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Inventory Planning Calculator

Inventory planning answers one question: how many units do you need on hand to cover demand for a chosen period, and how many whole cases does that translate into?

Units needed = monthly demand × months of coverage, plus optional safety stock. Cases required = units needed ÷ units per case, rounded up.

Calculator

Plan Your Coverage.

Your assumptions

Units you expect to sell each month.

How long the order should last.

%

Optional buffer for demand spikes and lead times.

Results update instantly. Nothing you enter is saved or sent anywhere.

Results

Base units
60
Safety stock units
6
Units needed
66
Cases required
14
Purchasable units
70

Whole cases only.

Excess units
4
Coverage
2.33 months

Coverage reflects the rounded-up case quantity, not the raw requirement.

Method

How the Plan Is Built.

  1. Step 1Estimate demandStart from actual sales history where you have it, and a conservative estimate where you do not.
  2. Step 2Choose a coverage windowBalance reorder lead time and shelf life against the capital you are willing to tie up.
  3. Step 3Add safety stockCover demand variation and delivery delays with a percentage buffer rather than a guess.
  4. Step 4Round to whole casesCase-packed products round up. Check the excess before committing.
Units needed

(Monthly demand × Months) × (1 + Safety stock %)

Coverage first, buffer second. Keep the buffer explicit so you can tune it later.

Example: 30 × 2 months + 10% = 66 units.

What this tells you

Reading the Results.

Written and reviewed by the InstaMed Wholesale business team. Last reviewed September 2026. This is general business education, not legal, tax or financial advice.

FAQ

Common Questions.

How much inventory should a small retailer carry?

Most small retailers plan one to three months of coverage for a proven product and less for an untested one. Coverage depends on reorder lead time, shelf life and how much working capital you can tie up.

What is safety stock?

Safety stock is extra inventory held to absorb demand spikes and delivery delays. It is usually expressed as a percentage of expected demand over the coverage period.

Why does the result round up to whole cases?

Case-packed products can only be bought in full cases, so the purchasable quantity is always rounded up. The excess units are shown so you can see the overshoot.

What if my demand estimate is wrong?

Model a low, expected and high demand scenario. The gap between them tells you how much risk sits in the purchase decision.

Related resources

Keep Building the Model.

CALCULATORCase Quantity CalculatorConvert the units you actually need into the minimum whole cases you can buy, with the excess units shown clearly.Open resource CALCULATORWholesale Margin CalculatorModel case-based buying: case cost, units per case, case count and retail price become cost per unit, inventory investment, potential gross profit and inventory ROI.Open resource GUIDEHow to Model the Economics of a Product BusinessUnit economics, gross margin, inventory investment and ROI, case quantities, participation, repeat purchase, multi-location scaling, break-even and operating costs.Open resource CHECKLISTProduct Business Launch ChecklistAn interactive, printable checklist covering customer definition, inventory model, product mix, economics, MAP, retail pricing, staff, marketing, launch and measurement.Open resource

Industry context: Supplement & Wellness Retailers, Ecommerce Wellness Businesses, Gyms & Fitness Professionals.

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