Economic order quantity calculator
The classic Wilson EOQ calculator returns Q* = sqrt(2DS/H), where D is annual demand, S is fixed order cost, and H = i*C is annual holding cost per unit. Output includes Q*, annual holding cost (Q*/2)*H, annual ordering cost (D/Q*)*S, total annual variable cost, and a sensitivity strip showing Q* at carrying-cost percent +/- 3 percentage points[1].
How to read the result
Q* is the order size that balances the two competing annual costs: holding cost (which rises linearly with Q) and ordering cost (which falls hyperbolically with Q). At Q* the two are equal; that is the closed-form algebraic signature of the Wilson model[2].
When the classic Wilson model does not apply
Five assumptions: (1) demand is known and constant; (2) order cost S is fixed per order; (3) holding cost H is constant per unit per year; (4) lead time is zero or known and fixed; (5) no quantity discounts, no shortages allowed. Break any of those and you need a variant: quantity-discount EOQ, backorder allowance, EPQ for in-house production, or a stochastic-demand newsvendor / (s,S) policy.
How the sensitivity strip works
We recompute Q* at carrying-cost percent values 3 points below and 3 points above your chosen i. The result is typically modest, on the order of 6 to 7 percent either way, because Q* depends on the square root of D/H, so the cost function is famously flat near its minimum[3]. That flatness is the practical reason mis-estimated H rarely destroys the answer.
Export the result for a board pack
The sensitivity strip is the column a CFO will ask for. Screenshot it; paste it next to the Q* answer; the carrying-cost percent you used and the resulting Q*, holding, ordering, and total annual cost are the five numbers you need to defend the order quantity. The CSV template walks the same calculation across an entire SKU file.