Inventory Planner
This page runs the whole inventory decision in one place. Enter your numbers once and the pieces interact the way they do in your storeroom: the order size feeds the reorder point, and the certainty you choose sets the buffer and the dollars attached to it.
Everything happens in your browser, and nothing you type is sent anywhere or saved.
Order size
Each order costs you something fixed, and each unit held costs you something ongoing. This is the quantity where the two costs balance.
Order this many
427 units
42.7 orders a year, about every 9 days
The two costs at that quantity
$2,133 + $2,133
Ordering + carrying, $4,266 a year in all
Why ordering cost and carrying cost come out equal at this number
Safety stock
A buffer sized to how much your demand swings and how long you wait, at the certainty you chose.
Keep as buffer
87 units
z = 2.05 at 98% service
Why doubling your lead time only grows the buffer by about 1.4x
Reorder point
Enough to cover an average wait plus the buffer. When the shelf hits this number, order.
Reorder when you hit
787 units
700 to cover the wait, plus 87 as buffer
Carrying cost
Turns your rate into dollars per year, so the trade-offs above are priced in money instead of units.
Holding one unit for a year
$10
25% of a $40 unit
This policy's stock, priced
$3,004 a year
300 units on hand on an average day
Where the 20-to-30% guess comes from, and how to replace it with your own number
Each piece also runs on its own: the order size calculator and the reorder point calculator.