Product Inventory Calculator
Calculate reorder points, safety stock, and optimal order quantities for salon product inventory.
About this calculator
This calculator keeps three separate concerns apart: when to reorder, how much to order, and whether current stock might expire before it is used. Reorder Point converts Weekly Usage into a daily rate, then adds together how much gets used during Lead Time plus a Safety Stock Buffer measured in the same daily units, rounded up with Math.ceil (lines 10-13). Current Stock and Cost per Unit never enter that calculation at all -- Current Stock only feeds Needs Reorder Now and Days Until Reorder, comparing itself against the already-computed Reorder Point (lines 15-16), and Cost per Unit only feeds Optimal Order Quantity, Monthly Product Cost, and Annual Product Cost, a completely separate branch of the formula (lines 19-26).
Optimal Order Quantity uses a simplified economic-order-quantity formula built from annual usage, a fixed $25 assumed order cost, and a 25% annual holding-cost rate applied to Cost per Unit (lines 19-23). Expiration Risk compares how many days the current stock would last at the current usage rate against Shelf Life converted to days, and flags risk only when stock would outlast the product's shelf life before it is used up (lines 29-31) -- Shelf Life has no effect on any other output on the page.
Inputs
Results
Reorder Point
9 units
How to Use This Calculator
- Enter each product name, current quantity on hand, and unit cost.
- Set the weekly usage rate and lead time for reordering.
- Review the reorder point and recommended order quantity for each item.
- Use the total inventory value to manage cash tied up in product stock.
- Reorder flagged items before reaching zero to avoid service cancellations.
How the result changes with Weekly Usage
| Weekly Usage | Reorder Point |
|---|---|
| 2.5 | 5 units |
| 3.75 | 7 units |
| 7.5 | 13 units |
| 13 | 23 units |
What each input means
- Weekly Usage
- Average units consumed per week
- Cost per Unit
- Purchase price per unit
- Lead Time
- Days between ordering and receiving
- Safety Stock Buffer
- Extra days of stock to keep as buffer
- Current Stock
- Units currently on hand
- Shelf Life
- Product shelf life after purchase
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersWeekly Usage = 5, Cost per Unit = 12, Lead Time = 7, Safety Stock Buffer = 5 = 6 input(s) provided
- Calculate Reorder PointReorder Point9 = 9
- Calculate Needs Reorder Now0 = 0
- Calculate Days Until ReorderDays Until Reorder15 = 15
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why doesn't Current Stock affect the Reorder Point I should order at?
Reorder Point is built entirely from Weekly Usage, Lead Time, and Safety Stock Buffer (lines 10-13) -- Current Stock is never part of that formula. It is only used afterward, compared against the already-computed Reorder Point to decide Needs Reorder Now and to count down Days Until Reorder (lines 15-16), so it can change whether you need to order today without ever changing the threshold itself.
Why doesn't Cost per Unit change my Reorder Point or Safety Stock?
Reorder Point and Safety Stock are both derived purely from Weekly Usage, Lead Time, and Safety Stock Buffer (lines 10-13) -- Cost per Unit never enters that calculation. It only affects Optimal Order Quantity, Monthly Product Cost, and Annual Product Cost, a separate set of outputs built from annual usage and a 25% holding-cost assumption (lines 19-26).
Which matters more for Reorder Point -- Weekly Usage or Lead Time?
Weekly Usage, by roughly double the effect. Weekly Usage sets the daily usage rate that both the lead-time portion and the safety-stock portion of Reorder Point are built from (line 10), while Lead Time only scales the lead-time portion on its own (line 11), so a 10% change in Weekly Usage moves Reorder Point noticeably more than the same percentage change in Lead Time.
What does Expiration Risk actually check, and why doesn't it show up for most inputs?
Expiration Risk compares how many days your Current Stock would last at your current usage rate against Shelf Life converted to days, and flags risk only if stock would outlast the product before it is used up (lines 29-31). For most realistic salon usage rates, current stock gets used well before a multi-year shelf life expires, so the flag only trips for slow-moving products or unusually short shelf lives.
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