the next order should arrive before expected demand consumes remaining stock.
How to interpret the result
Increase safety stock when demand or supplier lead time is volatile, not simply because inventory feels low.
Run scenarios instead of one answer
Change the most uncertain input and compare outcomes. A calculator is most useful when it shows sensitivity, not when one estimate is treated as a guarantee.
Limits and assumptions
Seasonality, minimum order quantities and service-level targets can require a more advanced model.